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Broxbourne Transport Modelling

Technical Note summarising the use of the Broxbourne

Highway Model to support the production of the

Broxbourne Transport Strategy

Broxbourne Borough Council

November 2017

Broxbourne Transport Modelling Technical Note

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Document: Transport Modelling Technical Note

Project: Broxbourne Transport Strategy

Client: Broxbourne Borough Council

Job Number: A100610

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Contents

1. Background .......................................................................................................... 4

1.1 The Commission .......................................................................................................... 4

1.2 The Broxbourne Highway Model ................................................................................... 4

1.3 Traffic Counts ............................................................................................................. 5

1.4 Hertfordshire COMET Model ......................................................................................... 6

1.5 Phases of Modelling ..................................................................................................... 6

2. Phase 1: June 2016 – September 2016 ................................................................... 7

2.1 Overview .................................................................................................................... 7

3. Phase 2: October 2016 – January 2017 ................................................................... 9

3.1 Overview .................................................................................................................... 9

3.2 Reference Case Modelling ............................................................................................ 9

3.3 Initial Scheme Option Modelling ................................................................................. 10

3.4 Additional Scheme Option Modelling ........................................................................... 12

3.5 Cost Analysis............................................................................................................. 14

3.7 Comparisons with the Base Year ................................................................................ 16

3.8 Traffic Growth ........................................................................................................... 17

4. Phase 3: February 2017 – April 2017 ..................................................................... 20

4.1 Overview .................................................................................................................. 20

4.2 Building a Revised Forecast Model .............................................................................. 20

4.3 Scenario Assessments ............................................................................................... 24

4.4 Task 1: Alternative Junction Treatment at A10 / Church Lane ...................................... 25

4.5 Task 2: Cheshunt Lakeside Development Quantum ..................................................... 26

4.6 Task 3: Fishpools Roundabout ................................................................................... 27

4.7 Task 4: Brookfield & Halfhide Lane ............................................................................. 28

4.8 Task 5: Turnford Southern Slip Road .......................................................................... 28



4.9 Task 6: Old A10 ........................................................................................................ 29

4.10 Task 7: Junction improvements (off A10).................................................................... 30

4.11 Task 8: Preferred Scenario ......................................................................................... 31

4.12 Comparisons with the Base Year ................................................................................ 34

4.13 Wider Impacts .......................................................................................................... 36

5. Summary ............................................................................................................. 37


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1. Background

1.1 The Commission

In November 2016, WYG were commissioned by Broxbourne Borough Council (BBC) to 1.1.1

develop a Transport Strategy to support the Broxbourne Local Plan. At the heart of this was the need for a sound and robust evidence base to inform the direction of the Strategy and

the individual schemes required to facilitate growth.

This technical note details the use of the Broxbourne Highways Model to provide part of the 1.1.2

evidence base to support the Strategy.

1.2 The Broxbourne Highway Model

It was agreed with Broxbourne Borough Council (BBC) and Hertfordshire County Council 1.2.1

(HCC) that two existing transport models would form the basis to understanding the future

operation of the transport network across Broxbourne and the surrounding area. The transport models available for use were the Broxbourne Highways Model (Saturn) and the

COMET countywide multi-modal model.

The Broxbourne Highway Model (BHM) was developed by JMP Consultants Ltd on behalf of 1.2.2

Broxbourne Borough Council to assess the highway impacts of a number of different spatial planning scenarios associated with the development of the emerging Broxbourne Local Plan.

This model is a Saturn highways assignment model developed by cordoning and refining the 1.2.3

East London Highway Assignment Model (ELHAM) to provide greater detail in the Broxbourne area. It was updated to a 2013 base year for model validation.

The model represents the AM and PM peak periods of 08:00-09:00 and 17:00-18:00 1.2.4respectively with a ‘pre’ peak model run initially and fed to the main peak model for each

period to ensure that conditions in the model are representative of those on the ground at the start of the peak hour period (rather than starting from an empty network).

Three separate user classes are included in the model namely: Cars (including taxis), Light 1.2.5Goods Vehicles (LGV) and Heavy Goods Vehicles (HGV). Vehicle data was converted from

numbers of vehicles to Passenger Car Units (PCU’s) prior to use in the model in order to more fully represent the impact of larger vehicles on the highway infrastructure.

Initial forecast models were produced by JMP for a forecast future year of 2029. However, 1.2.6

following the initial modelling work, BBC commissioned AECOM to update the future forecasts to 2023 and 2033 to align with the latest Local Plan growth forecast at the time of modelling.

For full details of development of the existing models, please refer to the appropriate 1.2.7

JMP/AECOM reports including:

Broxbourne Transport Study: Model Development and Validation Report, Local Model

Validation Report (LMVR) (Issue 2, May 2014);

Broxbourne Transport Study: Model Development and Validation Report, LMVR Addendum

(Nov 2015); Broxbourne Local Plan Development: Forecasting Report (Nov 2015);

Broxbourne Transport Strategy Phase 2: Existing Conditions and Opportunities (May

2016); and

Broxbourne Transport Strategy Phase 2: Interim Evidence Report (August 2016).


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1.3 Traffic Counts

Central to the development of the model was the collection of data to reflect actual traffic 1.3.1flows on the network. A series of data sources were utilised for this purpose.

Existing TfL Data

JMP had previously undertaken extensive traffic counts on behalf of TfL within the Greater 1.3.2

London area. Several of these counts were located within the study area and were included in the model – notably on the A10 and Great Cambridge Road in the Turnford area, together

with a site on the A10 immediately to the south of M25 J25.

Existing Local Authority Data

Hertfordshire County Council provided traffic data taken from their permanent Automated 1.3.3

Traffic Counts (ATCs) in place across the borough together with additional monitoring data including site measurements for speed, volume and junction turning movements.

Additional Traffic Surveys – Automated Traffic Counts

To supplement the existing data, JMP commissioned a series of further surveys at 19 1.3.4

locations during June 2013. These traffic surveys were utilised in calibrating/validating the Broxbourne model to yield a robust representation of on-site conditions between 13th to 27th

June 2013.

In addition, JMP were also commissioned by Broxbourne Council to assess the impact of a 1.3.5scheme in the Waltham Cross area for which JMP commissioned further traffic counts in

November 2013 that were incorporated into this study.

Additional Traffic Surveys – Manual Counts

A series of Manual Classified Counts (MCCs) were undertaken across the study area at 14 1.3.6

locations, collecting all turning movements at the defined junctions for a 12-hour period,

although detailed analysis was provided for the 3-hour AM and PM peaks (0700-1000 and 1600-1900 respectively). The surveys were performed on a mid-week day (i.e. between

Tuesday and Thursday) during the same time period as the ATCs were being carried out.

Origin Destination (OD) survey

In order to capture the origin and destination points of external to external trips, Automatic 1.3.7

Number Plate Recognition (ANPR) cameras were set up around the study area boundary,

with an additional camera in the middle of the borough to further refine the results. The data from the cameras was then analysed to identify matching pairs of readings to identify

individual trips.

Trafficmaster Data

Finally, in order to determine journey times, data was obtained from the Trafficmaster 1.3.8

system and supplied by Hertfordshire County Council before being analysed by JMP to assist in the validation of the model.

More information on the data collection process is available from Broxbourne Transport 1.3.9Study: Model Development and Validation Report, LMVR Addendum (Nov 2015).


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1.4 Hertfordshire COMET Model

The Hertfordshire COMET Model is a multi-modal model with variable demand model 1.4.1capability. This allows the model to identify the issues and impacts associated with different

growth scenarios and mitigations, whether they are highway based schemes, public transport improvements, or walking, cycling and demand management based interventions.

The model was developed by the County Council to be used as a tool through which to 1.4.2assess transport policies and strategies on a consistent basis across Hertfordshire. As a

strategic model, it provides an important overview of the implications of investment in Broxbourne on the wider transport network to supplement the more refined analysis of the

Broxbourne Highway modelling. The model has a 2014 base year and utilises a 2031 forecast year.

1.5 Phases of Modelling

Due to the size and complexity of running the COMET model, it was determined that the 1.5.1

most feasible course of action would be to test the packages of highways improvements in

the Broxbourne Highways Model (BHM) and then commission a COMET Multi-Modal SATURN Model of the preferred option to verify the impact of the measures at a more strategic county

wide level.

This technical note therefore sets out the packages tested, the methodology employed in 1.5.2using the BHM, the model results and identifies a preferred option to take forward for further

consideration.

Three distinct phases of modelling were undertaken using the BHM to inform the 1.5.3

development of the Transport Strategy:

Phase 1: June 2016 – September 2016

This first phase of modelling was undertaken by consultants AECOM who considered a

number of development scenarios within the model. This is summarised in Chapter 2 of this Technical Note, whilst a separate report detailing the outcomes of this work has also

been published1.

Phase 2: October 2016 – January 2017

Given the deliverability concerns associated with the scenarios AECOM assessed, a

further set of scenarios were identified by WYG. This assessment used the same levels of traffic as the 2016 AECOM assessments in order to allow direct comparison between the

results. This is summarised in Chapter 3.

Phase 3: February 2017 – April 2017

Following the development of the new forecast model in February 2017 as a result of

concerns with its validity, a series of highway network improvement options were considered at several junctions across Broxbourne where congestion issues were

identified, and at locations where new development would necessitate changes to the existing network. These assessments are set out in Chapter 4.

1 Broxbourne Transport Strategy Interim Evidence Report; August 2016, AECOM


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2. Phase 1: June 2016 – September 2016

2.1 Overview

Consultants AECOM undertook the first phase of modelling using the Broxbourne Highway 2.1.1

Model (BHM) in June 2016. They utilised the BHM to assess four scenarios containing various potential packages of mitigation.

These focused upon improvements to the junctions with the A10 and included the 2.1.2

consideration of l grade separated options at the Lieutenant Ellis Way, College Road and

Church Lane interchanges.

At grade solutions and an A10 widening scheme were also considered in terms of their 2.1.3impact on volume of traffic, level of stress and delays on the network. Journey times

between set points within the Borough were assessed as a measure to test relative connectivity.

Ultimately none of the scenarios were deemed both effective and deliverable. Whilst the 2.1.4scenarios which included grade separation highlighted some benefits, their associated costs

would be such that they would be undeliverable under current circumstances.

The results of this assessment are detailed in the Broxbourne Transport Strategy Phase 2: 2.1.5

Interim Evidence Report2.

The future year models available as a basis for further study (for 2023 and 2033 forecast 2.1.6years) therefore consisted of six modelled scenarios. These were:

Reference Case Growth;

Local Plan Growth;

Highway Schemes Option 1 (Scenario 1),

Highway Schemes Option 2 (Scenario 2),

Highway Schemes Option 3 (Scenario 3), and

Highway Schemes Option 4 (Scenario 4).

The Reference Case scenario refers to the level of traffic growth assumed if only background 2.1.7

increases in trips (such as those caused by economic factors/increased car ownership etc) and committed developments go ahead (defined as ‘near certain’ or ‘more than likely’ to

occur in line with Department for Transport guidance).

This assumes no provision of additional development sites for housing or employment over 2.1.8

what already had planning permission at the time of modelling. This also includes the M25 J25 improvement scheme proposed by Highways England.

The Local Plan scenario builds on the Reference Case but includes the new development 2.1.9

areas set out in the emerging Local Plan and any associated planning conditions for

development (such as the ‘hamburger’ junction arrangement proposed for the Park Plaza Roundabout).

2 Broxbourne Transport Strategy Phase 2: Interim Evidence Report; AECOM, August 2016


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The Highways Scheme Options model test highway mitigation packages aimed at supporting 2.1.10

the additional traffic generated by the Local Plan proposals. Further details of the Phase 1 Highways Schemes Options are given in Appendix A.


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3. Phase 2: October 2016 – January 2017

3.1 Overview

The second phase (and all subsequent phases) of modelling to inform the emerging 3.1.1

Broxbourne Transport Strategy were undertaken by WYG.

In discussion with Broxbourne Borough Council, a packages of highways scheme options 3.1.2were developed to be tested in the transport model. These consisted of at-grade and grade-

separated proposals at the following junctions:

A10/ Lieutenant Ellis Way Roundabout;

A10/College Road; and

A10/Church Lane.

The scheme options (see Appendix A for details) were tested using the 2033 model for the 3.1.3AM and PM peak periods. No assessments were made in the 2023 intermediate year.

3.2 Reference Case Modelling

In order to test the scheme options, a reference case model was required against which each 3.2.1

can be compared. Initially, the Local Plan Model as supplied by AECOM was to be used as the reference case for this study. However, on review of the model, a small number of junctions

were identified that needed revision in order to provide a suitable basis against which to test

the options. These were:

A10/Lieutenant Ellis Way Roundabout,

The proposed B198/Park Plaza access junction immediately to the west of the A10/

Lieutenant Ellis Way Roundabout, and The A10/Great Eastern Road/Park Plaza Access junction.

The A10/Lieutenant Ellis Way Roundabout was included in all of the scenarios provided by 3.2.2AECOM as the proposed north-south hamburger signalised junction. As this was one of the

options to be tested, it was determined that the junction should be reverted to the existing

priority roundabout arrangement for the reference case despite it being one of the Masterplan planning conditions for the development of the Park Plaza site.

The B198/Park Plaza access was interrogated in the model. This junction was coded as a 3.2.3

priority junction with egress from the Park Plaza development having priority over the

eastbound B198 traffic movement. As this junction arrangement is unlikely to be achievable on a dual carriageway, this junction was subsequently remodelled as a 3-stage signalised

junction.

The A10/Great Eastern Road/Park Plaza Access junction is an all movement 4 arm signalised 3.2.4

junction. In the models supplied, 2 lanes were coded as available for the A10 north-south movements. However, on inspection of aerial mapping, the existing 3 arm junction has 3

lanes available for both of the ahead movements on the northern and southern A10 approaches.

It is unlikely that a reduction in lanes for the main A10 movements would be feasible in the 3.2.5future forecast year given the current and predicted levels of traffic. Therefore, the model


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was revised to allow the ahead and left movement in lane 1 on both approaches (coded as

left only previously). The revised models were run for the 2033 AM and PM peak periods.

Initial results from the revised reference case indicated a significant amount of delay on the 3.2.6

east and west approaches to the A10/Lieutenant Ellis Way Roundabout. In particular, the delay to the B198 approach caused vehicles to switch to alternative routes with a reduction in

eastbound flow to only approximately 30 Passenger Car Units (PCU’s) and 680 PCU’s westbound on the A121 in the AM peak.

Similarly, the PM peak flows were approximately 40 and 490 PCU’s eastbound and westbound 3.2.7respectively. This is due to the significant increase in A10 north-south traffic that effectively

blocks the east and west approaches to the roundabout. Appendix B gives demand flows on links in PCU’s.

Other areas of significant congestion include the approaches to the College Road and Church 3.2.8Lane junctions with the A10, Theobalds Lane, links parallel to the A10 such as Crossbrook

Street and Monarch’s Way and the Brookfield Lane West/Flamstead End Road junction. Appendix B shows nodes and links with volume over capacity ratios in excess of 85% for

the AM and PM peak models.

3.3 Initial Scheme Option Modelling

Two scheme options were derived for the A10/Church Lane and A10/College Road junctions. 3.3.1These consisted of grade separated/restricted access movements at each junction and at-

grade improvement options to the two existing signalised junctions. The grade separated

options are denoted as Scenario 5 and the at-grade options as Scenario 6. Details of the junction arrangements for both scenarios are given in Table 2 of Appendix A.

For both Scenarios 5 and 6, a series of options were included for the A10/Lieutenant Ellis 3.3.2

Way Roundabout. These were denoted as a suffix to the scenario number as follows:

Blank = priority roundabout as per the revised Reference Case;

a = Grade separated north-south A10 movements;

b = Hamburger style signalised junction with N/S priority;

c = Hamburger style signalised junction with E/W priority; and

d = Signalised junction with localised entry/circulating widening to accommodate

additional lanes.

Each of the resultant 10 scenarios were assigned in the model for each peak period. 3.3.3

Data was collected for the overall network summary statistics, north-south journey times on 3.3.4

the A10 and four east-west journey time routes. The latter of these used the network

modelled shortest path between an origin and destination as the modelled options restricted some traffic movements within the model. As such, some routes assessed were longer than

those generated for the same origin to destination between different scenarios. Results from the models are given in Appendix C.

As can be seen from the network summary statistic tables in Appendix C, the north-south 3.3.5Hamburger out performs the other options for the A10/Lieutenant Ellis Way Roundabout for

both Scenario 5 and 6 in both peak periods.

The Hamburger arrangement provides better overall network statistics than the grade 3.3.6

separated option at the A10/Lieutenant Ellis Way Roundabout. This is due to the introduction


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of traffic signals on the east and west bound approaches as part of the scheme. The

signalisation of these approaches reduces the average delay east and westbound. This has the knock-on effect of allowing more traffic to use these routes instead of the High

Street/Crossbrook Street corridor for example, allowing other traffic to exit zones in this area

more easily.

Furthermore, the conflict point where the roundabout exit link northbound re-joins the A10 3.3.7

carriageway is controlled, enabling the southbound traffic to have a clear exit to the south (due to the increase in southbound lanes) whereas, for the grade separated option, the

traffic needs to merge and is delayed due to the high north-south flow.

When comparing Scenarios 5 and 6, Scenario 6 is generally seen as more beneficial across 3.3.8the network statistics than Scenario 5. This could be considered counter intuitive as the

Scenario 5 options allow for grade separated movements.

However, when comparing the vehicle movements, it can be seen that, in Scenario 5, 3.3.9

vehicles accessing Broxbourne from the A10 at the College Road and Church Lane junctions with the A10, have to re-route due to the restrictions on turning movements that these

options put in place. This re-routing has the effect of increasing total travel times and

distances.

In order to easily rank the journey times, the average time across the outbound and return 3.3.10direction across both peaks was taken for each modelled journey time route. Although this is

an artificial way to combine data, it allows assessment across each peak to be simplified.

Routes by time period and by direction were still scrutinised to ensure no anomalous routes prejudiced the results.

The routes assessed comprised: 3.3.11

A10 between M25 J25 and A1170 (Dinant Link Road, Hoddesdon) – north/south

Between Brookfield and Cheshunt Station – east/west

Between Park Plaza and Waltham Cross Station – east/west

Between Goffs Oak and Cheshunt Station – east/west

For the north-south routes, Scenarios 5a and 5b came out as the best performing. This was 3.3.12

as expected as these routes cater specifically to the north-south movements. It should be noted that the difference between 5a and 5b was relatively small despite 5a including the

more costly grade separation at the A10/Lieutenant Ellis Way Roundabout.

For the east-west routes, some routes were better with different options than others e.g. for 3.3.13

the Brookfield to Cheshunt route, Scenario 6a was quickest outbound in the AM peak whereas Scenario 6b was better for the reverse direction in the same peak. By using the

summary indicator for the four routes, Scenarios 5b and 6b were seen to perform best overall.

It should be noted that for the Park Plaza to Waltham Cross Station route, journey times 3.3.14were seen to be least in the AECOM Local Plan scenario. This is likely due to the access

arrangements onto the B198, as discussed previously, giving undue priority to the Park Plaza access.

Volume over capacity plots for links and junctions are provided in Appendix D, together with 3.3.15plots of demand flow on links for each Scenario and the difference in link demand flows

between each Scenario and the Reference Case model.


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Please note, that for difference plots, no flow differences can be shown where links/node 3.3.16

numbers change due to changes in infrastructure modelling e.g. on the proposed grade separated through link at the A10/Lieutenant Way junction compared to the Reference Case.

Based on the above comparisons, Scenario 6b was seen as the best overall but it did not 3.3.17perform as well as Scenario 5b for the north-south journey time routes.

3.4 Additional Scheme Option Modelling

Based on the results detailed in Appendix C, tests were carried out on the College Road and 3.4.1Church Lane junction proposals in order to establish whether providing one at-grade and one

grade separated/restricted access would capitalise on the benefits of both Scenarios 5b and 6b. Therefore, two further model runs were carried out with the A10/Lieutenant Ellis Way

Roundabout fixed as a north-south Hamburger Junction.

A new Scenario 7b provided additional lanes to increase capacity at-grade at the Church Lane 3.4.2

junction. Right turns would be banned at this junction. At College Road east-west movements would be restricted to all but buses with bus gates in place as appropriate.

Likewise, a new Scenario 8b provided a grade separated junction at Church Lane with no 3.4.3interaction with the A10, with the former at grade and the latter in an underpass. The

scenario provided additional lanes to increase the capacity at-grade at College Road junction but restricted right turn manoeuvres.

The relevant tables from Appendix C have been appended with the results from the 7b and 3.4.4

8b Scenarios and are given in Appendix E. It can be seen from the network summary

statistics that:

Scenario 8b performs better or very close to the next best scenario (6b) in the AM peak.

In the PM peak, the results are similar with Scenario 8b performing better than or close to the next best scenario (5b).

For north-south journey times, Scenario 8b improves on the results of Scenario 6b with

results approaching those of the best scenario (5a/5b).

For the east-west journey times, Scenario 8b performs best over each of the four routes

when averaged across the peaks/directions.

Therefore, based upon balancing north-south and east-west capacity and connectivity 3.4.5requirements, Scenario 8b was seen as the preferred option in terms of network

performance.

Volume over capacity plots for links and junctions, demand flow plots and difference plots 3.4.6

compared to the Reference Case Scenario are provided in Appendix F. These indicate that a number of junctions were still likely to suffer from congested conditions even with the

implementation of the Scenario 8b Highways proposals. These junctions include:


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Winston Churchill Way/High Street;

Monarch’s Way/A121 Eleanor Cross Road;

High Street/Church Lane;

Flamstead End Road/Church Lane;

Flamstead End Road/Brookfield Lane West;

B156 Cuffley Hill/Newgatestreet Road; and

B156/High Road Turnford/Cheshunt Wash.


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3.5 Cost Analysis

Based upon the scenarios assessed, cost ranges per scenario have been calculated. These 3.5.1indicative cost assumptions are broad brush estimates and should be used for information

purposes only. They do not include any detailed costs assessments of the options or of the land take required and its availability. They are based on 2017 cost estimates and do not

include for growth in costs over time such as inflation or increases in building costs3.

Table 1 sets out the cost per scenario assumed and ranks these by relative costs. Based on 3.5.2

the table, it was considered that Scenarios 5a and 6a did not provide good value for money.

Table 1: Indicative Scenario Costs

Scenario Package Indicative Cost (£m)

Likely Cost (relative)

Scenario 6 At grade capacity improvements at Church Lane and College Road (Note: No mitigation proposed at Park Plaza junction in this scenario).

6.0 £

Scenario 7b At grade capacity improvements at Church Lane, access restrictions at College Road, with N/S hamburger at Park Plaza

11.5 £

Scenario 6b At grade capacity improvements at Church Lane and College Road, and N/S hamburger at Park Plaza

13.5 £

Scenario 6c At grade capacity improvements at Church Lane and College Road, E/W hamburger at Park Plaza

13.5 £

Scenario 6d At grade capacity improvements at Church Lane and College Road, with signalisation and widening at Park Plaza

13.5 £

Scenario 5 Underpass at Church Lane and bus gate at College Road (Note: No mitigation proposed at Park Plaza junction in this scenario).

30.1 ££

Scenario 5b Underpass at Church Lane and bus gate at College Road, with N/S hamburger at Park Plaza

37.6 ££

Scenario 5c Underpass at Church Lane and bus gate at College Road, with E/W hamburger at Park Plaza

37.6 ££

Scenario 5d Underpass at Church Lane and bus gate at College Road, with signalisation and widening at Park Plaza

37.6 ££

Scenario 8b Underpass at Church Lane with at grade capacity improvements at College Road, and N/S hamburger at Park Plaza

39.6 ££

Scenario 6a At grade capacity improvements at Church Lane and College Road, and GSJ at Park Plaza

56.0 £££

Scenario 5a Underpass at Church Lane, bus gate at College Road and GSJ at Park Plaza

80.1 £££

Likely Cost (relative) £m

<20 20-40 40+

£ ££ £££

Low Medium High

3 Scheme costings were undertaken by AECOM and are detailed in the A10 Corridor Potential

Transport Interventions Design Investigation Report; AECOM, January 2017

(https://www.broxbourne.gov.uk/sites/default/files/Documents/Planning/pp_A10%20Outline%20Design%20Draft%20Report%2002.11.17.pdf)

https://www.broxbourne.gov.uk/sites/default/files/Documents/Planning/pp_A10%20Outline%20Design%20Draft%20Report%2002.11.17.pdf

https://www.broxbourne.gov.uk/sites/default/files/Documents/Planning/pp_A10%20Outline%20Design%20Draft%20Report%2002.11.17.pdf


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3.6 Scenario Summary

A summary of the scenario results is provided in Table 2 below. 3.6.1

Table 2: Scenario Results Summary

Scenario Package

North-South (A10)

Journey Times

East-West

Journey Times

Indicative Cost

Scenario 5 Underpass at Church Lane and bus gate at College Road

✓ ✓ ££

Scenario 5a Underpass at Church Lane and bus gate at

College Road, with GSJ at Park Plaza ✓ ✓ ✓ ✓ £££

Scenario 5b Underpass at Church Lane and bus gate at College Road, with N/S hamburger at Park Plaza

✓ ✓ ✓ ✓ ✓ ✓ ££

Scenario 5c Underpass at Church Lane and bus gate at College Road, with E/W hamburger at Park Plaza

✗ ✗ ✓ ✓ ££

Scenario 5d Underpass at Church Lane and bus gate at College Road, with signalisation and widening at Park Plaza

✗ ✗ ✓ ✓ ££

Scenario 6 At grade capacity improvements at Church Lane and College Road

– ✓ £

Scenario 6a At grade capacity improvements at Church Lane and College Road, with GSJ at Park Plaza

✓ ✓ ✓ ✓ £££

Scenario 6b At grade capacity improvements at Church Lane and College Road, with N/S hamburger

at Park Plaza ✓ ✓ ✓ ✓ ✓ ✓ £

Scenario 6c At grade capacity improvements at Church Lane and College Road, with E/W hamburger at Park Plaza

✗ ✗ ✓ ✓ £

Scenario 6d At grade capacity improvements at Church Lane and College Road, with signalisation and widening at Park Plaza

✗ ✗ ✓ ✓ £

Scenario 7b At grade capacity improvements at Church Lane, access restrictions at College Road, with N/S hamburger at Park Plaza

✓ ✓ ✓ ✓ ✓ £

Scenario 8b Underpass at Church Lane with at grade capacity improvements at College Road, and N/S hamburger at Park Plaza

✓ ✓ ✓ ✓ ✓ ✓ ££

Scale of Impact (relative)

✓ ✓ ✓ ✓ ✓ ✓ – ✗ ✗ ✗ ✗ ✗ ✗

Largely Beneficial

Moderately Beneficial

Slightly Beneficial

Little Impact Slightly

Negative Moderately Negative

Largely Negative

As can be seen from Table 2, Scenarios 5b, 6b and 8b all offer good benefits in terms of 3.6.2journey time improvements for both the north-south and east-west routes compared to the

reference case scenario.

Of these three scenarios, Scenario 6b could be considered the most cost effective but 3.6.3Scenario 8b offers better results for both east-west and north–south journey times. It also


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more effectively reduces the impact of the A10 in terms of severance for pedestrians and

cyclists although this is something which cannot be quantified within the Broxbourne Model.

The inclusion of at least one grade separated junction is also considered to offer additional 3.6.4

benefits in terms of safe guarding east-west connectivity in Broxbourne particularly if A10 through traffic increases at or above that predicted in the model. As such, it was our

conclusion that Scenario 8b should be taken forward for testing in the COMET model.

3.7 Comparisons with the Base Year

Following the identification of Scenario 8b as the most effective package of measures, and 6b 3.7.1as a more cost effective solution, their performance was assessed against the base year

model.

The tested scenarios returned average north-south journey times comparable with the 2013 3.7.2

base model, despite the increased flows from the twenty years of growth. It highlighted that Scenario 6b is slightly slower, but Scenario 8b is slightly faster.

2013 = Base average travel time is 587 seconds (9:47)

2033 = Sc6b average travel time is 616 seconds (10:16) – 5% / 29 seconds longer

2033 = Sc8b average travel time is 548 seconds (9:08) – 7% / 39 seconds faster.

The east-west average journey times do demonstrate some delay however, as highlighted in 3.7.3

Table 3.

Table 3: East-West Journey Time Summary

Trip Measure 2013 2033 Sc6b 2033 Sc8b

Brookfield to

Cheshunt Station

Secs 343sec 608sec 525 secs

Mins:Secs 5min 43sec 10min 7sec 8min 45sec

Change n/a 1.8x slower 1.5x slower

Goff’s Oak to

Cheshunt

Station

Secs 622sec 819sec 655sec



Park Plaza to Waltham Cross

Station




Park Plaza to Cheshunt

Station




Despite this performance, it should be noted that both scenarios (Sc6b and Sc8b) perform 3.7.4significantly better than a no-mitigation scenario.


17

3.8 Traffic Growth

Following the assessment of these scenarios, an analysis of the traffic growth factored into 3.8.1the modelling was undertaken to address concerns that it had previously been over-

estimated. WYG were provided with AM and PM peak period models for the 2013 Base Year and 2023 and 2033 future year scenarios.

The traffic growth used in the models can be split into three subsets. These are: 3.8.2

Background Growth: This is traffic growth associated with general trends e.g. economic

factors such as car ownership; Reference Case Trips: These are the additional trips associated with committed

developments that would travel through the area. This includes developments in

Broxbourne but also trips generated from developments in other areas such as the

neighbouring districts that would pass through the study area; and Local Plan growth: These are the trips generated by the Local Plan assumptions to be

tested in the model.

The 2033 models are split into Reference Case (RC) and Local Plan (LP) models. The RC 3.8.3

model includes all growth between 2013 and 2033 excluding the Local Plan proposals (i.e. 1 and 2 above). The LP models then add the LP predicted growth (3).

By comparing the Base year and RC forecast year models, it was seen that traffic growth in 3.8.4the area has been modelled to be approximately 29% and 31% between 2013 and 2033 in

the AM and PM peaks respectively. This level of growth was above what was expected by BBC particularly as it does not include the Broxbourne Local Plan proposals.

A review was therefore carried out of the original JMP forecasting reports and additional 3.8.5information was requested from AECOM regarding the methodology employed in future year

forecasting in order to establish whether the percentages given above are appropriate for the future year forecast modelling. Details of the methodology employed are given in the

following sections.

3.9 Growth Methodology

In discussion with AECOM, it was established that the future year growth produced by JMP 3.9.1was not used in the further modelling and as such, only the AECOM methodology was studied

further. The methodology employed was provided by AECOM as follows:

Background Growth

Background Growth (growth not a result of changes in housing stock or employment) was 3.9.2calculated using two separate data sources:

The National Trip End Model version 6.2 (NTEM v6.2) datasets with information extracted

from these using TEMPRO 6.2 (both of which were current Department for Transport

(DfT) guidance at the time of undertaking the work), and The National Transport Model (NTM) Road Traffic Forecasts 2015 (RTF15) for which data

were extracted from Scenario 1 which represents the DfT’s most ‘central’ growth

scenario. Car background growth draws on both the NTEM v6.2 data and the NTM RTF15

data; LGV and HGV growth use just the RTF15 data.


18

LGV and HGV data

NTM RTF15 provides information on vehicle growth at five-yearly intervals from 2010 through 3.9.3

2040. These data are provided by road type and by Government Office Region (GOR). Data for the East of England GOR were used, as this is the area within which the Borough of

Broxbourne is located.

To calculate actual values for 2013 (the model Base Year), 2023 and 2033 (the modelled 3.9.4

forecast years) linear interpolation was undertaken for the years either side (e.g. 2013 assumed a linear interpolation between 2010 and 2015, 2023 a linear interpolation between

2020 and 2025).

Once these data had been calculated, it was then possible to calculate the % growth from 3.9.5

2013 to the two forecast years: LGV growth was based on the growth in LGV miles across all road types in the East of England; HGV growth was based on the growth in ‘Rigid’ and

‘Articulated’ miles across all road types in the East of England.

Car data

Calculation of background growth followed the methodology previously set out in AECOM’s 3.9.6

Briefing Note dated 19th May 2016. Note that this isn’t the total NTEM V6.2 growth between

the Base and forecast year (e.g. 2013 to 2033) but solely that which isn’t due to increases in housing or employment supply, but which would be expected occur solely as the result of

changes in economic factors.

This method is aligned with other highway-only models in use in Hertfordshire, including 3.9.7SHUM and WHaSH.

The background growth was calculated by using the ‘Alternative Assumptions’ method within 3.9.8TEMPRO 6.2, setting housing and employment supply in the two future years equal to that in

2013. All internal-based movements (I-I, I-E, E-I) used ‘Alternative Assumptions’ data extracted for the Borough of Broxbourne; external-external (E-E) movements used a

combination of data from NTEM v6.2 for Hertfordshire (the parent county), the East of

England (parent region) and NTM RTF15 data.

Internal-based movements

Internal-Internal (i.e. trips (zones) wholly within Broxbourne) movements used an average of 3.9.9

the origin and destination growth factors for ‘Car Driver’ trips, extracted for AM and PM peak periods separately.

Internal-External (i.e. trips from Broxbourne to outside the district) movements used the 3.9.10

origin growth factors for ‘Car Driver’ trips, extracted for AM and PM peak periods separately.

External-Internal (i.e. trips from outside the district to Broxbourne) movements used the 3.9.11

destination growth factors for ‘Car Driver’ trips, extracted for AM and PM peak periods separately.

Note that all of the above factors were adjusted for changes in income and fuel, following the 3.9.12methodology set out in WebTAG unit M4 §7.4.13 using the data from WebTAG Databook

Table M4.2.1 (Autumn 2015 release v1.4, December 2015).


19

External-External movements

As there is little coverage outside of the Borough of Broxbourne in the traffic model, external 3.9.13

trips were ‘growthed’ using a combination of NTEM and NTM (WebTAG Unit M4 §9). In this instance, NTEM v6.2 ‘Car Driver’ data for Hertfordshire (AM and PM peak period data

extracted) were combined with the average day ‘Car Driver’ trip-end growth for the East of

England GOR and the NTM RTF15 growth on rural trunk & principal dual carriageway roads in the East of England.

Reference Case car trips

With the background growth calculated (as above), the remainder of the Reference Case trip 3.9.14matrices comprises trips generated by committed developments. This development would

occur regardless of Local Plan implementation or not. The list of committed developments was provided by Broxbourne and includes committed residential and employment

development.

All committed development was expected to be complete by 2033; phasing information 3.9.15

supplied by Broxbourne showed that around 90% of committed developments were due to be complete by 2023, so heavily skewed to earlier years.

These developments were converted to trips through the application of trip rates generated 3.9.16

from TRICS. These used trip rates from JMP work where appropriate with some additional

categorisation undertaken to further develop and distinguish between development types.

The above methodology appears sound. However, based on the methodology given above, 3.9.17matrix analysis was carried out separately by trip type for Internal and External Trips.

Table 4 gives the percentage growth for the Internal and External sectors. 3.9.18

Table 4: Matrix Growth: 2013 Base to 2033 Reference Case by Sector

Movement AM PM

Internal to Internal 35% 37%

Internal to External 25% 36%

External to Internal 35% 32%

External to External 27% 28%

Were the methodology described above effective, the percentages for Internal trips, 3.9.19particularly internal to internal, would be expected to be low as only committed

developments should be included. In fact, the AM peak period shows approximately 7,000 additional trips with one or more trip ends in the internal sector.

To put this into context, an approximate trip rate (two-way) per dwelling in the AM peak can 3.9.20be assumed as 0.6 trips within the hour. Therefore, to generate the additional 7,000 trips,

would require approximately an additional 11,650 dwellings built between 2013 and 2033 were the trips generated by dwellings alone. As the Reference Case should not include any

local plan growth, this value seems well above what would be expected in the area.

Based on the above assessment, it was considered likely that the level of growth in the 3.9.21

model was too high. In order to confirm this assumption, the Uncertainty Log used in derivation of the matrices was requested from AECOM. Analysis of this Uncertainty Log would


20

then contribute to determining whether any changes to the matrices would be required for

further modelling.

4. Phase 3: February 2017 – April 2017

4.1 Overview

There were two key elements to the third and final phase of modelling work undertaken 4.1.1using the Broxbourne Highway Model (BHM):

An update to the Forecast Model; and

Revised scenario assessment

4.2 Building a Revised Forecast Model

The Broxbourne Highway Model covers the borough only, with the area of the borough 4.2.1

divided into 139 zones, called the ‘Internal’ zones. This number includes 23 zones in the model that are there solely to represent new developments. Origins and destinations outside

the borough are represented by 53 zones, called ‘External’ zones.

TEMPRO

TEMPRO, the Trip End Model Presentation Program, is designed to allow detailed analysis of 4.2.2

pre-processed trip-end, journey mileage, car ownership and population/workforce planning

data from the National Trip End Model (NTEM).

TEMPRO is also the industry standard tool for estimating traffic growth, which is required 4.2.3when assessing the traffic impact of a development on the local highway network.

Previous modelling undertaken by AECOM used the TEMPRO version available at the time, 4.2.4version 6.2. WYG updated the forecasting to use the latest TEMPRO version, which is 7.2. It

is worth noting that TEMPRO 7.2 incorporates a recently observed national reduction in trip making and so produces lower forecasts in general than version 6.2, especially from a 2013

base line.

Following the previous methodology adopted by AECOM, WYG applied the ‘alternative 4.2.5

assumptions’ method in TEMPRO to remove growth associated with future developments. This residual ‘background’ growth represents demographic changes that would occur even in

the absence of new development.

TEMPRO gives growth factors for origin and destination trip ends separately. The background 4.2.6

TEMPRO growth was applied in the following way:

Internal-Internal trips (i.e. those starting and ending in Broxbourne) used an average of

the origin and destination growth factors for Broxbourne; Internal-External trips (i.e. those starting in Broxbourne but ending elsewhere) used the

origin growth factor for Broxbourne;

External-Internal trips (i.e. those ending in Broxbourne but starting elsewhere) used the

destination growth factor for Broxbourne;


21

External-External trips (i.e. those passing through Broxbourne but starting and ending

outside the Borough) used the latest National Transport Model (NTM) growth from Road

Traffic Forecasts 2015 (RTF15), with a local correction using TEMPRO.

Trip rates

WYG reviewed the trip rates used in the previous forecasting work. This used TRICS-based 4.2.7trip rates and included reductions for mixed-use sites. WYG also undertook a TRICS

assessment of all the developments from first principals. A comparison of the two assessments is given below in Table 5.

Table 5: Comparison of Trip Rates

Land Use Unit AM In AM Out

AM Two-

way PM In PM Out

PM Two-

way

B1 Office (previous) 100sq.m 1.128 0.014 1.142 0.043 1.056 1.099

B1 Office (WYG) 100sq.m 1.320 0.097 1.417 0.054 1.110 1.164

Houses (previous) per unit 0.161 0.448 0.609 0.396 0.204 0.600

Houses (WYG) per unit 0.140 0.400 0.540 0.369 0.193 0.562

Flats (previous) per unit 0.023 0.255 0.278 0.255 0.104 0.359

Flats (WYG) per unit 0.069 0.217 0.286 0.189 0.084 0.273

Retail (previous) 100sq.m 2.724 1.714 4.438 4.329 5.313 9.642

Retail (WYG) 100sq.m 2.508 2.187 4.695 4.806 5.121 9.927

Primary School (previous) pupil 0.381 0.281 0.662 0.027 0.036 0.063

Primary School (WYG) pupil 0.239 0.162 0.401 0.036 0.039 0.075

Secondary School (previous) pupil 0.086 0.040 0.126 0.005 0.019 0.024

Secondary School (WYG) pupil 0.099 0.051 0.150 0.004 0.016 0.020

The WYG assessment differs slightly from the previous rates. In some cases WYG have 4.2.8

produced lower rates whilst in other cases they are higher. As the previous rates had previously been agreed and there was no significant difference between the rates overall,

WYG used the previously agreed rates in subsequent modelling.

Inter-development trips

The previous methodology did not have any trips going between the new developments. In 4.2.9effect, all trip ends that started or ended at a new development were being counted as a new

trip, whereas in reality some trips ends will be combined into a single new trip, for instance

between new residential and new employment developments.

WYG thus used a methodology (using development size and matrix weightings) that allowed 4.2.10inter-development trips to be made, thus avoiding this form of double-counting. The outturn

percentages of inter-development trips in the matrix are:

AM

Cars: 14%;

LGV: 12%;

OGV: 1%;

PM Cars: 16%;

LGV: 12%;

OGV: 1%;


22

Income and fuel cost adjustment factors

The previous modelling multiplied the trip matrix by income and fuel cost adjustment factors. 4.2.11

For the time period 2013-2033 this represented an increase from the reference case trip

matrix of 15%. WYG did not believe this was applicable to the Broxbourne model for the following reasons:

The congested nature of the highway system and model;

The small size of the model; and

Variable demand models (to which the factors do not apply) often reduce the trips.

These reasons are explained in the following sections. 4.2.12

The congested nature of the model

WebTAG guidance (Unit M4, section 7.4) suggests the use of income and fuel cost 4.2.13adjustment factors for fixed-trip highway-only models (of which the Broxbourne model is an

example). There are however, a number of assumptions in the guidance that do not apply

here.

WebTAG is geared towards developing models for highway scheme appraisal and as such has 4.2.14strict guidelines as to when a model should have full variable-demand modelling. In

particular, fixed-trip models are only expected to be used if there is little congestion.

The Broxbourne model is congested. Therefore, as a fixed-trip model it unlikely to be suitable 4.2.15

for major scheme appraisal but it is fit for purpose for the assessment of Local Plan growth and finding a preferred package of highway mitigation (as we are doing here).

The presence of congestion in the peak hours indicates that there is little room for 4.2.16

unrestrained traffic growth as implied by the use of income and fuel cost adjustment factors.

The small size of the model

Broxbourne is a relatively small district geographically, with a high proportion of car trips 4.2.17starting or ending outside the district. The forecasting assumptions underlying the income

and fuel cost adjustment factors in WebTAG are based on the change to car-kilometres with respect to changes in income or fuel cost.

As noted above, national trip rates are reducing so the increase must be largely due to 4.2.18increases in car journey length. Any trip length increase for trips starting or ending in the

Borough, but with the other trip end elsewhere, will not have any effect on traffic flows within the model. The application of income and fuel adjustment factors increases car trips

not average trip length so is a poor proxy for its stated purpose in our case.

Note that External-External trips (i.e. those passing through Broxbourne but starting and 4.2.19

ending outside the Borough) will be ‘growthed’ by forecasts from the National Transport Model, which is a variable demand model.

Variable demand models hardly change TEMPRO forecasts

In modern congested peak hour networks a variable demand model will hardly increase (and 4.2.20

sometimes reduce) the number of trips in a future reference case model run. This is due to


23

the demand-feedback mechanisms available to reduce demand as a response to high levels

of congestion in the future.

A fixed-trip model such as the Broxbourne Saturn model is unable to alter the reference case 4.2.21

trips as a result of increasing future congestion. In this regard, using the reference case forecasts (as WYG are doing) could even be an over-estimate of trips. Applying income and

fuel cost adjustment factors (an uplift of 15%) to already overly congested networks is not appropriate.

Table 6 shows the action of the variable demand module of two variable demand models. 4.2.22The table gives the matrix totals of the demand segments subject to the variable demand

process. The matrix totals are from 2031 forecast models. The A453 Widening Scheme model used an OD-based incremental variable demand model acting directly on the peak models.

The Hertfordshire COMET model applies the variable demand model at the daily trip level

rather than on the peak periods.

In the table, ‘Reference case’ refers to the forecast trips using TEMPRO growth, whilst ‘Post 4.2.23VDM’ refers to the forecast trips after the variable demand modelling component has been

run. Table 6: Example Variable Demand Model Changes to Reference Demand

VDM model Period Reference case Post VDM % difference

A453 Widening Scheme AM 120,121 120,761 0.53%

A453 Widening Scheme PM 125,013 124,839 -0.14%

Hertfordshire COMET* 24hr 3,091,423 3,102,431 0.36%

*Ref: Hertfordshire COMET: Local Plan Do Minimum Forecasting Report, Dec 2016

It can be seen from the above table that the variable demand process in both models has 4.2.24

produced only slight changes to the trip totals, even reducing the totals in the more

congested PM peak of the A453 model.

Summary

The WYG methodology for re-forecasting the Broxbourne Highway Saturn Model would use 4.2.25

the latest version of TEMPRO (v7.2) and previously agreed trip rates. Trips between the new

developments would be represented for the first time, removing a form of double-counting. Income and fuel cost adjustment factors would not be applied for this model.

Subsequently, this approach generated significantly lower forecast trips than the previous 4.2.26

modelling. With the application of the methodology, the Broxbourne Highway Saturn Model provides a robust and fit-for-purpose model to assess highway infrastructure options to

inform the Broxbourne Transport Strategy.

Table 7: Forecast Growth between 2013 and 2033

Period Previous

modelling WYG

AM 29 % 17 %

PM 31 % 17 %


24

4.3 Scenario Assessments

Following the development of the revised Forecast Model, a series of highway network 4.3.1

improvement options were considered at several junctions across Broxbourne where congestion issues were identified, and at locations where new development would

necessitate changes to the existing network, specifically at:

Turnford Interchange, Turnford

Marriott Roundabout, Turnford

Halfhide Lane, Turnford

Cheshunt Lakeside development capacity, Cheshunt

Church Lane / High Street junction, Cheshunt

Church Lane / Flamstead End Road junction, Cheshunt

Introduction of speed reduction measures on the previous alignment of the A10

Fishpools Roundabout, Waltham Cross

Newgatestreet Road / Goffs Lane junction, Goffs Oak

The assessment of these schemes was undertaken within the previously identified Scenario 4.3.28b to provide details of a final preferred scenario to assess within the Hertfordshire COMET

model.

Reference Case Network

In order to assess the highway infrastructure options, a revised Reference Case network was 4.3.3created. This network includes the committed development allocations and changes to

background growth for the 2033 modelled year as described in Section 4.2 and the Local Plan development growth but did not include any highway infrastructure improvements.

As such, it provided a worst case scenario where the Local Plan identified development traffic 4.3.4growth is included on the existing highway network and can be used to provide a base line

against which the highways infrastructure improvements can be compared.

Highway network changes which are included in the Reference Case compared to the Base 4.3.5model are:

Access points to allow Local Plan development sites to be loaded into the model including

the A10/Dinant Link Road ‘dumbell’ roundabout and Brookfield Turnford Link initial development infrastructure;

More detailed representation of the Fishpools Roundabout;

Speed restriction on BlindMan’s Lane to represent the current traffic conditions;

More detailed representation of the High Road Turnford/Thomas Rochford Way

Roundabout; Capacity improvements to Hoddesdon Roundabouts (High Leigh development proposals

included in AECOM modelling);

M25 Junction 25 Improvement Option (AECOM modelling); and

M25 Junctions 23-27 Smart Motorway (AECOM modelling).

These were required in order to allow access onto the network for the developments to be 4.3.6included irrespective of any additional highway improvement/mitigation measures provided or

to provide more detailed modelling of existing junctions against which to compare the infrastructure proposals. Schemes marked as AECOM modelling were carried over from the


25

previous round of modelling and considered as committed/completed schemes or essential

for access to development sites.

Demand flow and volume over capacity plots for the Reference Case network are given in 4.3.7

Appendix G. The Volume over Capacity (VoC) plots show any link where the VoC exceeds 85%. This is used to measure where congestion occurs.

As can be seen from the plots, a large number of links in both peak periods exceed 85% VoC 4.3.8by 2033 in the Reference Case indicating a high level of congestion particularly in the

Turnford / Cheshunt areas.

4.4 Task 1: Alternative Junction Treatment at A10 / Church Lane

The different areas of infrastructure to be tested were set out as a number of Tasks. This 4.4.1

allowed each area to be tested independently before combining into a preferred package.

The feasibility and cost associated with the grade separated junction proposed at the 4.4.2A10/Church Lane junction was assessed. This indicated that the proposals were high cost and

that significant risk was associated with the feasibility of construction based on the need for

significant lane restrictions /closures of the A10 required to allow the underpass to be constructed.

As such, a revised at-grade alternative (Scenario 9b) to the proposed underpass (Scenario 4.4.3

8b) at the junction of the A10 and Church Lane was tested. This test was different from the

initial modelling detailed earlier in this document due to the change in modelled forecast traffic growth where lower flows might allow an at grade solution to be achievable.

The proposals tested were based on the AECOM high capacity junctions proposals developed 4.4.4

previously. The junction is a restricted turn signalised junction which maintains the East-West

and North-South movements but bans right turns to maximise the ahead movement throughput. A sketch of the revised proposal is given in Appendix H.

Initial modelling results indicated that although the volume of traffic on the A10 increased 4.4.5

with corresponding decreases on the parallel routes, the VoC ratios were unacceptably high

on the Church Lane approaches in both peaks.

As such, supplementary infrastructure updates were made in order to minimise the VoC on 4.4.6the Church Lane approaches without deterring traffic from the A10. These included an

update of the traffic signal timings at the A10 Church Lane and A10 College Road junctions

and the replacement of the existing mini-roundabout at the Church Lane / High Road, Turnford junction, which provided additional capacity on the northbound approach from

Turners Hill, as illustrated in Figure 1 below. This scenario is referred to as Scenario 9b-5.


26

Figure 1: Location of new Signalised Crossing

Appendix I provides demand flow and VoC plots for the scenario. Difference plots between 4.4.7the Reference Case and this Scenario 9b-5 are also given. These illustrate the rerouting of

traffic onto the A10 with the incorporation of the at grade junction changes. Please note,

where node numbers change, differences cannot be shown within SATURN.

Based on the results above and the cost/feasibility issues around provision of an underpass, 4.4.8it was determined to take forward the high capacity at grade signalised option in conjunction

with the minor roundabout changes to the B156/High Road Turnford junction to the

preferred scenario.

As the introduction of junction changes at A10/Church Lane are fundamental in reducing the 4.4.9traffic on routes parallel to the A10, it was considered most suitable to include the results

from this scenario in all subsequent tests.

4.5 Task 2: Cheshunt Lakeside Development Quantum

A number of development scenarios were tested for the Cheshunt Lakeside site allocation. 4.5.1The impacts of 1,000 and 1,750 houses, and finally 2,000 flats were modelled and their

respective impacts on the network assessed. Between 7,000 to 10,000 sq.m of B1 office use was also included in the assessment.

The trip rates used as part of this task were in line with those set out in Table 5, for housing 4.5.2and flats respectively. A bespoke trip rate for the site was not devised.


27

4.6 Task 3: Fishpools Roundabout

A series of junction improvements were devised by AECOM for the roundabout junction of 4.6.1Winston Churchill Way and Monarch’s Way in Waltham Cross. BBC requested that three of

these options were modelled to assess their relative performance.

Of the AECOM designs, Options 1, 5 & 8 were modelled. These comprised: 4.6.2

Option 1: Signalised junction with east-west priority. Access into Sturlas Way to be

left in, left out only. Access into Swanfield Road maintained. Access out limited to

ahead and left turn movements only.

Option 5: Hamburger roundabout with east-west priority. No access permitted in or

out of Swanfield Road.

Option 8: Realignment of Monarchs Way to the south of the existing junction,

requiring land take and relocation of the existing commercial premises. Signalised

access onto Monarchs Way from separate junctions for Sturlas Way and Waltham

Cross High Street. Swanfield Road access would be via the High Street.

Sketches of the three options are given in Appendix J. The options were included in the 4.6.3

Scenario 9b-5 model (i.e. with at grade solution at A10/Church Lane scenario).

Appendix J also contains demand flow and VoC plots for each option along with difference 4.6.4

plots between the scenarios. The changes in overall Network Statistics for each modelled option from Scenario 9b-5 are given in Table 8 below:

Table 8: Fishpools Options Network Statistics Changes

Option 1 Option 5 Option 8

AM % PM % AM % PM % AM % PM %

Transient Queues -15 -1% -40 -2% 92 4% 153 7% 158 7% 22 1%

Over-capacity Time -146 -9% 25 1% 646 39% 592 20% 881 54% -213 -7%

Link Cruise Time -27 0% 22 0% 51 1% 86 1% 83 1% -1 0%

Total Travel Time -188 -1% 7 0% 788 6% 830 6% 1122 9% -192 -1%

Travel Distance -448 0% 1220 0% 2510 0% 5069 1% 2905 1% -323 0%

Average Speed 0.56 1% 0.07 0% -2.22 -5% -1.79 -5% -3.13 -7% 0.51 1%

As can be seen from Table 8 above and the VoC plots in Appendix J, Option 1 indicates the 4.6.5

most effective solution at the Fishpools junction. Although Options 5 and 8 help to transfer

traffic onto some more strategic routes, this is due to an overall increase in congestion at the junction.

However, following this initial assessment, it was confirmed that Crossrail 2 routing and 4.6.6

subsequent associated additional growth would likely require more significant capacity changes at the junction with further study into the Fishpools junction then required at a later

date. As such, it is unlikely that an interim scheme that would not accommodate the Crossrail


28

2 associated traffic would be constructed as this would likely be considered abortive work. It

was therefore agreed that an interim scheme at Fishpools would not be taken forward to the preferred scenario.

Any interim improvements could prove to be premature and as such BBC intend to produce a 4.6.7detailed Area Action Plan after the adoption of the Local Plan through which to identify the

extent of development opportunities in the area, and the subsequent network improvements

which would be required.

4.7 Task 4: Brookfield & Halfhide Lane

A series of options were devised for the treatment of Halfhide Lane and associated access 4.7.1

arrangements for the Brookfield development. The options for Halfhide Lane included:

Retain Halfhide Lane as an all vehicle through route;

Restriction of Halfhide Lane to public transport as a through route (Option A);

Restriction of Halfhide Lane to public transport as a terminating route from Turnford – this

would effectively be entry into a small bus station; and

Restriction of Halfhide Lane to all vehicles as a terminating route from Turnford – this

would effectively be entry into a small bus station (or a through route for buses) and major car park for Brookfield Riverside.

The first option above is equivalent to Scenario 9b-5. Therefore, the first test carried out was 4.7.2

modelling of the second option labelled Option A. Appendix K provides plots for Task 4

Option A and the differences between these and Scenario 9b-5. It can be seen from the plots, that the closure of Halfhide Lane to non-Public Transport trips resulted in increases in

traffic and VoC at the A10/Turnford, A10/Church Lane and A10/College avenue junctions.

As the latter two of these junctions were key areas of focus for maintaining east-west 4.7.3

connectivity, it was decided to progress to Task 5 to assess the impact of introducing a southbound on slip to the A10 at the Turnford junction to establish whether provision of the

slip would make closure of Halfhide Lane more viable.

4.8 Task 5: Turnford Southern Slip Road

Scenario 9b-5 was updated to include a southbound on slip at the A10 Turnford junction to 4.8.1create an all movements grade separated priority junction (Option B).

Demand flows, V/C and difference plots between this scenario and Scenario 9b-5 are 4.8.2

included in Appendix L. It can be seen that the inclusion of the slip road has very little

impact on the traffic flows in the area. As such, it is unlikely that the cost of the slip road would be warranted by its effect on traffic in the area.

A further test (Option C) combined the closure of Halfhide Lane to private vehicles (Option A) 4.8.3

with the additional of the Turnford slip road (Option B). Model results are also presented in Appendix L.

Option C results in more significant rerouting of traffic to use the Turnford slip road. It should 4.8.4be noted that this Option still results in an increase in trips at College Road and Church Lane

with an associated increase in V/C and that the Turnford junction also shows high levels of V/C on some approaches and further consideration of the operation of this junction should be

considered.


29

It conclusion it is therefore not possible to justify the provision of a southbound slip road at 4.8.5

the Tunford junction. The volume of traffic which would use it would be insufficient to both mitigate impacts elsewhere on the network or justify the cost of a potential scheme.

Increasing the flare widths on selected approached at the Marriott Roundabout were deemed

to be a more effective and economic solution for accommodating southbound access onto the A10 in the area. This alternative mitigation is illustrated in Figure 2.

Figure 1: Marriott Roundabout Capacity Improvements

4.9 Task 6: Old A10

The Broxbourne Transport Strategy aims to reduce journey speeds along the old A10 (A1170 4.9.1/B176). This will be achieved through a range of measures4 but with the overall remit to

make it a more sustainable corridor. The measures to be employed are, at this stage, not

fixed and it is unlikely that they can be modelled directly in the current highway model due to their scale and type.

As such the impact of the journey speed reductions on travel patterns have been modelled by 4.9.2

applying reduced speed limits on the old alignment of the A10 from Waltham Cross through

to Hoddesdon in the north. A speed limit of 20mph has been applied in both directions to all links on this route. Although this is not likely to be the exact measure used, this is intended

to replicate the overall reduction in speed caused by the other measures. Results from the model and comparisons to Scenario 9b-5 are given in Appendix M.

4 There are opportunities to introduce a range of measures to reduce the speed of traffic on the Old

A10. These include a new 20mph speed limit, raised tables at crossing points, reducing the width of

the carriageway to provide wider footways/cycleways, and changing the surfacing of the carriageway for example.


30

The results indicate that the reduction in speed limit causes traffic to reroute from the old 4.9.3

A10 predominantly onto the new A10. This is deemed acceptable and can be accommodated due to the mitigations earmarked for the Church Lane and College Road junctions.

As it is likely that this strategy is likely to be included, the changes in speed limit will be taken 4.9.4through to the preferred option with the caveat that this is likely to make the A10 perform

under more congested conditions.

4.10 Task 7: Junction improvements (off A10)

Indicative designs for three junction improvement schemes were considered for non-A10 4.10.1

junctions in the area, through which to both help regulate the flow of traffic and provide

more capacity, and to improve crossing provision for pedestrians and cyclists. These comprised:

Church Lane / High Street, Turnford signalisation;

Church Lane / Flamstead End Road signalisation;

Goffs Lane / Newgatestreet Road signalisation.

Indicative sketches of each junction are given in Appendix N. The latter of the five schemes 4.10.2

are superseded by the A10 modelling already carried out. As such, the three schemes were coded individually into Scenario 9b-5 based models. Results from the models are also given

in Appendix N.

Each of the three junctions tested cause localised rerouting of traffic and some increases in 4.10.3VoC ratios. This is unsurprising as the provision of pedestrian facilities and traffic signalisation

causes increased delay at the junction to some traffic movements.

The Goffs Lane / Newgatestreet Road and Church Lane / Flamstead End Road impacts are 4.10.4

generally local and not considered to significantly impact the overall network detrimentally. As such, these are recommended for inclusion in the preferred scenario based on their

improvements to pedestrian facilities.

The Church Lane/High Street and Church Lane / Flamstead End Road junctions both provide 4.10.5

better regulation of the flow of traffic in the area. It was therefore deemed that these options

should be included in the preferred scenario. .


31

4.11 Task 8: Preferred Scenario

Using the information above, a preferred scenario was created within the model combining 4.11.1the results from each of the tasks. The data included in this scenario are detailed below.

Scenario 9b-5 which includes the high capacity at grade proposals at the Church Lane 4.11.2

junction as developed as part of Task 1 was used as the starting point. The matrices which

included the higher level of growth at Cheshunt Lakeside from Task 2 were used.

Task 3 option proposals for the Fishpools junction were not included. 4.11.3

The A10/Turnford junction and surrounding area was investigated as concerns were raised as 4.11.4

to the feasibility and cost associated with construction of the proposed Turnford southbound on slip. As such, based on the above Tasks 4 and 5, further review was undertaken to

establish the best solution for the proposed Brookfield development.

The review focused on maximising for highway capacity whilst maintaining the integrity of 4.11.5

the development site, maintaining access to the existing retail developments and to provide a feasible solution for both cost and ability to construct.

The A10/Turnford junction itself had previously been coded as a single node to represent the 4.11.6

grade separated roundabout. This was initially expanded in the model to a multi-node

junction to better reflect each approach based on the size and geometry of the roundabout.

The Brookfield area was updated in more detail based on the Masterplan supplied at the time 4.11.7of modelling. This included a service/access road between Halfhide Lane and the Brookfield

link road to the west of A10/Turnford junction close to and running parallel to the A10. The

proposed A10 southbound on slip was omitted and Halfhide Lane was retained for all vehicles. Initial results showed that the Halfhide Lane/The Links junction could not function

with the increased levels of traffic particularly in the PM peak.

Upgrade of this junction was considered but, due to the constraints of the location of the 4.11.8

existing developments and the level differences, it is unlikely that any upgrade for a four arm all movements junction would be achievable. As such, a number of scenarios for the

Brookfield area were considered. Appendix O contains the layout as agreed with BBC.

The Task 6 Old A10 speed reduction measures were included. Junction improvements for the 4.11.9

three junctions modelled as part of Task 7 were included with the caveat that the Church Lane/High Street junction would need to be analysed to confirm its suitability for inclusion in

the final version of the preferred model.

Prior to any study of the model, BBC advised that the volume of employment at the Park 4.11.10Plaza West development area was to be updated to a 30,000 square metre development size.

As such, the matrices were updated in accordance with the most up to date information.

An initial review of the preferred option was then carried out. A list of the highway schemes 4.11.11

included in this scenario is provided in Table 9. This indicated a need to update the Park Plaza development access junctions based on Linsig traffic signal junction modelling and

adjustment of the A10/Lieutenant Ellis Way traffic signal timings to allow development traffic

to access/egress the sites. The revisions include additional lanes at the A10/Park Plaza south signalised junction. The updated traffic signal Linsig assessment for the Park Plaza area is

given in Appendix P, whilst the layout is illustrated in Figure 3.


32

Table 9: Highway Schemes in Preferred Scenario

Ref: Scheme

HS.01

M25: Capacity improvement at M25 J25, through the provision of a dedicated

left turn lane for northbound traffic off the M25 and the widening of the A10

southbound on its approach to the junction.

HS.02 A10: Modify existing 3-arm junction on A10 to provide an at-grade 4-arm

junction for access into Park Plaza North & West.

HS.03

A10: Provide a ‘hamburger’ style signalised junction with N/S priority at the

intersection of the A10 junction with the A121 Monarch’s Way and B198

Lieutenant Ellis Way (Park Plaza junction).

HS.04 Lieutenant Ellis Way: New 4-arm junction on Lieutenant Ellis Way to the north of

Park Plaza.

HS.05

College Road: At grade improvement at College Road / A10 junction, providing

additional northbound and southbound lanes at the junction and increased

length of northbound left filter into College Road, and banning all right turns.

HS.06

Church Lane: At grade highway capacity improvement at Church Lane / A10

junction, providing an additional north-south lane through the junction and

banning all right turns and left turns onto the A10.

HS.07 Church Lane: Reconfiguration of Church Lane / High Street, Cheshunt

roundabout to provide signalised junction and crossing points for pedestrians.

HS.08 Church Lane: Reconfiguration of Church Lane / Flamstead End Road roundabout

to provide signalised junction and crossing points for pedestrians.

HS.09

Brookfield (Turnford Link Road): Construction of a Halfhide Lane to Turnford

Interchange Link Road, together with provision of a new western arm at the A10

Turnford Interchange.

HS.10

Brookfield (Halfhide Lane Link Road): Construction of new link road immediately

to the west of the A10 providing a link from Halfhide Lane north to Hells Wood,

where it turns westwards to connect to the Turnford Link Road via a new

roundabout, and south to 'The Links' to provide access to Tesco and from the

A10 off-slip.

HS.11 Brookfield (Garden Village Distributor Road): Provision of new distributor road to

serve the new Brookfield development.

HS.12

Brookfield: Reconfiguration of the 4-arm signlaised junction on Halfhide Lane at

junction with The Links and the access road into Brookfield Retail Park, by

removing access to/from The Links and allowing only movements into (and not

out of) the Retail Park.

HS.13 Brookfield: Provision of additonal capacity at Marriott Roundabout.

HS.14

Goffs Lane: Reconfiguration of Newgatestreet Road / Cuffley Hill / Goffs Lane

junction give way to provide signalised junction with crossing points for

pedestrians.

HS.15 Dinant Link Road: New roundabout on Dinant Link Road to permit access into

High Leigh development.

HS.16 Dinant Link Road: Sun roundabout improvements (junction of Dinant Link Road


33

Ref: Scheme

and Ware Road) to provide additional lane on eastbound arm of roundabout.

HS.17

Hertford Road: Hertford Road / Ware Road roundabout improvements to

provide additional eastbound and southbound lanes at respective arms of the

junction.

HS.18 Essex Road: Provision of new Essex Road Bridge.

HS.19 Essex Road: Improvements to roundabout at junction with Dinant Link Road.

HS.20 Signage: Update the network signage across the Borough to reflect the new

access arrangements on/off the A10 at Church Lane.

HS.21 Secondary School Access: Provision of a new access into the secondary school

site from the A10 spur road to the south.

HS.22 Secondary School Access: Provision of a new access into the secondary school

site from Church Lane to the north.

Figure 3: Park Plaza Junction Layout


34

In additional to the above changes, the Turners Hill/Windmill Lane traffic signal timings were 4.11.12

updated to improve flows in this area.

Initial review of the model was carried out and, as discussed previously, the Church 4.11.13

Lane/Turners Hill junction was found to operate below acceptable levels. Therefore, additional widening on each approach to provide flaring to two lanes at the stop lines for

each approach was assumed. This allows the junction to operate with higher capacity and is

likely to be achievable within the highway boundary based on aerial mapping observations. Further investigation of this option will be needed to confirm that this option is feasible.

It was also understood that trips related to an employment site closure had not been 4.11.14

removed from the Cheshunt Lakeside zone. Previously, part of the Cheshunt Lakeside site was occupied by Tesco offices prior to 2014 and hence the trips associated with these offices

were included in the 2013 base year model although they are no longer on the site.

Therefore, the removal of these trips needed to be factored into the forecast matrix building as this is between 2013 and the forecast year not the current year and the forecast year.

The trip end reduction for the Tesco closure were calculated. These trip end adjustments 4.11.15

were updated in the matrix building process and assigned to the networks for both the

Reference Case and Preferred Scenario models.

Results from the final models are given in Appendix Q. 4.11.16

4.12 Comparisons with the Base Year

Following the identification of the preferred scenario as the most effective package of 4.12.1measures its performance was assessed against the base year model.

Key indicators of network performance are travel times across the network. Comparison was 4.12.2

therefore made with regard to the length of journey times between set points within the

authority.

The comparative journey times identified within the base year, reference case and do 4.12.3something scenarios are detailed in Table 10 overleaf. The routes have been chosen to

illustrate the main north south movement via the A10 and also focuses on east west connectivity.

The comparative journey times highlight that: 4.12.4

With the preferred package of mitigations in place, journey times will be broadly similar

(albeit slightly slower) to those in the 2013 base year on most routes; The exception to this is the Park Plaza > Waltham Cross link;

Journey times with mitigations in place are significantly lower than those in the reference

case scenario in which growth comes forward but no mitigations are provided; and

In this respect, significant time savings can be seen across the board, again with the

exception of the Park Plaza > Waltham Cross link.

Based on the above results, it is considered that the proposed package of highway measures 4.12.5

suitably mitigate the impact of the Local Plan development traffic.


35

Table 10: Journey Time Comparison

2013

NB 09:30 10:35 10:58 09:43 01:05 01:28 00:13 -00:52 -01:15

SB 09:32 10:25 25:47 12:31 00:53 16:15 02:59 02:06 -13:16

NB 10:29 12:34 26:13 12:28 02:05 15:44 01:59 -00:06 -13:45

SB 09:37 09:55 11:29 09:41 00:18 01:52 00:04 -00:14 -01:48

EB 05:46 06:22 07:25 06:47 00:36 01:39 01:01 00:25 -00:38

WB 05:51 06:04 07:29 07:09 00:13 01:38 01:18 01:05 -00:20

EB 05:13 05:45 06:18 06:13 00:32 01:05 01:00 00:28 -00:05

WB 06:03 09:07 13:38 07:29 03:04 07:35 01:26 -01:38 -06:09

EB 05:27 06:01 13:57 07:43 00:34 08:30 02:16 01:42 -06:14

WB 05:13 07:51 12:27 13:51 02:38 07:14 08:38 06:00 01:24

EB 05:55 04:59 05:41 07:42 -00:56 -00:14 01:47 02:43 02:01

WB 06:14 10:12 20:14 12:53 03:58 14:00 06:39 02:41 -07:21

EB 06:41 07:25 09:19 08:02 00:44 02:38 01:21 00:37 -01:17

WB 05:48 06:27 22:13 09:21 00:39 16:25 03:33 02:54 -12:52

EB 07:09 06:52 08:26 09:02 -00:17 01:17 01:53 02:10 00:36

WB 06:44 10:14 13:28 06:52 03:30 06:44 00:08 -03:22 -06:36

EB 09:37 09:47 10:39 09:39 00:10 01:02 00:02 -00:08 -01:00

WB 10:06 10:44 13:55 10:54 00:38 03:49 00:48 00:10 -03:01

EB 10:23 10:49 12:31 10:41 00:26 02:08 00:18 -00:08 -01:50

WB 11:23 14:13 17:44 10:47 02:50 06:21 -00:36 -03:26 -06:57

Between Goffs

Oak and Cheshunt

Station

AM Peak

PM Peak

Between Park

Plaza

development and

Waltham Cross

Station

AM Peak

PM Peak

Between Park

Plaza

development and

Cheshunt Station

AM Peak

PM Peak

Between

Brookfield

development and

Cheshunt Station

AM Peak

PM Peak

Journey Times (minutes:seconds) 2033

A10 between M25

J25 and A1170

(Dinant Link Road,

Hoddesdon)

AM Peak

PM Peak

Do Minimum (No Local

Plan Growth or

Mitigation)

Differences

Route Period Direction Base Model

No Mitigation (Local

Plan Growth without

mitigation)

Local Plan Growth

with Preferred

Mitigation

Difference Base

Model & 2033 Do

Minimum

Difference Base Model

& Preferred Mitigation

Difference No

Mitigation & Preferred

Mitigation

Difference Do

Mimimum & Preferred

Mitigation

Difference Base

Model & Local Plan

Growth without

mitigation


www.wyg.com creative minds safe hands 36

4.13 Wider Impacts

The impact of the preferred package of measures on the wider highway network were 4.13.1

subsequently tested through the use of Hertfordshire County Council’s COMET model. This assessment was undertaken in May 2017 and generated the following conclusions:

Epping Forest

The main links between Broxbourne and Epping Forest to the east are via the A121 which 4.13.2

connects Waltham Cross to Waltham Abbey and beyond, Nazeing New Road which links the town of Broxbourne with Nazeing, and Essex Road which accommodates traffic entering the borough

from the Harlow area.

Lower Nazeing: COMET modelling highlighted that by 2031 Lower Nazeing would be

suffering from delays in the centre of the village and on approaches to it, without the additional growth proposed within the Broxbourne Local Plan. When the Local Plan

growth and associated transport mitigations are considered, it highlighted a decrease in

the volume of traffic on Lower Nazeing Road in the AM and PM peaks, together with the inter-peak peak. Despite this, the overall level of delay with Lower Nazeing would

remain the same.

Waltham Abbey: In terms of the A121 through Waltham Cross and Waltham Abbey,

the COMET modelling suggests that there will be little difference in the volume of traffic

along the east-west corridor with or without the Local Plan allocated growth coming forward. Delays under both scenarios are estimated to be around the 30-90 seconds

mark in the PM peak at the Highbridge Retail Park junction.

Essex Road: Flows into and out of Hodedesdon via Essex Road and Dobbs Weir Road

to/from Harlow are envisaged to increase as a consequence of the growth earmarked

to come forward through the Broxbourne Local Plan. However these increases in both directions in the morning and evening peaks, are not expected to see a material change

in the level of delay experienced by road users.

As the proposed terminus for Crossrail 2 services, Broxbourne will have an increasing role to play 4.13.3as a focus for more strategic rail based trips. Likewise, Waltham Cross Station is also likely to

grow in popularity for trips into the capital. Both will draw in additional trips from Epping Forest,

the impact of which will require further consideration.

The designation of Harlow as a Garden Town will see significant growth within Epping Forest, 4.13.4East Hertfordshire and Harlow itself with around 20,000 new dwellings set to come forward as

part of the growth ambitions of the authorities. The impact of this on the north of Broxbourne

will have to be determined through detailed modelling led by these neighbouring authorities.

East Hertfordshire

East Hertfordshire sits to the north of Broxbourne and the A414 through the towns of Hertford 4.13.5

and Ware forms an important east-west link which connects to the A10 immediately to the north

of Hoddesdon. The urban areas of Ware and Hertford are also continuous with Hoddesdon and as such there are a lot of movements between the towns.

Despite this it is not anticipated that there will be a tangible difference in the volume of trips on 4.13.6

the A10 and A414 in 2031 scenarios. Likewise, delays of over 5 minutes are expected to occur in the centre of Hertford in 2031 with or without development within Broxbourne being provided.



The COMET model fact indicates volumes on the A10 and A414 will decline as a consequence of Broxbourne growth and subsequent mitigation proposals albeit only marginally.

Enfield

Enfield, to the south of Broxbourne and the M25, is accessed via the A10 and the A1010 4.13.7

(Monarchs Way / Hertford Road). Delays are expected to be experienced on the road network in Enfield in 2031 with or without Broxbourne related growth where the A10 and A1010 meet

Bullsmoor Road.

These delays in the morning and evening peaks are anticipated to be between 30-90 seconds at 4.13.8

each junction and changes to the transport network in Broxbourne associated with new developments at Park Plaza and in Waltham Cross are not the cause this congestion according to

the COMET modelling undertaken.

Welwyn Hatfield

Within the borough of Welwyn Hatfield to the west of Broxbourne, Cuffley Station provides a link 4.13.9into London for many residents of the Goffs Oak area of West Cheshunt. The B156 links the two

settlements and in a 2031 scenario and both east and west bound flows in the morning peak period are anticipated to reduce significantly compared to the Local Plan ‘Do Minimum’ scenario,

as a result of the transport mitigations associated with growth coming forward through the Broxbourne Local Plan.

In the evening peak, the picture differs slightly. Whilst westbound traffic into Cuffley is also 4.13.10expected to reduce with growth and mitigations in place, eastbound traffic into Goffs Oak is seen

to increase in the results of the COMET modelling assessment.

Wider Network / Strategic Trips

In terms of the Strategic Road Network (SRN), the model suggested that the capacity 4.13.11improvements on the A10 are not such that strategic trips from the A1 or M11 will reassign onto

the A10 itself. This will ensure that traffic is not drawn in from the wider network with the negative implications it would have generated for the borough.

5. Summary

This technical note sets out the process through which the Broxbourne Highway Model has been 5.1.1

applied to develop a sound and robust evidence base to support the Broxbourne Transport

Strategy.

It has considered a number of alternative scenarios in terms of the level of development to be 5.1.2provided, the scale of future traffic growth, and the mitigations through which to accommodate

the increase in demand to travel in and around Broxbourne in the period up until 2033.

The results this process has generated should not be viewed in isolation. It has informed further 5.1.3

and more strategic multi-modal modelling of the transport network through the Hertfordshire COMET model. In addition, at a more local level, it will inform more detailed micro-simulation

modelling of specific junctions through which specific designs can be refined.



Contact: Planning Policy Team

t. 01992 785 555

e. [email protected]

mailto:[email protected]