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A355 Route Enhancement Appraisal Specification Report Slough Borough Council

3 October 2014

A355 Route Enhancement Appraisal Specification Report

Atkins A355 Route Enhancement Appraisal Specification Report | Version 1.0 | 3 October 2014 | 5134791 ii

Notice

This document and its contents have been prepared and are intended solely for Slough Borough Council’s information and use in relation to the application for funding from the Berkshire Local Transport Board.

ATKINS assumes no responsibility to any other party in respect of or arising out of or in connection with this document and/or its contents.

This document has 36 pages including the cover.

Document history

Job number: 5134791 Document ref:

Revision Purpose description Originated Checked Reviewed Authorised Date

Rev 1.0 Draft report SP DW 01/10/14

Rev 2.0 Final report SP PS DW AC 03/10/14

Client signoff

Client Slough Borough Council

Project A355 Route Enhancement

Document title A355 Route Enhancement Appraisal Specification Report

Job no. 5134791

Copy no. 1

Document reference

Final


Atkins A355 Route Enhancement Appraisal Specification Report | Version 1.0 | 3 October 2014 | 5134791 iii

Table of contents

Chapter Pages

1. Introduction 1

Purpose of the report 1

Project summary 1

Objectives of the scheme 2

Project programme 2

2. Challenges and issues 3

Strategic fit 3

Key issues 3

Outcomes of the scheme 3

Options considered 3

Partner organisations 4

Expected outcomes 4

Deliverability and risks 5

3. Transport modelling 6

The existing modelling framework 6

Local and current year validation 8

Proportionality of modelling approach 10

The proposed approach 11

4. Appraisal methodology 13

Economic appraisal 13

Distributional Impacts (DIs) 15

Environmental scoping 15

5. Appraisal Specification Summary Table 29

Appendix 31

Appendix A. Scheme drawing 32

Tables Table 2-1 Project risks and mitigating actions 5

Table 3-1 Base year - highway journey time validation AM, IP, PM modelled and observed 7

Table 3-2 A355 Tuns Lane/Church St. Roundabout Flow Comparison (vehicles) 9

Table 3-3 A4 Bath Road/ A355 Tuns Lane Flow Comparison (vehicles) 10

Table 3-4 Journey Time Comparison on A355 (seconds) 10

Table 4-1 Risks for air quality 20

Table 4-2 Risks for greenhouse gases 22

Table 4-3 Likely ecology impacts of the scheme in construction and operation 26

Figures Figure 1.1 Scheme overview 1

Figure 4.1 Assessment matrix 16


Atkins A355 Route Enhancement Appraisal Specification Report | Version 1.0 | 3 October 2014 | 5134791 1

1. Introduction

Purpose of the report 1.1. ‘The Transport Appraisal Process’ as stated in Section 2.12.2 of the Department for Transport

(DfT)’s Transport Appraisal Guidance (TAG) states that an Appraisal Specification Report (ASR) should be submitted to set out how appraisal will be undertaken. It should detail the:

• Proposed approach to modelling and forecasting;

• Proposed methodology for assessing each of the sub-impacts presented within the AST;

• Proposed level of design or specification which will inform the cost estimation, and how better cost information will be obtained; and,

• Evidence that views on the appraisal methodology have been sought from the statutory environmental bodies and others.

This report discusses the overall methodology that is to be followed to appraise the A355 Route Enhancement scheme.

Project summary 1.2. The A355 is a key arterial road that links the M40 Junction 2 with the M4 Junction 6 and provides

access to the Slough Trading Estate and Slough town centre, and also intersects with the A4. Between the junctions of the A4 and the M4, the A355 Tuns Lane includes a conventional four-arm priority controlled give-way controlled roundabout, known locally as the Copthorne Roundabout. The roundabout has four approaches and exits which consist of the A355 Tuns Lane north and south arms; Church Street to the east and Cippenham Lane to the west.

1.3. The proposed A355 Route Enhancement project involves converting the junction from give-way control on all arms to a signalised ‘hamburger’ style roundabout. The north-south (A355 Tuns Lane) movements will be prioritised to cut across the circulatory carriageway whilst a flare will be provided on the southern arm to allow for left-turning traffic to bypass the junction. To the south of the junction the southbound carriageway will be widened to three lanes from the Copthorne Roundabout through to J6 of the M4 including across Chalvey High Street Bridge.

1.4. A scheme overview in the context of the surrounding highway network is shown on Figure 1.1 whilst the proposed layout of the preferred scheme is indicated in Appendix A.

Figure 1.1 Scheme overview



Objectives of the scheme 1.5. The objectives of the scheme, as identified in the Option Assessment Report, are as follows:

• Improve access to employment centres, Slough Town Centre and Cippenham thereby supporting economic and population growth in Slough;

• Alleviate the severe congestion on the A355 by allowing better flow of traffic;

• Minimise the impact of noise and air pollution and greenhouse gases on the A355 corridor; and

• Improve operation of the A355 Tuns Lane.

Project programme 1.6. Milestones for project delivery are given in section 2.13.



2. Challenges and issues

Strategic fit 2.1. A key objective of the Thames Valley Berkshire’s Strategic Economic Plan is to improve urban

connectivity by linking residential areas to mainline railway stations, employment, leisure, learning and retail centres. Improvements to north-south routes through the area to link the M40, M4 and M3 are a key aim of the Thames Valley Berkshire Local Enterprise Partnership.

Key issues 2.2. Slough, which is close to the M4, M25, Heathrow Airport and the employment areas of West

London, experiences traffic volumes beyond anything a town of its size would normally generate, including conflicting peak hour flows of inward and outward commuting patterns. This causes severe congestion and leads to long delays on the network thereby reducing economic efficiency. The Copthorne Roundabout on the A355 in particular, is considered to be a major bottleneck on the network between the commercial, employment and residential areas within Slough and the M4 motorway.

2.3. Councils have shown that the UK AQS objective and EU limit value thresholds most likely to be exceeded are for annual mean NO2 are due to road traffic emissions. The A355 from junction 6 of the M4 motorway to the A4 Bath Road is incorporated in Slough’s Air Quality Management Area (AQMA) number 3. Air quality in the AQMAs are monitored and reported by Slough Borough Council against the annual mean NO2 UK AQS objective and EU limit value thresholds.

Outcomes of the scheme 2.4. The A355 Route Enhancement scheme will reduce congestion on a key transport route for

commuting and economic activity as it is the primary means of accessing the M4 to the south for vehicles using the Slough Trading Estate, the largest business park in Europe. The scheme’s positive impact on congestion and journey times should also reduce the environmental disbenefits generated by vehicle traffic within the AQMA. The proposal to improve the A355 Tuns Lane will:

• Improve frequency, journey times, reliability and journey quality for all road users;

• Improve accessibility and affordability;

• Reduce casualty frequency and severity;

• Reduce congestion and its environmental impacts; and

• Enhance the viability of the town centre and other key areas.

Options considered

Consequences of do nothing 2.5. If the status quo is retained as overall travel demand increases with natural background growth

there will likely be increasing road congestion and delay leading to further increases in economic inefficiency. Economic competitiveness will be lost and new developments, including regeneration projects, may not take place as investors look elsewhere. Local businesses which are already affected by increased journey times could be persuaded to relocate. Local air quality will continue to worsen in line with congestion whilst residents on nearby roads will be adversely affected (due to traffic taking inappropriate alternative routes to avoid congestion).

Options considered 2.6. High level options considered in the Option Assessment Report were:

• Highway layout changes as per A355 Route Enhancement scheme description;



• Highway layout changes to the Copthorne Roundabout only;

• Demand management measures; and

• Traffic management measures.

2.7. Early variations on the proposed highway layout changes included signalising the roundabout in its current layout, known as the ‘Eton scheme’ due to the source of S106 money that would help fund it; and creating a signalised crossroads junction. Modelling of each of these options, along with the preferred ‘hamburger’ design, took place in 2013 using the signalised junction modelling software LinSig and has shown that the ‘hamburger’ design resulted in providing the optimal level of capacity. The signalised crossroads did not resolve the capacity problems experienced by the heavy peak hour north-south movements at the roundabout and would cost substantially more than the ‘hamburger’ option (accounting for the civil engineering work required on the junction alone).

2.8. The formation of the preferred option has been driven by guiding design principles aimed at ensuring there is genuine potential for a robust business case which recognises that the corridor features significant traffic levels. These guiding principles effectively result in a scheme that is infrastructure and impact light, but looks to enhance journey time performance for general traffic at least cost. An outline assessment of economic viability for the preferred option was undertaken in October 2013 and identified a BCR of 10.1

2.9. The core elements of the preferred scheme are given below and relevant drawings are shown in Appendix A:

• Conversion of the roundabout to a ‘hamburger’ design with the north-south (A355 Tuns Lane) movements, two lanes northbound and three lanes southbound, altered to cut across the circulatory carriageway. The circulatory section will be retained for the side roads (Cippenham Lane and Church Street), with Church Street remaining as a give-way controlled arm;

• Installation of MOVA controlled signals on three approaches to the roundabout: A355 Tuns Lane north; A355 Tuns Lane south; and Chippenham Lane. Church Street to remain unsignalised;

• Widening to the south-east corner of the roundabout to allow a 3-lane southbound exit and to the subsequent southbound carriageway to continue 3-lanes between the Copthorne roundabout and J6 of the M4, including across Chalvey High Street Bridge;

• Reduced speed limit on the A355 Tuns Lanes south of the roundabout to 30mph; and

• Resurfacing of the carriageway and renewal of drainage, lighting, signage and lineage throughout.

Partner organisations 2.10. The partner organisations involved in and committed to supporting the project to improve

connectivity are:

• Thames Valley Berkshire Local Enterprise Partnership;

• SEGRO development;

• Heathrow Airport Ltd; and

• Royal Borough of Windsor and Maidenhead.

Expected outcomes 2.11. The A355 Route Enhancement scheme will deliver a major contribution to reducing road

congestion and increasing economic efficiency and business confidence. This project will support the delivery of the 150,000m2 of office and ancillary space proposed in the Slough Trading Estate master plan and over 60,000m2 of office space, 2,300 dwellings and other development to be delivered in the town centre as part of the ‘Heart of Slough’ project.



Deliverability and risks 2.12. All of the land required for scheme is already in Slough Borough Council (SBC) ownership and

committed for highway adoption. Developer contributions have been secured through S106 agreements. Risks to the project will be fully explored through a risk workshop with key stakeholders.

Key project milestones 2.13. The key milestones for this project are as follows:

• Business Case ready for submission to independent assessor: October 2014;

• Conditional approval sought from Berkshire Local Transport Board (BLTB): November 2014;

• Tendering process begins: Feb 2015;

• Works begin on ground and will be coordinated with delivery of Slough Mass Rapid Transit (SMaRT) scheme: June 2015;

• Completion works: June 2016.

Principal risks and mitigation actions 2.14. Risks are limited by the fact that all of the works will take place on existing highway land. Risks

and their mitigation measures are described in Table 2-1.

Table 2-1 Project risks and mitigating actions

No. Risk Likelihood (H/M/L)

Severity (H/M/L)

Mitigating actions

1 Reduced funding from delay (or loss) of developer funding

L L Local Authority funds will be made available if S106 is not delivered within timescales

2 Increased cost due to design changes or additional works required to strengthen Chalvey High Street Bridge (currently scheme is at preliminary design stage)

M H If bridge requires strengthening this will be partly covered by Local Authority maintenance budgets

3 Higher than expected costs M M Scheme to be tendered with other major projects included within the SEP to provide VfM

4 Delays in procurement process L M Programme allows sufficient time for process

5 Delays and/or increased costs due to utility requirements (currently scheme is at preliminary design stage)

M M Close dialogue and planning with utility companies



3. Transport modelling

The existing modelling framework 3.1. Atkins developed a multi-modal model framework for Slough Borough Council (SBC) in 2009.

The Slough Multi-Modal Transport Model (SMMTM) framework has a 2009 base year and contained the following elements:

• A highway assignment model in SATURN;

• A public transport assignment model in EMME;

• A WebTAG compliant demand model in EMME; and

• A DIADEM model for assessing the impact of highway interventions.

3.2. The base year highway SATURN model has the following modelling characteristics:

• A total of 341 zones, covering the UK;

• Three time periods, AM peak (08:00-09:00), average Inter Peak hour (10:00-16:00) and PM peak (17:00-18:00); There are also one hour pre-peak periods for both AM and PM peak operated by PASSQ function within SATURN; and

• Five modelled user classes, including, car employer business, car commuting, car other, LGV and HGV.

3.3. The base year demand has come from a variety of sources such as Road Side Interviews, journey to work census and school data. The SATURN highway assignment model has been calibrated and validated following DMRB’s and latest WebTAG guidance. This is fully documented in a Local Model Validation Report (LMVR) issued to Slough Borough Council in January 2011.

3.4. The Public Transport Assignment Model is EMME based and includes bus and rail modes. The demand is based on specifically collected bus and rail passenger interview survey data and other supplementary datasets such as bus Electronic Ticketing Machine (ETM) and rail NRTS. The model was calibrated and validated in line with guidance.

3.5. The A355 Route Enhancement scheme aims to improve traffic condition on the strategic north-south A355 route between the M4, Slough Trading Estate and the M40 and also improve access to Slough town centre. As a result, it is expected that the scheme will generate significant journey time savings for motorists and journey time will be a key element to estimating user benefits which will underpin the Business Case.

3.6. The LMVR indicates good parity between model and observed highway journey times on the A355 and A332, as shown in Table 3-1, except for the PM peak in the southbound direction on A355. The base year flow validation along A355 and A4 Bath road has also been checked and is generally satisfactory both at screenline level or on individual links as reported in the LMVR report.



Table 3-1 Base year - highway journey time validation AM, IP, PM modelled and observed

Route Number

Route Description

Direction Route Journey Time Diff in seconds

% Diff Within 15%

(or 60secs if higher)

Observed Modelled

AM Peak (08:00-09:00)

Route 2

A355/ A322 Woodham Rd to Farnham Rd

NB 00:13:18 00:12:11 -67 -8% �

SB 00:13:13 00:13:34 21 3% �

Route 5

A332 to Grays Park Rd/ Dutfield Park

NB 00:11:27 00:10:31 -56 -8% �

SB 00:11:52 00:12:24 32 4% �

Inter Peak (average 10:00-16:00)

Route 2


NB 00:09:42 00:09:03 -39 -7% �

SB 00:10:06 00:08:56 -70 -12% �

Route 5


NB 00:10:00 00:09:26 -34 -6% �

SB 00:09:45 00:10:16 31 5% �

PM peak (17:00-18:00)

Route 2


NB 00:12:16 00:11:48 -28 -4% �

SB 00:14:06 00:11:17 -169 -20% �

Route 5


NB 00:11:41 00:11:07 -34 -5% �

SB 00:13:02 00:12:31 -31 -4% �

3.7. In June 2014, Atkins was commissioned by Slough Borough Council to test The Slough Mass Rapid Transit (SMaRT) scheme by using the SMMTM models. The scheme proposed includes two phases; Phase 1, the western section of the route and Phase 2, the central section. The western section to include eastbound segregated bus lanes fronting Slough Trading Estate. The central section to include bus lanes and other priority measures between the estate, Slough town centre and eastwards to Junction 5 of the M4.

3.8. The SMMTM SATURN and Public Transport models were subsequently updated to assess the SMaRT. The key model updating works included:

• A total of 363 zones, including 22 new zones representing the new developments in the Borough;

• Do Minimum and Do Something models for the forecasting year of 2015 and 2025;

• Fixed assignment for Highway and Public Transport model assignment as the impact of the scheme is likely to be exclusively to bus passengers; and

• A simplified method of estimating induced bus demand was conducted in the sensitivity tests using elasticities.

3.9. The ‘Do Something’ models in the recently tested SMaRT will serve as the ‘Do Minimum’ scenario for A355 Business Case as SMaRT is a committed scheme. The SMaRT scheme



comprises some off-line dedicated bus lanes, the improvements of signal timing through MOVA and stack capacity increase for left turns at the TESCO and Sainsbury junctions.

3.10. Traffic forecasts for the Business Case will be produced for the opening year (assumed as 2017) and a post-opening future year (2027, 10 years from completion), for the ‘Do Minimum’ and ’Do Something” scenarios for three peak time periods, e.g. AM (08:00-09:00), IP (average 10:00-16:00) and PM (17:00-19:00). Due to relatively small time lag of 2 years between SMaRT and A355 Business Case, it can be assumed that the highway network supply for A355 Business Case will be identical to that for SMaRT, as well as the development assumptions for both opening and post-opening forecasting years.

3.11. Accordingly, the highway trip matrices for the testing the A355 Route Enhancement scheme in year 2017 and 2027 will be produced by TEMPRO (database 6.2) growths for car demand and National Traffic Forecast (year 2013) for LGV and HGV from 2015 to 2017 and 2025 to 2027 respectively. The income and fuel adjustments will be applied on TEMPRO growths.

3.12. The major developments included in the Slough SMaRT models are:

• The Heart of Slough (residential, Thames Valley University, land of the Old Library and offices at the bus station);

• SIFE and LRCC2;

• Cippenham Phase 4 and Phase 5;

• Kennedy Park;

• Castleview;

• Linden Homes;

• Asphalt Plant; and

• Colnbrook Logistics centre and Horton Quarry which were operational when considered for the SMaRT Do Minimum, but the traffic, mostly HGV, is primarily between the site and Heathrow airport.

Local and current year validation 3.13. The SMMTM assignment model (which has a base year of 2009) covers three time periods for a

typical weekday consisting of an AM Peak (08:00-09:00), Inter-peak (10:00-16:00) and PM Peak (17:00-18:00). Ideally, 2014 would be used as the base year; and current year validation would be undertaken whereby a model forecast for 2014 is compared to the current situation. Forecasts can then proceed from 2014 as a more current base year, as opposed to 2009. However, there is insufficient data to progress this validation in terms of inputs such as demand, traffic data, and the time required would pose a major risk to delivery.

3.14. Meanwhile, it is worth noting that there have been some major changes for the local highway network since 2010, such as the Chalvey Way One-Way scheme, junction improvements for the regeneration of the Heart of Slough Scheme, and the A4 Bath/M4 Spur roundabout improvement. Consequently, there will be traffic rerouting or redistribution in Slough, which normally takes time to settle. In recognition of this, some preliminary comparisons in journey time and link flows along the A355 have been undertaken in order to have a better understanding of the traffic condition changes since 2009.

3.15. Table 3-2 and 3-3 show the entry arm flow comparisons (for AM and PM peak) between the traffic counts collected in May 2010 (as used for base year model development) and in June 2013 for A335 Turns Lane/Church Street roundabout and A4 Bath Road/A355 Tuns Lane respectively. It can been seen that for both junctions, although the change for the total entry demand appears to be sensible, there are substantial traffic redistributions across the entry arm, especially for Church Street and Cippenham Lane which both reveal a significant flow decrease; most probably due to the to the introduction of the Chalvey Way One-Way scheme.



3.16. These local traffic distributions, along with the impacts of the natural background traffic growth, have substantial impacts on travel time along local key routes. It has been found that the journey time between A355/B3026 Eton Wick Road and A355/Sheffield Road increases from 8% to 35% across each of the three time periods from 2009 to 2014, as shown in the Table 3-41.

3.17. The flow and journey time comparisons between the base year 2009 and 2014 reveal that there are some significant changes in local travel conditions. It is therefore critical that rigorous examinations are required for comparing model outputs against traffic data such as counts and journey time where available. Sense checks on traffic routing are also necessary to ensure the travel patterns are realistic.

3.18. WebTAG guidance will be used to examine the modelling outputs and remedy measures will be undertaken if the outputs fail to meet the necessary WebTAG criteria.

Table 3-2 A355 Tuns Lane/Church St. Roundabout Flow Comparison (vehicles)

May 2010 June 2013 Difference

AM(8-9) Car LGV HGV Total Car LGV HGV Total Car LGV HGV Total

A355Tuns Lane SB to M4 981 172 57 1210 1279 175 95 1549 30% 2% 67% 28%

Church St WB 532 56 12 600 321 34 11 366 -40% -39% -8% -39%

A355 Tuns Lane NB to Town Centre 2372 203 72 2647 2504 174 79 2757 6% -14% 10% 4%

Cippenham Lane EB 470 53 11 534 397 46 13 456 -16% -13% 18% -15%

Total Arms 4355 484 152 4991 4501 429 198 5128 3% -11% 30% 3%

PM (17-18) Car LGV HGV Total Car LGV HGV Total Car LGV HGV Total

A355 Tuns Lane SB to M4 1304 109 18 1431 1520 102 35 1657 17% -6% 94% 16%

Church St WB 345 41 5 391 237 16 2 255 -31% -61% -60% -35%

A355Tuns Lane NB to Town Centre 1619 191 45 1855 1837 206 54 2097 13% 8% 20% 13%

Cippenham Lane EB 1028 65 7 1100 622 41 12 675 -39% -37% 71% -39%

Total Arms 4296 406 75 4777 4216 365 103 4684 -2% -10% 37% -2%

1 Note that the 2009 journey time data was collected by traditional moving observed car method whereas the 2014 was obtained from TomTom database. Therefore there will be some discrepancies related to the sample size and data accuracy between the two data sources.



Table 3-3 A4 Bath Road/ A355 Tuns Lane Flow Comparison (vehicles)

May 2010 June 2013 Difference

AM(8-9) Car LGV HGV Total Car LGV HGV Total Car LGV HGV Total

A355Tuns Lane SB to M4

725 105 29 859 689 98 50 837 -5% -7% 72% -3%

A4 Bath Road WB

1168 111 24 1303 1430 122 56 1608 22% 10% 133% 23%

A355Tuns Lane NB

1533 140 54 1727 1577 119 67 1763 3% -15% 24% 2%

A4 Bath Road EB

560 101 24 685 652 77 35 764 16% -24% 46% 12%

Total Arms 3986 457 131 4574 4348 416 208 4972 9% -9% 59% 9%

PM (17-18) Car LGV HGV Total Car LGV HGV Total Car LGV HGV Total

A355Tuns Lane SB to M4

774 88 17 879 596 51 19 666 -23% -42% 12% -24%

A4 Bath Road WB

1354 86 9 1449 1340 75 13 1428 -1% -13% 44% -1%

A355Tuns Lane NB

940 106 25 1071 891 96 38 1025 -5% -9% 52% -4%

A4 Bath Road EB

867 56 9 932 1258 65 15 1338 45% 16% 67% 44%

Total Arms 3935 336 60 4331 4085 287 85 4457 4% -15% 42% 3%

Table 3-4 Journey Time Comparison on A355 (seconds)

2009 Survey 2014 TomTom Difference

Direction From To AM IP PM AM IP PM AM IP PM

NB A355/B3026 A355/Sheffield Rd

613 379 478 786 410 501 173

(28%)

31

(8%)

23

(5%)

SB A355/Sheffield Rd

A355/B3026 476 313 552 539 424 692 63

(13%)

111

(35%)

140

(25%)

Proportionality of modelling approach 3.19. The analysis in the previous sections has demonstrated that the SMMTM validates reasonably

well in the area of interest, both in terms of flows and journey times. But it was also observed that there are some significant changes between 2009 when the model was developed, and the current situation. However, it should be noted that the changes are largely the traffic reassignments in response to local traffic management schemes rather than people’s travel pattern or choice changes, as concluded from the SMaRT project.

3.20. Section 3.2 of WebTAG (Unit T) discusses the concept of proportionality in model design. Below is a summary of the salient points in that section that need to be considered.

3.21. The Unit states2 that the most appropriate modelling approach will depend on the type of scheme, the circumstances, its objectives and the stage of the appraisal and decision making process. In the early stages when the best transport options to solve the identified problems are examined, more light-touch methods may be appropriate. That said, one must ensure that the

2 Para-phrasing



indications from such models do not give rise to unrealistic expectations of benefits that are unlikely to result from a full modelling approach.

3.22. For highway schemes, WebTAG recommends that ‘the potential impact of induced traffic should be recognised and it is highly recommended to scope the need for a demand model at an early stage..’. In the case of public transport schemes, much of the patronage will be extracted from existing public transport services, and a public transport assignment model provides information on the potential viability of the scheme. In later stages of scheme development, WebTAG states that a fully specified appraisal and the proportionality of the modelling approach will need to be discussed in the ASR.

3.23. WebTAG discusses the trade-offs between model complexity and constraints on resource, data requirements and expertise. In general, the model design will depend on the nature of the problem and their likely solution, the size of the study area, the number of options to be tested, data availability and the need to update models and conduct new surveys, timescale for model development; and finally the required accuracy of the recommendations.

3.24. The WebTAG Unit states that the scheme scope may not necessitate a "full" modelling specification in some circumstances. For example, ‘..a bus priority strategy aimed primarily at providing a better level of service for existing bus passengers with no effect on other modes may require only a public transport supply (assignment) model to provide the necessary inputs to a relatively simple appraisal…’

3.25. In view of the WebTAG guidance, a fixed highway assignment approach is proposed for the A355 Route Enhancement Business Case tests, based on the following evidence or findings:

• The SMMTM demand model takes considerable time to set up and operate, which doesn’t fit in the work program and timescale;

• At present there is no bus operated on A355 between A4 Bath Road and M4 except for a small loop section for bus no. 5, the journey time saving benefit to bus passengers related to the A355 Route Enhancement scheme are likely to be insignificant;

• The model outputs from Slough SMaRT show that the saving in travel time introduced by the bus priority measures has little impact on induced traffic and modal shift.

• Although it is envisaged that the A355 Route Enhancement scheme will have major impacts on travel time savings, the overall cost changes are likely to be marginal based on the fact that:

a) Slough is a relative compact area and the A355 is a strategic route which attracts a large quality of long distance movements. When applying cost damping function for these movements the overall journey time cost saving is smaller;

b) The 2014 TomTom data shows that the journey time between M4 J6 and A4 Bath Road on A355 is around 3-4 minutes. The overall journey time saving of the scheme is unlikely to exceed 2 to 4 minutes3, which means the modal shift impact is most likely to be insignificant, as described in WebTAG M2 para. 2.3.8.

c) The comparison of initial assignments between A355 Do Minimum and Do Something for the preferred option shows there isn’t substantial network wide rerouting in forecasting year 2017 and 2027, which indicates that impacts of modal shift are likely limited.

The proposed approach 3.26. The key objective of the strategic modelling is to be able to give an accurate forecast of the likely

transport impacts that the proposed A355 Route Enhancement scheme would have on highway users on the A355 and surrounding road network. The scheme will improve journey times and journey time reliability of the highway network, mostly through the increased capacity and improved timings of the Copthorne Roundabout.

3 Based on tests by Atkins for Slough A355 pinch-point funding project undertaken in 2013.



3.27. It is expected that the journey time savings are not sufficiently significant to impact on modal shift. The full variable and WebTAG compliant model built within SMMTM has the following demand response hierarchy (in line with WebTAG): choice of frequency, mode, departure time, destination and sub-mode, ranked in increasing sensitivity.

3.28. The potential impacts of the A355 Route Enhancement will be analysed using the existing SATURN highway models, following a fixed assignment approach. It is assumed that benefit of the scheme to public transport users will be neutral.

3.29. Forecasts for two years, 2017 (the year of scheme opening) and 2027 (ten years thereafter) will be carried out for three time period, i.e. AM, IP and PM. The ‘Do Minimum’ scenario will include all key committed development and (highway and public transport) schemes in Slough that are forecast to be completed by the end of each forecast year, assuming the same as what have applied the existing SMaRT model in year 2015 and 2025.

3.30. For ‘Do Something’ tests, a preferred scheme option, a low cost alternative, and an alternative option will be considered. Forecasts will also be generated for high growth and low growth scenarios to be used in sensitivity tests.

Sensitivity testing 3.31. WebTAG Unit M4 section 4.2 defines how high and low growth scenarios need to be applied to

the central forecast to allow for uncertainty and these will be undertaken for forecasts in year 2017 and 2027 in accordance to the method outlined in WebTAG

3.32. WebTAG Unit M2 paragraph 2.2.6 gives a test to assess the need for variable demand modelling: “Where preliminary calculations using an existing variable demand model are carried out, it will be acceptable in general to use a fixed demand assessment where the resulting difference in suppressed/induced traffic when using the demand model does not change benefits resulting from a scheme by more than 10% in the opening year and 15% in the forecast year (10 to 15 years later) relative to a fixed demand case”. Accordingly, if the highway journey time savings are found to be material, the existing DIADEM can be used as a sensitivity test to capture the impacts of destination choice which are most sensitive to the cost changes as in the existing SMMTM demand model.



4. Appraisal methodology

Economic appraisal 4.1. The economic appraisal will make use of a range of independent assessments. Some of these

will be based upon the transport modelling set out in Section 3 of this document, while others will capture factors external to those being modelled. The proposed methodology considers TAG Units A1 and A2 – Cost Benefit Analysis and Economic Impacts.

Scenario specification 4.2. In order to highlight the value of certain assumptions to the value for money of the scheme as a

whole and to demonstrate the resilience of the scheme to the potential for inaccuracies in future forecasts a range of scenarios will be tested in the model.

Do Minimum scenario

4.3. All Do Something scenarios will be assessed relative to the same Do Minimum Scenario. This includes all existing and committed transport infrastructure and services, with demand levels generated in accordance with the details set out in Section 3 above.

Core scenario

4.4. Similarly to the Do Minimum Scenario, the Core Scenario for the economic case will be based upon the modelled Do Something scenario preferred option which involves the remodelling of the Copthorne roundabout to provide a ‘hamburger’ style roundabout with three lanes to the south of the roundabout continuing south to the M4 including across the Chalvey High Street Bridge.

Sensitivity testing

4.5. Four sensitivity tests will be carried out in the economic assessment of which two will demonstrate the sensitivity of the business case to variations in benefits. These will be in line with the Core Scenario but making use of the high and low growth model outputs.

Scenario 1 – Core Scenario + High Growth

Scenario 2 – Core Scenario + Low Growth

The remaining two sensitivity tests will indicate how resilient the Business Case is to changes in costs. Detailed cost analysis has been carried out for the capital costs, but at this stage no QRA has been carried out, so an element of unknown risk remains. Final costs may therefore be either higher or lower than currently forecast, so a scenario will be presented in which final costs are x% higher or lower than the central forecast, where x will be determined according to the results of the QRA.

Scenario 3 – Core Scenario + x% Capital Cost

Scenario 4 – Core Scenario – x% Capital Cost

Alternative scenarios

4.6. Two alternative scenarios will also be tested in order to consider less costly options and their impacts on user benefits:

Alternative Scenario A – Core Scenario but with only two lanes through the roundabout in each direction and south of the roundabout to the M4, including across Chalvey High Street Bridge. This option requires no bridge works or road widening.

Alternative Scenario B – This is the ’Eton scheme’ which introduces signalisation of three arms of the Copthorne Roundabout, a left slip road from Cippenham Lane and minor engineering works on approaches.



User benefits

Time periods

4.7. Benefits will be calculated through modelling for three hours – an AM peak hour, a PM peak hour and an average inter-peak hour. Based on these modelled time periods, traffic flow data will be used to replicate all-day benefits, so far as is reasonable, through use of representative proportions of the modelled hours. The relationship between user benefits and traffic flows in the modelled periods will be used to determine these factors.

Appraisal period

4.8. The primary element of this scheme is the implementation of the remodelled roundabout and road widening. With adequate maintenance these infrastructure improvements will not be limited to a finite period of operation and costs of renewing assets are included in the appraisal. Therefore the appraisal period will be set at 60 years.

Additional user time savings

4.9. User time benefits will predominantly be captured using a TUBA assessment based upon the highway elements of the transport model.

Revenue 4.10. There is no revenue associated with this scheme.

Limitations of the modelling 4.11. Mode shift is not considered as there is no public transport alternative on the route and journey

time savings of greater than 2 minutes are not expected (see 3.25.).

Scheme costs 4.12. The costs of scheme implementation will be assessed to capture changes to infrastructure.

These costs will include risk (risks determined through a risk workshop with key stakeholders) and be adjusted for real cost inflation and optimism bias as appropriate for a scheme at preliminary design stage. Any additional maintenance or renewal costs which may be required will also be captured.

Accidents

COBALT

4.13. Local accident data will be used to identify current levels of collisions within the study area and this will enable a quantified assessment of the accident reductions forecast as a result of the scheme.

4.14. The impact of the scheme on road traffic accidents will be assessed on a combined link and junction basis using the COBALT software package. This will capture the effects of changing link speeds and flows resulting from the scheme. The ‘hamburger’ junction type is not available in COBALT but will be coded link by link and by available junction types between those links.

Reliability 4.15. The impacts of the scheme on car journey times are expected to show a positive effect resulting

from journey time improvements and decongestion at the main junction. An assessment of journey time reliability will be included.

Regeneration/Wider economic impacts 4.16. The scheme will support local development and have a positive impact on business and non-

business users and transport operators. However, regeneration and wider economic impacts as per webTAG guidance won’t be realised so no assessment will be carried out to capture this.



Distributional Impacts (DIs) 4.17. Social and Distributional Impact (DI) assessments are used to evaluate a transport intervention’s

social impacts and how they vary across the different social groups. The proposed methodology considers TAG Unit A4 – Social and Distributional Impacts.

4.18. DI appraisal will take place as per the 3 stage process outlined below.

4.19. Step 1 is a screening process which identifies the likely impacts for each indicator. The results of this process will be entered into a screening proforma.

4.20. Step 2 is the assessment process which includes:

• Confirmation of the area impacted by the transport intervention (impact area);

• Identification of social groups in the impact area; and

• Identification of amenities in the impact area.

4.21. Step 3 is the appraisal of impacts which completes a full appraisal of the DI and completion of the

Appraisal Summary Table (AST).

4.22. There are eight indicators to be assessed. These have been outlined below including the results of the initial screening:

• User benefits – yes, proceed to step 2

• Noise – to be assessed following modelling results

• Air quality – to be assessed following modelling results

• Accidents – to be assessed following modelling results

• Personal affordability - to be assessed following modelling results

• Security – No impact

• Severance - to be assessed following modelling results

• Accessibility - No impact

Environmental scoping 4.23. Guidance published by the Government for the preparation of Environmental Assessments of

road schemes is contained in the Department of Transport’s Design Manual for Roads and Bridges (DMRB) Volume 11 Environmental Assessment sections 1, 2 and 3 sets out both the general process and the methods for assessing individual environmental topics. The proposed methodology also considers TAG Unit A3 - Environmental Impact Appraisal.

4.24. Prior to the commencement of works on the environmental assessment it is best practice to establish the scope of the environmental assessment (HA 204/08). The objective of this is to identify the environmental topics to be taken into account in respect of the A355 Route Enhancement Scheme and to set out the methodology for assessment. This appraisal will ascertain which environmental topics are to be examined in greater detail i.e. a simple or detailed assessment, and which can be ‘scoped out’ (basic assessment). It should be noted that environmental appraisal inputs into an ASR whilst similar to a scoping stage, is not a formal scoping report in accordance with HA 204/08 although principles of this guidance, in terms of determining potential impacts and appropriate level of subsequent assessments i.e. basic, simple and detailed area adopted for the ASR. For each topic the following sections will be considered:

• Baseline conditions and need for further assessment;

• Significance of effects; and

• Scope for mitigation.



Baseline conditions and need for further assessment 4.25. The baseline conditions for each of the environmental topics covered by the environmental

assessment report will include a review of available information using various methods, including literature research, site surveys/investigations, consultations and desktop review of previous reports and studies. A simplified baseline/existing knowledge and data section is included in this report, which identifies existing conditions and the need to undertake further surveys required to provide a more accurate baseline of existing conditions. This will provide a more robust prediction of the environmental impacts of the A355 Route Enhancement scheme.

Significance of effects 4.26. The assessment will identify the potential impacts that might occur due to the construction and

operation of the A355 Route Enhancement scheme. Impacts may be adverse/negative or beneficial/positive, direct, indirect, secondary or cumulative, temporary or permanent, short, medium or long term. Impacts can affect the environment in a variety of ways. The differing parts of the environment affected by a scheme are known as receptors, i.e. those things that receive an impact from a scheme. Receptors can range from individual plants, animals or human beings living in or passing through the area, through to the landscape as a whole and the physical, ecological and cultural elements within it.

4.27. The assessment of the impacts of the A355 Route Enhancement scheme will be based on agreed mitigation measures being designed into the scheme, taking account any change in effectiveness over time, such as growth of planting, the establishment of new habitats or the change in noise generation from older road surfaces.

4.28. Chapter of DMRB Volume 11 Section 2 Part 5 introduces the general principle underlying the assessment process, which can be summarised generally, although not necessarily for every topic, as a three-step process:

• The evaluation of the value, importance or sensitivity of the receptors;

• Assessment of the magnitude of the impact of the scheme on the receptor, be it adverse or beneficial; and

• Determination of the significance of the effect resulting from combining the impact (of a certain magnitude) on a receptor (of a particular value).

Significance criteria will be set out for each assessment topic following this three step approach. See the following assessment matrix, to determine value of sensitivity of receptor, the magnitude of impact to determine the significance of effect.

Figure 4.1 Assessment matrix4

Magnitude of Impact (Degree of Change)

En

vir

on

men

tal

Valu

e

(Sen

sit

ivit

y)

No Change Negligible Minor Moderate Major

Very

Hig

h

Neutral Slight Moderate or

Large Large or

Very Large Very Large

Hig

h

Neutral Slight Slight or Moderate

Moderate or Large

Large or Very Large

4 Source: DMRB Volume 11 Section 2 Part 5



Mediu

m

Neutral Neutral or

Slight Slight Moderate

Moderate or Large

Low

Neutral Neutral or

Slight Neutral or

Slight Slight

Slight or Moderate

Neglig

ible

Neutral Neutral Neutral or

Slight Neutral or

Slight Slight

Scope for mitigation 4.29. The following list summarises the basic principles which road design should seek to adhere to:

• Biodiversity: avoid key sites; help create new habitats through careful use of trees, hedgerows and ground cover;

• Land use: avoid high grade agricultural land, where possible;

• Noise: use design to avoid noise at sensitive locations, e.g. careful choice of horizontal and vertical alignment; use of low noise surfaces. If problems persist, consider the use of noise fences or bunds, and as a last resort use double glazing to cut down noise levels inside dwellings;

• Water and flooding: in order to avoid rapid discharge of rainwater into watercourses, the use of balancing ponds is proposed. This and other forms of sustainable urban drainage systems (SUDS) could benefit water quality, and in turn foster improvements to biodiversity quality;

• Landscape: use of planting and topography to ‘hide’ development from public view; and

• Pedestrians, cyclists, equestrians and community effects: use design to ensure that the local network fosters walking, horse-riding and cycling.

Environmental topics 4.30. The following topics are considered according to the criteria outlined above:

• Noise;

• Air quality;

• Greenhouse gases;

• Landscape and townscape;

• Heritage and historic resource;

• Ecology and nature conservation; and

• Water environment.

Noise 4.31. The assessment and mitigation of road traffic noise and vibration is carried out according to

established prediction and assessment methodologies that are governed or guided by the following key documents:

• DMRB Volume 11, Section 3, Part 7 – Noise and Vibration 2011 HD213/11 Revision 1, which includes guidance on the assessment methods for noise and vibration from new highways;

• The Calculation of Road Traffic Noise 1998 (CRTN);



• Noise Insulation Regulations 1975 (as amended);

• The Highways Noise Payments and Movable Homes (England) Regulations 2000 (as amended); and

• Environmental Protection Act 1990.

Assessment of construction noise and vibration is also carried out according to assessment methodologies that are governed or guided by the following key documents:

• BS 5228 Noise and Vibration Control on Construction and Open Sites 2009; and

• Control of Pollution Act 1974.

Baseline

4.32. The main receptors, in the vicinity of the proposed A355 Route Enhancement scheme, are residential receptors located in proximity to the A355 Tuns Lane. Based on desk based observations of the area surrounding the proposed scheme, the predominant noise source affecting existing noise sensitive receivers is likely to be the A355 Tuns Lane.

4.33. In addition, the A355 Tuns Lane sits within a First Priority Location (this can be viewed within the Department for Environment, Food and Rural Affairs (DEFRA) Noise Action Plan, Major Roads Map number 129).

Methodology

4.34. The objective of an assessment at this basic (scoping) is to establish an appreciation of the likely noise and vibration consequences associated with the project. DMRB Volume 11, Section 3, Part 7 – Noise and Vibration 2011 HD213/11 Revision 1 provides threshold values against which changes in noise due to the project should be compared, and assessed in both the short-term (on scheme opening) and in the long-term (over the design period, typically 15 years after scheme opening).

4.35. The threshold criteria for traffic noise assessment during the day time period is a permanent change in magnitude of at least 1dB(A) LA10, 18hr in the short-term, or of at least 3dB(A) LA10,18hr in the long-term. Additionally, for night-time noise impacts, a threshold criterion of a change in magnitude of at least 3dB(A) Lnight, outside applies, but only where an Lnight, outside greater than 55dB is predicted in any scenario.

4.36. The first step in assessing if an assessment should continue beyond scoping (basic assessment) stage is to identify if the A355 Route Enhancement scheme will result in any physical changes to the vertical or horizontal alignment of carriageway; if there will be any changes in traffic flow, composition or speed; or if there will be any other changes to infrastructure with the potential to result in changes to noise levels in the vicinity.

4.37. The second step in assessing if an assessment should continue beyond scoping (basic assessment) stage is to identify the extent of the study area and establish if any noise sensitive receptors (dwellings, hospitals, schools, community facilities, or designated areas such as AONB, SAC, SPA, SSSI etc.) exist within the study area.

The DMRB requires calculations of noise impacts at locations within 600m of both a scheme boundary, and within 600m of any other affected routes within 1km of a scheme boundary – this area is referred to as the detailed calculation area. For affected routes outside of this area where noise calculations have been undertaken, the study area is defined as 50m either side of the centreline of these routes. A route is affected where a change in noise of more than 1 dB(A) on opening or of more than 3 dB(A) over the design period is predicted – these routes are referred to as the wider road network, and form the wider calculation area. DMRB notes that if any sensitive receptors are identified within the study area then the assessment must continue to at least a simple stage assessment, depending on the expected potential for noise and vibration impacts.

4.38. The final step in assessing if an assessment should continue beyond scoping (basic assessment) stage is to identify if the threshold values are likely to be met or exceeded. If it is clearly evident that the threshold values will be exceeded then assessment should progress to a detailed stage assessment.



Likely scale of impact

4.39. The A355 Route Enhancement scheme may increase the number of car vehicle journeys due to currently supressed demand being realised but will also reduce congestion.

4.40. In the absence of robust forecast traffic data corresponding to the scheme it is anticipated that the operational phase of the proposed scheme would result in a number of changes to noise sources due to alteration of the alignment of the running lanes and differences in the flow, speed and composition of traffic which could impact upon receptors in proximity to the A355 Tuns Lane. DMRB requires that traffic flow data be provided as 18-hour annual average weekday traffic flows (AAWT). For an increase in noise level of 1dB LA10,18-hour, the predicted change in traffic flow would have to increase by 25% or decrease by 20%, while a 3dB LA10,18-hour change would correspond to an increase in traffic of at least 100% or a decrease of at least 50%. This results in a need for a detailed noise assessment to be undertaken as set out below.

4.41. Existing traffic data will be used to predict the change in noise level on the road links represented by the traffic model. The basic noise level expected to be experienced will be calculated in accordance with the methodology as set out in the Department for Transport document ‘Calculation of Road Traffic Noise 1988’ (CRTN). The difference between the basic noise levels for differing scenarios may then be compared to present the expected noise impacts of the A355 Route Enhancement scheme.

4.42. Typically the short-term (opening) impact of such a scheme would be presented by comparing the opening year Do something against the opening year Do minimum; and the long-term impact would be presented by comparing the future year Do something against the opening year Do minimum.

4.43. It is anticipated that construction of the A355 Route Enhancement scheme could potentially cause noise and vibration disturbance to receptors proximate to the scheme, for example through construction traffic travelling to and from worksites, ground breaking, aggregate handling etc. associated with widening works. Such impacts, however, would be limited by the use of best practicable means, which would be set out in a Construction Environmental Management Plan.

Summary

4.44. It is considered that the A355 Route Enhancement scheme would result in a number of changes to noise sources which could impact upon receptors in proximity to the A355 Tuns Lane. As a consequence a further, more detailed, assessment in accordance with the DMRB will be undertaken.

Air quality

Existing knowledge and data

4.45. The air quality study area is currently defined as within 200m of the A355 Route Enhancement scheme corridor (i.e. within 200m of the A355 between the A4 and M4 junction 5) as traffic data in a suitable format was not available at this time to determine changes in traffic, composition and speed due to the A355 Route Enhancement scheme to enable an air quality affected road network to be identified.

4.46. The air quality study area is within the boundaries of Slough Borough Council and also within Air Quality Management Area (AQMA) number 3. Slough Borough Council carry out regular reviews and assessments of local air quality and these will be considered.


4.47. The A355 Route Enhancement scheme may increase the number of vehicles using the A355 Tuns Lane. The need for air quality assessment is determined in accordance with traffic change criteria set out in HA207/07 DMRB Volume 11 Section 3 Part 1, based on comparing without scheme (Do Minimum) and with scheme (Do Something) scenarios in the opening year. The traffic change criteria are:

• road alignment will change by 5m or more, or



• daily traffic flows will change by 1,000 annual average daily traffic (AADT) or more, or

• HDV flows will change by 200 AADT or more, or

• daily average speed will change by 10 km/hr or more, or

• peak hour speed will change by 20 km/hr or more.

4.48. The possible increase in road traffic is not expected to exceed the air quality traffic change criteria for HDV flows however this cannot be confirmed at this stage.

4.49. Given the possible changes in traffic due to the A355 Route Enhancement scheme, the absence of robust forecast traffic data corresponding to the scheme and the location of air quality sensitive receptors relative to road widening the effect on air quality at this stage cannot be confirmed until further assessment using forecast traffic data is undertaken.

Data requirements and survey approach

4.50. Any further air quality assessment would require road traffic flow data for a base year, and without and with the scheme in the opening year. Data for future year traffic scenarios should account for traffic associated with all committed developments in the local authority area and should apply appropriate growth factors. The following data are the minimum required for each road link where traffic is expected to change as a result of the A355 Route Enhancement scheme in each scenario:

• 24-hour annual average daily traffic (AADT) flow (combined for 2-way roads);

• Percentage heavy duty vehicles (HDVs). An HDV is any vehicle with a gross weight in excess of 3.5t, including heavy goods vehicles and coaches;

• Average daily speed for each road link in km/hour traffic model data for flow, composition and speed.

4.51. Ongoing air quality monitoring surveys are being undertaken by Slough Borough Council. No additional air quality surveys are proposed.

Proposed methodology

4.52. Any further air quality assessment will be undertaken principally following the guidance given in DMRB HA207/07. The assessment would focus on operational effects for local air quality. This will be reported in the Business Case.

Summary of communications

4.53. Air quality consultation with the air quality specialist at Slough Borough Council will be undertaken.

Summary of risks

4.54. The primary risk for the air quality assessment is related to the use of the transport model outputs. Table 4-1 summarises the risks.

Table 4-1 Risks for air quality


Severity (H/M/L)

Mitigation RR

AQ1

A change in the traffic forecasts during the scheme development which results in a change to the air quality assessment affected road network.

Medium High

− Determine the traffic model reliability area and the air quality assessment affected road network (ARN) at the earliest possible opportunity after traffic model forecasts are complete at each stage in the scheme development.

− Close communication between traffic forecasting team and air quality specialists throughout the scheme development.

Medium



Greenhouse gases

Existing knowledge and data

4.55. Baseline greenhouse gas emissions data specifically for the scheme are is not currently available.

Constraints

4.56. There are not expected to be constraints related to greenhouse gases.


4.57. The greenhouse gases assessment is concerned with changes in emissions of carbon dioxide (CO2). The A355 Route Enhancement scheme may increase the number of vehicles using the A355 and may alter the average speed of vehicles (increasing where congestion currently exists, reducing it if over 30mph in any locations due to new speed limit).

4.58. The need for assessment is determined in accordance with traffic change criteria set out in HA207/07 DMRB Volume 11 Section 3 Part 1, based on comparing without Scheme (Do Minimum) and with Scheme (Do Something) scenarios in the opening year. The traffic change criteria are:

• road alignment will change by 5m or more, or

• daily traffic flows will change by 1,000 annual average daily traffic (AADT) or more, or

• HDV flows will change by 200 AADT or more, or

• daily average speed will change by 10 km/hr or more, or

• peak hour speed will change by 20 km/hr or more.

4.59. The possible increase in road traffic is not expected to exceed the traffic change criteria for HDV flows and on this basis the changes in greenhouse gas emissions are expected to be scoped out once robust forecast traffic data corresponding to the A355 Route Enhancement scheme is available.

Data requirements and survey approach

4.60. Any further air quality assessment would require road traffic flow data for a base year, and without and with the scheme in the opening year. Data for future year traffic scenarios should account for traffic associated with all committed developments in the local authority area and should apply appropriate growth factors. The following data are the minimum required for each road link where traffic is expected to change as a result of the A355 Route Enhancement scheme in each scenario:

• 24-hour annual average daily traffic (AADT) flow (combined for 2-way roads);

• Percentage heavy duty vehicles (HDVs). An HDV is any vehicle with a gross weight in excess of 3.5t, including heavy goods vehicles and coaches;

• Average daily speed for each road link in km/hour traffic model data for flow, composition and speed.

4.61. No surveys are proposed for greenhouse gases.

Proposed methodology

4.62. Any further greenhouse assessment will be undertaken principally following the guidance given in DMRB HA207/07. The assessment would focus on operational effects for greenhouse gases and would be reported in the Business Case.

Summary of communications

4.63. No consultation is proposed for greenhouse gases.



Summary of risks

4.64. The primary risk for the greenhouse gas assessment is related to the use of the transport model outputs. Table 4-2 summarises the risks.

Table 4-2 Risks for greenhouse gases


Severity (H/M/L)

Mitigation RR

GHG1

A change in the traffic forecasts during the scheme development which results in a change to the air quality assessment affected road network.

Medium High

Determine the traffic model reliability area and the air quality assessment affected road network (ARN) at the earliest possible opportunity after traffic model forecasts are complete at each stage in the scheme development.

Medium

Landscape and townscape

Baseline

4.65. The Countryside Character Initiative, overseen by Natural England, is concerned with the character of England’s countryside at the end of the 20th Century and has mapped the country into 159 separate, distinctive character areas. These National Character Areas (NCA) are intended to contribute towards policy development and local planning, action and development. The proposed A355 Route Enhancement scheme lies within National Character Area (NCA) 115 Thames Valley. The key characteristics relevant to the study area are:

• The Thames Valley is a mainly low-lying, wedge-shaped area, widening from Reading, which includes Slough, Windsor, the Colne Valley and the southwest London fringes.

• The River Thames provides a unifying feature through a very diverse landscape of urban and suburban settlements, infrastructure networks, fragmented agricultural land, historic parks, commons, woodland, reservoirs and extensive minerals workings.

• Hydrological features dominate the Thames Valley, and include the Thames and its tributaries, part of the Grand Union Canal and the reservoirs which form the South- West London Waterbodies Special Protection Area (SPA) and Ramsar site. As well as the Thames and its tributaries, around Slough, the Colne Valley and areas further east, the overwhelming influences are from lakes left from mineral workings and vast raised reservoirs.

• In the south-west, the gently rolling valley sides give way to a flatter plain east of Reading, which widens to include the Slough and Windsor areas. Much of this area is near flood level, although Slough lies on slightly terraced land above the flood plain and Windsor Castle sits on a prominent local outcrop of chalk.

• The Thames Valley NCA is dissected by major transport links that connect London to the west, including the M4, M40, the London orbital (M25), and the Paddington main line to the west, as well as a plethora of A-roads linking the main urban areas.

4.66. The proposed A355 Route Enhancement scheme location has no statutory landscape designation in the study area.

Methodology

4.67. The methodology for the assessment will involve undertaking a desk based scoping study including an assessment of properties and local views potentially affected by the A355 Route Enhancement scheme.

4.68. If the scoping determines a need for further assessment, this will be based on DMRB IAN 135/10 Landscape and Visual Effects Assessment that aligns the landscape, townscape and visual assessments with the generic guidance provided in IAN 81/06. The DMRB approach requires an appreciation of the landscape context, as a basis to evaluate the sensitivity of the surroundings to visual change and the constraints placed upon the design of the highway scheme and its



environmental measures. Work includes identification of landscape character areas and detailed assessment of the visual impact of the proposals on public visual receptors including residential property, public rights of way and public open space in the area. This analysis is carried out concurrently with the scheme design and forms part of a continuing process of design refinement, ensuring that the landscape proposals are developed as an integral part of the project.

4.69. The Countryside Agency (now part of Natural England) produced detailed guidance on the systematic identification and evaluation of landscape character, of which the current edition was published in April 2002. This includes the idea of a sequential depiction of the landscape character, from regional down to local level, with the level of detail amended to suit the scale of the study.


4.70. Whilst the majority of the A355 Route Enhancement scheme’s proposals are alterations to the existing road environment, the scheme could have adverse effects, including:

• Loss of habitat through loss of young lime trees on the Copthorne roundabout;

• Loss of habitat through loss of flower beds on Copthorne roundabout and centre of A355 Tuns Lane;

• Impact on visual amenity by tree and flower bed removal on A355 Tuns Lane; and

• Impact from the new layouts, associated signage and highways design on visual amenity.

Summary

4.71. Further consideration of the potential loss of 9 trees is needed and an environmental appraisal will inform the design process and assist in formulating the detailed design proposals. It is therefore proposed that simple assessment should be used due to the potential significant landscape and visual effect that is anticipated through tree removal.

Heritage of historic resources

Baseline

4.72. Due to being heavily bombed during World War II, Slough’s heritage and historic resources tend to be scattered on the outskirts of the town; however Slough has 96 listed buildings remaining. Within the scheme corridor there are no historic resources.

Methodology

4.73. The historic environment resource encompasses designated and undesignated assets including Scheduled Monuments, Listed Buildings (statutorily listed and locally listed), Conservation Areas, World Heritage Sites, Registered Parks and Gardens, Registered Historic Battlefields, historic buildings (unlisted), known archaeological sites and areas of archaeological potential. The methodology for the assessment will involve undertaking a desk based scoping study considering the character and quality of the study area.

4.74. If the scoping study deems in necessary an assessment will be undertaken as part of the environmental assessment for the three sub-topics as identified in DMRB as follows:

• Archaeology: the potential effects on known and as-yet unknown archaeological remains;

• Built heritage: potential physical impact on designated and un-designated built heritage assets and changes to the setting of designated heritage assets in the landscape (including long views); and

• Historic landscape character: potential visual alterations of the integrity of the historic landscape character within which the proposal site is situated.

4.75. If the full assessment is required, baseline information would be collected from a number of sources, including (but not limited to):

• Berkshire Historic Environment Record (HER);



• National Heritage List for England maintained by English Heritage;

• Cartographic (including superseded Ordnance Survey maps and other relevant historic mapping);

• Aerial photographic data held by Slough Borough Council (if available);

• Historic Landscape Characterisation data; and

• Relevant secondary sources to inform the archaeological and historic background of the assessment.

4.76. In addition following the initial data collection, a walkover survey would be carried out in relation to relevant scheme elements as part of the environmental assessment process, with the aim to identify known constraints and their condition, to assess the potential for survival of constraints as yet unidentified (i.e. buried archaeological remains), and to assess the setting and sensitivity of any visual receptors identified.

4.77. Slough Borough Council’s Historic Environment Service and Conservation Officer (or equivalent) will be consulted further on any issues identified and the need for further field-based assessment and/or mitigation in relation to them.

4.78. Within the environmental assessment process, the significance of effect would be determined through assessing the magnitude of predicted change and the importance of the affected resource. The scale of impact of the proposed scheme on the heritage resource will be described qualitatively in the assessment, in terms of impairment or loss of significance. Incremental, secondary or cumulative impacts will be considered. This methodology is based on that set out in the DMRB Volume 11, Section 3, Part 2, Cultural Heritage, paragraphs 5.13.1 (Archaeological Remains); 6.13.1 (Historic Buildings); 7.13.1 (Historic Landscapes). This is the standard methodology used for quantifying impacts on the historic environment resource.

4.79. The value (or significance) of each element of the historic environment resource would be determined using methodologies broadly reflecting the Secretary of State’s criteria for Scheduling Monuments. The value of the built heritage would also take into consideration whether features or sites are statutorily designated or not.

4.80. By combining the magnitude of the impact (or change) as a result of the A355 Route Enhancement scheme and the significance of each resource, and based on professional judgement, an assessment will be made of the significance of effect, taking into account the possibility and nature of mitigation.


4.81. The types of impacts that can occur include physical impacts such as destruction or truncation of assets, and setting impacts, which occur when a new structure impacts negatively on the surroundings in which a heritage asset is experienced. Both of these types of impact can diminish the significance of heritage assets.

4.82. There should be no physical impacts to above ground heritage assets, such as Listed Buildings, arising from the A355 Route Enhancement scheme. Ground works associated with the proposed widening of the A355 Tuns Lane and changes to Copthorne roundabout would have the potential to truncate or destroy any as yet unknown archaeological remains buried within the scheme’s land take however this is very unlikely due to the extent of the scheme.

Summary

4.83. In light of the limited extent of the scheme, any such anticipated impact is anticipated to be minor; so in that regard further historic assessment should be scoped out.



Ecology and nature conservation

Baseline

4.84. There are no Wetlands of International Importance (Ramsar), Special Protection Areas (SPA), Special Area of Conservation (SAC), Sites of Special Scientific Interest (SSSI) within 2 km of the proposed works.

Methodology

4.85. Due to the small scale and localised nature of the A355 Route Enhancement scheme it is not considered that the impacts would extend beyond the footprint of the road construction and its immediate surroundings. Therefore a maximum zone of 2km is appropriate for the search area for statutory designated sites and 1km is appropriate for the desk study search area for non-statutory sites and notable and protected species. The scoping study will consider the nature of the scheme and decide on an appropriate area to survey (this will consider the scheme footprint itself - the road plus construction area, access routes and storage areas – plus a given distance around this).

4.86. The assessment and characterisation of impacts for the purposes of an environmental assessment, if required according to the scoping study, would be carried out following the approach set out in DMRB Volume 11, Section 2 Part 5 and IAN 130/10. As set out in section 2.5 of the IAN, the valuation of receptors and characterisation of ecological impacts would be considered to in order to determine the significance of impacts of the proposed works.

4.87. The nature conservation value or potential value of an ecological feature (or receptor) is determined within a defined geographic context:

• International importance (e.g. Special Areas of Conservation, Special Protection Areas, Ramsar sites);

• National importance (e.g. Sites of Special Scientific Interest in England, Scotland and Wales and Areas of Special Scientific Interest in N Ireland);

• County importance (e.g. Sites of Importance for Nature Conservation);

• Important within the District/ Borough;

• Local (parish) importance (e.g. significant ecological features such as old hedges, woodlands, ponds);

• Important within the site and immediate environs e.g. habitat mosaic of grassland and scrub (i.e. within the zone of influence only); and

• Negligible importance would usually be applied to areas such as built development or areas of intensive agricultural land.

4.88. It should be noted that it is usual to consider habitats and species together when ascribing a value to a feature using this geographic context. However, there are circumstances where an ecologist may feel it necessary to assign a value to a particularly valuable species. In assigning value to species it is necessary to consider the species distribution and status including a consideration of trends based on available historical records and to make use of any relevant published evaluation criteria. For instance, the presence of a significant population of European protected species such as bats may be worth separate consideration.

4.89. If required as per the scoping study an assessment of the potential impacts of the A355 Route Enhancement scheme would need to take into account both on-site impacts and those that may occur to adjacent and more distant ecological features. Impacts can be positive or negative. Negative impacts can include:

• Direct loss of wildlife habitats;

• Fragmentation and isolation of habitats;

• Disturbance to species from noise, light or other visual stimuli;

• Changes to key habitat features; and



• Changes to the local hydrology, water quality and/or air quality.

4.90. Negative and positive impacts on nature conservation features have been characterised based on predicted changes as a result of the proposed activities. In order to characterise the impacts on each feature, the following parameters are taken account of:

• The magnitude of the impact;

• The spatial extent over which the impact would occur;

• The temporal duration of the impact;

• Whether the impact is reversible and over what timeframe; and

• The timing and frequency of the impact.

4.91. The assessment would identify those positive and negative impacts which would be ‘significant’, based on the integrity and the conservation status of the ecological feature. Impacts are unlikely to be significant where features of local value or sensitivity are subject to small scale or short-term impacts. However, where there are a number of small scale impacts that are not significant alone, it may be that, cumulatively, these may result in an overall significant impact.

4.92. Assessment would consider ecological mitigation that would then be incorporated into the detailed design of the A355 Route Enhancement scheme and the programme and methods for site works, particularly any works involving vegetation clearance. Mitigation will be designed to take account of legal requirements regarding protected species as well as any significant impacts indicated by the environmental assessment.


4.93. The likely impacts during construction and operational phases are listed in Table 4-3.

Table 4-3 Likely ecology impacts of the scheme in construction and operation

Ecological Feature Description of likely construction and operational impact

Trees

Construction: The number of trees to be affected by the proposed works can only be confirmed following a landscape/arboricultural survey and once the final design is confirmed but is likely to be 9 with 3 trees to be felled and 6 relocated.

Operation: There could be impacts on remaining non-felled trees and relocated trees (i.e. to their root zones) adjacent to A355 Tuns Lane. Mitigation will need to be advised by an arboriculturalist.

Hedges

Construction: Potential for severance and loss of hedgerow and associated ground flora would be confirmed upon ecology survey if deemed necessary.

Operation: No impact on hedgerows is anticipated during the operation of the A355 Route Enhancement scheme. New hedges could be planted to mitigate for lost hedgerow to ensure there is no net loss of this habitat if any is required.

Bats

Construction: Potential loss of habitat in trees and fragmentation of tree line canopy and hedge lines features which may be used as commuting routes.

Operation: No impacts are anticipated during the operation of the scheme following implementation of mitigation advised as a result of ecology survey.

Birds

Construction: Potential loss of breeding bird habitat in the form of hedges, scrub, shrubs and trees.


Reptiles

Construction: Potential loss of habitat; hedgerows, grass verges and scrub used as basking, foraging and shelter sites.




Amphibians

(great crested newts)

Construction: Potential loss of terrestrial habitat; hedgerows, grass verges and scrub used as basking, foraging and shelter sites.


Summary

4.94. Whilst the majority of works proposed are within the existing road boundary and much of the work is relatively superficial, at this stage construction sites are not known and along with vegetation removal for widening there could be minor loss of habitat. Furthermore, the loss and relocation of trees could lead to adverse effects on species such as bats and birds. The key adverse impacts are therefore:

• The permanent loss and/or fragmentation of habitats (trees and potentially hedges);

• The potential loss of bat roosts;

• The potential fragmentation of bat flight lines and potential loss of foraging habitat;

• The loss of breeding bird habitats; and

• The potential loss of habitat suitable for reptiles.

4.95. The scoping study will consider the potential for protected species/nesting birds to be present in trees proposed for felling and may therefore recommend a further simple assessment due to the potential presence of protected species, if so this would be undertaken.

Water environment

Baseline

4.96. Whilst the majority of the scheme is an urban environment, several drains either bisect or are adjacent to the proposed A355 Route Enhancement scheme’s route.

Methodology

4.97. At the scoping stage, identification of likely significance of effects is qualitative and follows the requirements of the DMRB process as set out in the DMRB HD45/09. The study area for the water environment is defined as 1km from the centre line of the scheme and includes all water bodies, watercourses and associated assets (abstraction points, discharges etc.).

4.98. The likely impacts of the A355 Route Enhancement scheme will be considered in the scoping study and used to answer a set of questions written into the DMRB HD45/09. If any of the answers to the following questions is ‘yes’ then further simple assessment may need to be undertaken:

• Will the scheme affect an existing watercourse or floodplain?

• Will the scheme change either the road drainage or natural land drainage catchments?

• Will the scheme lead to an increase in traffic flow of more than 20%?

• Will the scheme change the number or type of junctions?

• Is any of the scheme located within an indicative floodplain or a Source Protection Zone (SPZ)?

• Will earthworks result in sediment being carried to watercourses?

• Will the scheme allow drainage discharges to the ground?

4.99. This assessment should also include consideration of whether there is to be any culverting (or extensions to culverting), river re-alignment or impact on aquatic ecology to meet any requirements for Water Framework Directive (WFD) 2000/60/EC compliance assessments that may be requested by the Environment Agency.




4.100. Potential impacts from the A355 Route Enhancement scheme during construction include transfer of silt, spillages, working in floodplains, storage of materials and temporary impermeable areas at site compounds.

4.101. The proposed drainage is likely to be kerbs and gullies with some retention built in with oversize carrier pipes. Drainage during operation has the potential to impact on water quality due to increased traffic flows and the increased potential this has on pollutant loading from road runoff. By extending hard surface area of the carriageway, increased volumes of water are collected that can exacerbate flooding.

Summary

4.102. The scoping study will assess the main water receptor. If required further assessment will be undertaken to determine if there will be an adverse impact on the surface or groundwater receptors.



5. Appraisal Specification Summary Table

Impacts Sub-impacts Estimated Impact in OAR

Level of uncertainty in OAR

Proposed proportionate appraisal methodology

Reference to evidence and rationale in support of proposed methodology

Type of Assessment Output (Quantitative/ Qualitative/ Monetary/ Distributional)

Ec

on

om

y

Business users & transport providers

Slight positive Low TUBA analysis based on highway assignment model results

WebTAG guidance and past experience based on size and scope of project

Quantitative / Monetary

Reliability impact on Business users

Slight positive Low Reliability assessment based Journey Time reliability analysis using the highway model

WebTAG guidance and past experience


Regeneration Neutral Low N/A WebTAG definition of 'Regeneration' N/A

Wider Impacts Neutral Low N/A WebTAG definition of 'Wider Impacts' N/A

En

vir

on

me

nta

l

Noise Assumed neutral Medium Scoping study using flows from highway model to assess impacts based on determined thresholds



Air Quality Assumed neutral Medium Scoping study using flows from highway model to assess impacts based on determined thresholds



Greenhouse gases Slight/strong positive

Medium TUBA analysis based on highway assignment model results



Landscape Assumed neutral Low Scoping study WebTAG guidance and past experience based on size and scope of project

Qualitative

Townscape Assumed neutral Low Scoping study WebTAG guidance and past experience based on size and scope of project

Qualitative

Heritage of Historic resources

Assumed neutral Low Scoping study WebTAG guidance and past experience based on size and scope of project

Qualitative

Biodiversity Assumed neutral Low Scoping study WebTAG guidance and past experience based on size and scope of project

Qualitative

Water Environment Assumed neutral Low Scoping study WebTAG guidance and past experience based on size and scope of project

Qualitative



Impacts Sub-impacts Estimated Impact in OAR

Level of uncertainty in OAR

Proposed proportionate appraisal methodology

Reference to evidence and rationale in support of proposed methodology

Type of Assessment Output (Quantitative/ Qualitative/ Monetary/ Distributional)

So

cia

l

Commuting and Other users

Slight positive Low TUBA analysis based on highway assignment model results



Reliability impact on Commuting and Other users

Slight positive Low Reliability assessment based Journey Time reliability analysis using the highway model



Physical activity Assumed neutral Medium N/A WebTAG guidance and past experience based on size and scope of project

Qualitative

Journey quality Slight positive Medium Scoping study WebTAG guidance and past experience based on size and scope of project

Qualitative

Accidents Assumed neutral Medium COBALT analysis based on highway assignment model results and accident statistics



Security Assumed neutral Low Scoping study WebTAG guidance and past experience based on size and scope of project

Qualitative

Access to services Slight positive Low Scoping study WebTAG guidance and past experience based on size and scope of project

Qualitative

Affordability Assumed neutral Medium Scoping study WebTAG guidance and past experience based on size and scope of project

Qualitative

Severance Assumed neutral Medium Scoping study WebTAG guidance and past experience based on size and scope of project

Qualitative

Option values Assumed neutral Low N/A WebTAG guidance and past experience based on size and scope of project

N/A

Pu

bli

c

Ac

co

un

ts Cost to Broad

Transport Budget Moderate negative

Low TUBA analysis based on highway assignment model results



Indirect Tax Revenues

Slight negative Medium TUBA analysis based on highway assignment model results




Appendix



Appendix A. Scheme drawing

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[email protected] +44 (0)20 7121 2265

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