typical peak design hour characteristics

24th ARRB Conference – Building on 50 years of road and transport research, Melbourne, Australia 2010

© ARRB Group Ltd and Authors 2010 1

TYPICAL PEAK DESIGN HOUR CHARACTERISTICS

David K Wanty, MWH New Zealand Ltd, New Zealand.

ABSTRACT This paper fills a knowledge gap in helping practitioners determine what is the appropriate design year traffic flow for current and future planning.

Analysis of continuous classified traffic data is undertaken with the 10th, 30th, etc hourly flow derived as a %AADT for typical urban arterial, peri-urban, rural strategic and rural recreational (winter & summer) highways, and the associated %HV and directional split.

The paper outlines the background and methodology, provides example graphs and analysis tables, discusses the results and summarises the key findings.

Recommendations are provided for adoption by the NZ Transport Agency (NZTA) in particular and suggestions for further improvement in information management and dissemination of the study results for use by practitioners.

BACKGROUND Two years before starting this project, a precursory examination of New Zealand, Australian, and North American guides indicated few firm guidelines on the appropriate design hour to choose as a percentage of the AADT for rural sites. Re-examination has revealed the following

New Zealand (NZ) The NZTA Planning Policy Manual (PPM version 1, effective from 1 August 2007) states in section 3.4.3.2 (repeated in Appendix 6) that in relation to new state highways:

The capacity of new sections of state highway will take into account factors including:

• safety

• projected demand

• the expected outcomes of travel demand management initiatives

• the state highway category

• cost effectiveness and affordability

• Transit’s Draft State Highway Geometric Design Manual (which suggests a design capacity that achieves level of service C in 25 years).

There is no mention of the design hour to use nor of the percentage of AADT to use for computing the design hour flow. The design year to choose is even uncertain, varying it would seem from 10 to 25-30 years. Reference is made in the PPM to “Transit’s Passing and Overtaking Guidelines”, the July 2008 version of which is available again on the NZTA website. Seemingly in response to comments from the author made in 2007, the Transit NZ / NZTA guidelines changed to include the following (refer G1. Planning, Design Hour Flows sub-section):

For passing treatments, assume a 125th design hour at 25 years from construction date. For estimating the percentage growth, refer to the PO web page for projected 2006 and 2031 AADTs [these were updated by the author for NZTA National Office in 2009].

In the absence of any traffic flow data, for rural strategic state highways, assume a 55/45% direction split with a peak flow of 10.5% AADT. This flow should not be exceeded for 95% of hours during the design year [5% of 8760 hours = 439!].

For recreational routes, refer to the EEM Table A7.2 Traffic Flow Profiles for percentage of hourly flow relative to AADT for routes with both low and high volumes of recreational traffic.



Table A7.2 of the NZTA Economic Evaluation Manual Volume 1 (January 2010) gives the hourly flow as a %AADT for two types of (rural) roads, namely those with either low or high volumes of recreational traffic. Generally an hourly flow interval equivalent to 3.5 %AADT has been used but it is uncertain whether the hourly flow is the mid-point or lower limit. Assuming the latter it would appear that for rural highways with low volumes of recreational traffic a 107th design hour relates to 14 %AADT and 10th design hour to 17.5 %AADT, while for rural highways with high volumes of recreational traffic a 164th design hour relates to 17 %AADT, 44th design hour to 17.5 %AADT, and 38th design hour to 25.0 (or 24.5%?) %AADT. These values are used in the default procedure to evaluate the typical benefits of a passing lane on a rural two-way NZ highway1.

Appendix B of the NZTA draft SHGDM (December 2000 with April 2003 amendment) states:

4 TRAFFIC DATA

Include both AADT's and design (peak period) hourly volumes. For rehabilitation projects, use current year traffic. For all others, use design year traffic, usually 25 years after construction is complete. For interim projects that are to be superseded by programmed future construction, provide traffic data for both the ultimate programmed construction year and the ultimate project's design year

Section 2.1.2 of the SHGDM states:

Capacity analysis is described in the Austroads Guide to Traffic Engineering Practice - Part 2: Roadway Capacity and the Highway Capacity Manual (TRB 1985). Design traffic volumes are estimated for a future year, usually 25 years ahead, and the road designed to carry this demand at a predetermined level of service, usually C.

The SHGDM Appendix A checklist also refers to the Level of Service and Design Period / Year, with a default of 25 years inferred unless approved otherwise.

United States (US) The aforementioned Austroads Guide was based largely on the TRB 1985 Highway Capacity Manual (HCM), and both have since been superceded. Chapter 20 of the HCM 2000 (used in the US and Canada) relates the level of service of a rural highway to the design hour flow, the directional split, the percentage of heavy (and slow) vehicles, the percentage of time-spent-following, average travel speed and geometric factors including the carriageway width, and grade (and terrain).

HCM 2000 Exhibit 8-8 shows the ranked hourly volumes (highest 1100 hours) for two urban and one rural Interstates and one recreational access route in Minnesota; the HCM states in the “Peak Hour and Analysis Hour” section within Chapter 8:

Customary practice in the United States is to base rural highway design on an hour between the 30th- and the 100th- highest hour of the year. This range generally encompasses the knee of the curve (the area in which the slope of the curve changes from sharp to flat). For rural highways, the knee has often been assumed to occur at the 30th-highest hour, which is often used as the basis for estimates of the design-hour volume. For urban roadways, a design hour for the repetitive weekday peak periods is common.

Past studies [cites 1982 and 1979 references] have emphasized the difficulty in locating a distinct knee on hourly volume curves. These curves illustrate the point that arbitrary selection on an analysis hour between the 30th- and the 100th-highest hours is not a rigid criterion and indicate the need for local data on which to base informed judgments.

HCM 2000 Exhibit 8-9 gives the proportion of AADT occurring in the “analysis hour” for five types of roads in Florida, the “K-factor” values ranging from 0.091 for urbanized to 0.100 for

1 A 2.0% per annum traffic growth value was assumed and it would appear a base figure of 12% of heavy vehicles – whether this was varied by traffic flow is unknown, or the assumed directional split ratio. It is presumed that the EEM results were based on a number of TRARR simulation runs at different traffic volumes and a volume-delay (plus vehicle operating costs) curve fitted to the results from which the annual results were then derived by applying the annual traffic flow profile.



rural undeveloped. These are unique to Florida and are possibly generally based on the 100th highest hour and achieving Level of Service C.

The HCM 2000 also states that:

Fifteen-min flow rates have been selected as the basis for most procedures in this manual. The relationship between the peak 15-min flow rate and the full hourly volume is given by the peak-hour factor (PHF). Whether the design hour is measured, established from the analysis of peaking patterns, or based on modeled demand, the PHF is applied to determine design-hour flow rates.

In practice traditionally within New Zealand peak flow factors have not been used for analysis of the design year flows, although the SIDRA default factor of 0.95 might sometimes be used for intersection analysis, and there is increasing use of simulation models (e.g. Paramics) in the urban context for which 5-minute flow profiles are often used.

HCM 2000 Exhibit 8-11 also gives the directional split for rural highways and two types of urban roads in Minnesota by the highest hour of the year (1st, 10th, 50th and 100th). For rural highways the range is 52-57% with 54% seeming a good weighted average; for urban circumferential a 53% split is given except for 50% for the 100th highest hour; for urban radial a 66% split is given for the 1st and 10th and 65% for the 50th and 100th highest hours.

Exhibit 8-12 gives the peak directional volumes as a percentage of the two-way AADT for multi-lane freeways using it appears a short-term count generally circa 1984 although the source is referenced as 1978!

It is considered then that the HCM data are generally old and probably relate to multi-lane Interstate highways and so are not so likely to be transferable to the New Zealand context and accordingly the derivation of appropriate values using recent New Zealand continuous data is appropriate.

United Kingdom (UK) As later noted, the UK has various factors and estimates of their error for determining the current year AADT and for determining the design hour as a percentage of the AADT. It is expected that most of these relate to the multilane trunk road network and inter-urban highways and the relevance of the results to the New Zealand predominantly rural two lane two-way state highway network is questionable. Accordingly given the limited scope of this paper the author has not sought out the latest UK values; interestingly values based on 1955-1960 UK data indicated that the 30th highest design hour flow is in the range 9½ to 11½ percent of the AADT, similar to that in Figure 6.

Australia (Austroads) Section 2.1.2 of the Austroads (2009) Guide to Road Design Part 3: Geometric Design states

Design requirements for roads are typically assessed by reference to forecasts of Annual Average Daily Traffic (AADT). Design hour volumes may be derived by consideration of the flow pattern across hours of the year. A 30th highest hourly volume is often adopted as a design volume. In areas of high peak or seasonal demands, such as recreational or harvest routes, special consideration may be required. In the absence of such information, refer to Table 4.1 for suggested values for the design life of particular road elements or treatments [the table gives values from 20 to 50 years].

Section A.4.3 in Appendix A of the Austroads (2009) Guide to Traffic Management - Part 3: Traffic Studies and Analysis gives a (somewhat poorly reproduced) figure A 10 (typical relationships between hourly volumes and AADT) but with no indication of the source. Fortunately the same figure is produced in a better manner in the Austroads (2007) Guide to Traffic Management - Part 6: Intersections, Interchanges and Crossings which gives the source as the Austroads (2004) Guide to Traffic Engineering Practice - Part 3: Traffic Studies, but unfortunately despite the fact that the new guides refer extensively to the other GTEP series, and despite the wish to the contrary of practitioners in New Zealand, Austroads has withdrawn all the former superceded guides from their online publications.

GTM Part 3 states that:



“The 30th highest hourly volume (denoted as 30 HV) is often used in designing rural roads…Nevertheless, the 30 HV may be inappropriately high for predominantly recreational routes, and an 80 HV or 120 HV may be chosen. In these cases the choice of DHV often needs special economic consideration….. On urban roads that are subject to pronounced peaks, it may not be appropriate to establish capacity analysis or design on a full peak-hour flow. This is because higher flows for shorter periods (e.g. 15 minutes) may result in unacceptable congestion for even a short period. The peak 15 minutes flow rate, converted to an equivalent hourly rate, may be used in such situations. Alternatively, a peak-hour factor (PHF) can be specified for the site and the full hour flow is divided by PHF to give a higher design volume to cater for possible heavier congestion. Further details of the method of estimating DHV can be found in Vaughan (1968).”

GTM Part 6 states that:

“In rural areas, a design hourly volume is estimated from the traffic patterns peculiar to the given road and area. This can vary from the 30th highest hour to the 120th highest hour depending on the type of route. A guide to the most economical design hour can be gained from a plot of hourly volumes from a continuous count station, usually expressed as a percentage of AADT, against the number of hours with a volume greater that the ordinate.

The resulting graph (see Figure 6.27), for example will usually have two portions – a steep part near the origin, and a flatter part as the number of hours increases. The design hour can then be estimated from the intersection point of the slopes of the two sections of the plot.”

However the GTM figure belies the suggested “intersection point of the slopes” approach in that it appears to result in a 15th to 30th design hour, and the literature usually states that typically it is not economical to design for the 30th highest hour for recreational rural routes.

The Austroads publication AP-C87-08 Glossary of Austroads Terms, 3rd edition December 2008 includes in its definition of the ‘highest hourly volume (HHV)’, “The 30th and 80th highest hourly volumes (denoted as 30 HV and 80 HV respectively) are commonly used parameters in assessing the design volume for setting the capacity of a traffic facility.” The Glossary definition of ‘nth highest hourly volume’ furthermore states that “30 HV … is often used as a representative traffic volume for road design, especially rural roads”, but there is no other mention of 80 HV in the Glossary or indication as to what situations it is commonly used rather than say the 30 HV.

The GTM figure shows highly varying results but unfortunately gives no indication from whence it came. Considerable effort was made to track down likely sources including Vaughan 1968



(noted but not given in the 1988 edition of the Austroads Guide to Traffic Engineering Practice - Part 3: Traffic Studies), but it gives a method of estimating the 30th highest design flow from five one-week (168 hours) random counts during the year, which is considered to be impractical. A number of other articles from the early 1960s were reviewed, but the Taylor and Young (1988) textbook was not reviewed nor the NAASRA 1982 Guide to Traffic Counting in State Road Authorities which potentially might be the source for the GTM curves.

Finding It is evident from the brief examination of key guidelines and manuals, that it is appropriate to ascertain what the corresponding typical curves might be for New Zealand rural highways, particularly those with a significant proportion of recreational traffic.

The next sections of this paper relate to the processing and analysis of recent continuous traffic data on New Zealand state highways (downloaded from the NZTA Traffic Monitoring System (TMS) and the findings of the analysis.

DATA PROCESSING AND ANALYSIS Over the years the author has developed a variety of firstly computer programs and then spreadsheets to process, analyse and report the continuous traffic monitoring sites in particular. In the end the approach chosen was to base the data analysis on downloading the exported quarter hour flows and to process a single site-year, with a single spreadsheet that could handle the three primary different types of sites (count, length, axle). The results would then be copied and pasted as values into a results spreadsheet, and therefore to reduce repetition the analysis spreadsheet had to be developed to its more-or-less completed state before processing of the exported TMS data could proceed. Naturally there was some compromise needed, and the analysis spreadsheet was enhanced as the project proceeded, and in one case simplified to increase the processing speed which was a major issue.

The input data consisted of the exported data from TMS which was produced using the Excel option, chosen manually although it had been hoped that the email option could be used or that the New Zealand Transport Agency (NZTA) would supply the data. Only site-years with no more than three missing years were selected for the years 2003 to 2008 inclusive, with a preference for years 2004, 2006 and 2008 as it so happened (refer Appendix A).

The data were copied into the analysis spreadsheet which included limited information for each site, including the AADT used as the basis for checking the (minimum) daily flow and with an assumed hourly flow profile low hourly two-way flows were highlighted using conditional formatting. The (hour ending) hourly flows were also manually checked and if need be changes to the “countif” criteria changed or the data edited. Some generic problems were noticed including a problem for some of the Central Otago local continuous sites whereby the midnight two-way flow for a week was downloaded as the daily flow and not the quarter hour flow, but this was easily spotted and corrected. Some sites appeared affected at times from snow and roadworks or other incidences (for example, three SH1N sites were affected on Monday 16 February 2004, suggesting a major road closure that might have been the Manawatu floods, while some South Island sites were affected on Monday 12 June 2006).

It had been thought that the odd missing day could be replaced by estimating but this idea was soon dropped and if the missing day(s) were deemed critical, then the site-year was excluded (for example for one site the only missing days were the very busy period 15-19 December).

The key outputs from the analysis spreadsheet were the four parameters for the 10th, 30th, 50th, 100th and 200th highest hourly flows, the frequency distribution for flows in 0.5% AADT bands, and the average hourly flow of use of the site-year was subsequently chosen for peak traffic flow analysis.

The four parameters were the two-way hourly flow expressed as a percentage of the AADT, the adjusted directional split, the adjusted percentage of heavy vehicles, and the two-way hourly heavy vehicle flow expressed as a percentage of the HV AADT. In each case the values were an average of the n-5 to n+5 hourly flow data, with the occasional value excluded as otherwise a more complex formula would have been needed; the adjustment was to ignore the highest and lowest values when averaging, and the output directional split was based on the absolute



directional ratio since in some cases the peak direction varied for the eleven hours. Note that the definition of heavy vehicle as derived from the four standard length bins (and the current vehicle axle-based classification scheme) was that as currently defined in TMS although the spreadsheet was setup to accommodate any future changes on an individual (dual loop) site basis.

The peakiness of the design hour flows was not derived, since extracting the quarter hour flows for the peak hour would have severely compromised processing speed, the hourly flows are always hour-ending and the New Zealand approach is to base on the peak hour and not the peak quarter hour as might be more commonly applied in North America. Note also that the proportion of following vehicles is not currently collected or recorded in the TMS and so was not able to be analysed.

The two-way hourly flow frequency distribution was derived for 0.5% AADT bands from 0 to 15% of the AADT based on the observed number of hours (with AADT calculated based on the observed number of valid ADTs).

The average hourly flows were computed for each hour for the average Monday-Thursday; Friday; Saturday; and Sunday/Holiday. Holidays included the appropriate anniversary public holiday (apart for some of the southern sites) and included the Christmas-New Year period but did not include Easter Saturday and Sunday nor the eve of public holidays (apart from 24 December). The averages were for each direction separately and combined (two-way) and the two-way averages given for each length bin (the 14 classes for the odd axle site were assigned to the four length bins) plus the derived light and heavy vehicle flows.

RESULTS SPREADSHEET Within the results spreadsheet the site category for each site was assigned based on the previous research work undertaken by the author in conjunction with Dr M Kelly Mara; however for some of the newer local continuous sites (principally in Northland and Central Otago and Southland) the category was initially guessed as being one of the following: urban Auckland; urban other; rural urban fringe (peri-urban); rural strategic; rural recreational winter; rural recreational summer.

This categorisation is based on the median weekly hourly flow profile and not on the basis of seasonal variation (week factors) or annual hourly flow distribution. The categories are strictly labels, used arbitrarily to describe the mathematical relationship identified from the hierarchical statistical clustering (dendogram) technique used (refer Wanty & Mara, 1994). Urban Auckland primarily consists of sites on the Auckland motorway network (prior to the ALPURT and SH 20 extensions), while urban other consists of some sites on other motorways and some on urban arterials outside of Auckland, none of which pertain to the CBD or commercial roads. Peri-urban (formerly rural urban fringe) historically related to sites on the outskirts of Auckland and Wellington which exhibited distinct weekday morning and evening peaks but which had different weekend flow characteristics from urban arterial sites. Rural recreational summer sites were those with particularly higher flows in summer even though most rural strategic sites also have higher summer flows. Rural recreational winter sites tend to be near the centre of the North Island or by the Southern Alps, and are influenced by the winter skiing season.

HOURLY FLOW FREQUENCY DISTRIBUTION The graphs below give the distribution of hourly flows for some selected sites.

The profiles are useful for ascertaining the delay (and vehicle operating costs) for each hour of the year and subsequently for future years where there is a known relationship (one that has been derived) between the hourly flow and delay. The hourly flow profiles were first derived in New Zealand in the late 1980s and the author used to produce an annual report for each continuous telemetry site which included this output (refer Silvester and Wanty,1990, and the example tables in Appendix B). They were applied by other researchers in economic models, including estimation of the annual cost of delays at one lane bridges (National Roads Board, Delays and Conflicts at one lane Bridges: cost estimation for bottlenecks, RRU occasional paper by L R Saunders, November 1988) – see also Bennett and Saunders 1986.



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Figure 1: Frequency Histogram – rural strategic sites (type A).

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Figure 2: Frequency Histogram – rural strategic sites (type B).

While Figures 1 and 2 seem fairly homogeneous, close inspection reveals some significant differences. Importantly the two types were basically selected based on the results and not on prior knowledge, with no predictive assessment being undertaken or attempt to, subjectively or objectively, divide these rural strategic sites into a ‘better’ arrangement of sub-groups.

As shown here the type “A” rural strategic sites are simply those with fewer hours in the year in the lowest (0.0-0.5 %AADT) hourly flow range than in the next lowest (0.5-1.0 %AADT) hourly flow range.



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Figure 3: Frequency Histogram – rural recreational sites (summer and winter).

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Figure 4: Frequency Histogram – urban and peri-urban sites.

Inspection of Figures 3 and 4 reveals that urban arterial sites tend to have a more pronounced peak than rural sites, while rural recreational sites have a greater spread (more hours at very low flows, a less pronounced peak at 7 %AADT and more hours at comparatively high flows).

It is to be hoped that in time, once better validation procedures are implemented in TMS in conjunction with incentives to minimise the extent of missing data for the continuous sites (particularly ones deemed to be “key”), that this graphical output (and the percentage AADT graph) will be incorporated in TMS.

In examining the temporal stability of the curves, five years were analysed for one site (SH1N Warkworth) and two for another (SH 1S Gore) with the results shown in figure below.



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Figure 5: Frequency Histogram – temporal stability for two sites (Warkworth and Gore).

This shows a very stable relationship for the Warkworth site in particular.

PERCENTAGE OF AADT The parameter traditionally tabulated and graph is the design hour expressed as a percentage of the AADT. The figures that follow show the results for the 10th, 30th, 50th, 100th and 200th highest hourly (hour ending) flow.

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Figure 6: Percentage AADT –average for different site category groups.

Inspection of Figure 6 above confirms the finding that rural recreational sites have design hours which are greater as a percentage of AADT than rural strategic sites, and urban sites have the flattest curves and lowest design hour percentage flows.



Astonishingly immediately after completing the analysis the author found in his 1986/87 examination paper from the Institute of Transport Studies, University of Leeds some UK values given for exactly the same five analysis design hours. In the above figure and those below, rural strategic sites have been split by their AADT, with type 1 comprising AADT < 5000, type 3 > 10000 and type 2 in between. Warkworth is the first township north of Orewa and north of the motorway to the north of Auckland and represents the average of the five years analysed for the same site.

In examining the temporal stability for the Warkworth site, the range in the %AADT figures was 0.8%, 0.5%, 0.4%, 0.3%, 0.2% for the 10th, 30th, 50th, 100th and 200th highest design hours respectively (the %AADT was about 13 % and 11½ % for the 10th and 200th highest design hours respectively). This is much less variation for a site than between sites in the same category - the UK values had a co-variance of 9% for the 200th highest design hour for both main-urban and inter-urban sites, compared to the 0.8% observed co-variance for Warkworth.

DIRECTIONAL SPLIT The directional split ratio is the average of the absolute ratios excluding the top and bottom values.

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Figure 7: Directional Split ratio –average for different site category groups.

The directional split / ratio generally varies between 0.56 and 0.61 regardless of the design hour chosen or site category; it is higher for the winter recreational sites which could perhaps be attributed to directional flows occurring each winter weekend as motorists head back from the ski fields to the main cities of Auckland, Wellington and Christchurch.

PERCENTAGE OF HEAVY VEHICLES (HV) The graphs below show a relatively constant percentage of heavy vehicles regardless of the design hour chosen, apart for the low volume rural sites. What the graphs do not immediately show is that the percentage of heavy vehicles in the design hour is typically much less than the percentage of heavy vehicles for the whole week / year. This can be deduced however from the graphs of the percentage of HV AADT noting that these are lower than the corresponding percentage of AADT (and less than the annual average %HV were these values to be examined).



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Figure 8: Percentage of Heavy Vehicles –average for different site category groups.

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Figure 9: Heavy Vehicles as a % HV AADT –average for different site category groups.

UNI-DIRECTIONAL ONE-WAY SITES For two Auckland urban motorway sites, the analysis was undertaken on a directional basis (many motorway sites in TMS are processed on a directional basis in the first instance).

For the normal two-way situation the two sites had almost identical %AADT figures, the SH16 Grafton site being 0.1% less than the SH1N Panama Road site in all five design hour instances.

The %AADT for all four uni-directional sites were greater than for the two-way sites, and varied by direction, the greatest difference compared to the two-way results being about 2.7%. This is not insignificant, and suggests that where a uni-directional approach is more appropriate then applying the ‘usual’ adopted two-way values is probably inappropriate. The difference is further



highlighted in the frequency histogram which shows that the uni-directional sites exhibit a greater proportion of peak flows compared to the two-way sites.

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Figure 10: Frequency Histogram – two Auckland urban motorway sites by direction.

For situations where a busy highway has a bottleneck constraint such as a merge from two lanes to one lane in one direction, then it might be appropriate to base the appropriate design hour flow (and frequency histogram) on an analysis of the directional flows rather than the two-way flows.

It is also interesting that in the Wellington region, passing lanes are sometimes closed at the very busiest times, but this is not necessarily the case in the Auckland region (for example the SH1N ALPURT toll highway over the Christmas – New Year 2009/10 period). Furthermore in the past one or two years some of these passing lanes on SH 1N in the Wellington region that were closed at these busiest times have been permanently removed when a wire rope median barrier has been installed for safety reasons (prevent head on collisions and consequential severe injuries and major traffic delays).

SUMMARY AND RECOMMENDATIONS It is evident that aside from the trunk highway network in the UK, and perhaps for certain highways for some States that have guidelines which the author has not uncovered in his limited search of the current main national guides, there is a gap in the publishing of appropriate design hour flows and associated parameters for use in strategic planning of highways.

To a limited extent, the work personally undertaken by the author during his Christmas – New Year 2009/10 break has closed the knowledge gap; however it also reveals that more rigorous assessment of certain types of rural highways in particular appears warranted, given the significant differences between the two seasonal types of rural recreational sites and some rural strategic sites.

Accordingly it is recommended to investigate more closely sites which may or potentially may be considered to be rural recreational sites. This could include also determining the 75th,125th, 175th and 440th highest hourly flows (the 80th and 120th are mentioned in earlier Austroads guides), as the 125th highest hour is the NZTA proposed design hour for passing lanes, while 440 hours is equivalent to 5% of 8760 (8784) annual hours (and 175 hours is about 2% of the annual hours).

It is recommended to examine more the uni-directional results, and to revise the NZTA provisional Passing and Overtaking guidelines including the following amendment:



In the absence of any traffic flow data, for urban strategic state highways, assume a 60/40% direction split with a peak flow of 10.5% AADT [use 12.5% for peri-urban sites]. This flow should not be exceeded for 95% of hours during the design year.

It is also recommended that the percentage of following or free vehicles be collected for the NZTA continuous sites and also the speed where appropriate to facilitate calculating the level of service at the design hour.

To assist practitioners it is recommended that the NZ Transport Agency’s Traffic Monitoring System (TMS) be enhanced by producing appropriate tables and graphs for each continuous site on an annual basis, as used to be done by the author some twenty years ago (refer to an example of one of the outputs given in Appendix B).

REFERENCES Bennett C J, Saunders L (1986). The representation of traffic volume data for use in economic analyses. Proceedings 13th ARRB 1986 Conference (5th REAAA Conference), 13(7) pp 80-91.

Silverster D I, Wanty D K (1990). New Zealand Traffic Data Collection System. Proceedings 15th ARRB Conference, Darwin, 1990, 15(6) pp 251-287.

Taylor M A P, Young W (1988). Traffic Analysis: New Technology and Solutions. Hargreen Publishing Co: Melbourne and Edward Arnold: London.

Vaughan R J (1968). The estimation of highest hourly volumes. Proceedings 4th Australian Road Research Board Conference, Melbourne, 1968, 4(1) pp 633-644.

Wanty D K, Mara M K (1994). Traffic Count Accuracy and Monitoring Programmes. Proceedings IPENZ Annual Conference, Nelson, 1994, Volume 2 pp 90-95.

ACKNOWLEDGEMENTS The author acknowledges the support of the MWH New Zealand Limited in preparing and presenting this paper, the assistance of the New Zealand Transport Agency in supplying the TMS data, and ARRB Group in providing the Vaughan 1968 reference article.

AUTHOR BIOGRAPHY David joined the Ministry of Works and Development Head Office after completing his BE and ME in Civil Engineering at Christchurch. He was awarded a National Roads Board scholarship and completed a MSc in Transport Planning & Engineering at Leeds, UK. In 1994 he left the then Transit NZ to join Traffic Design Group Ltd, before working at the Land Transport Authority in Singapore in late 2000 as their (carless!) Senior Road Safety Engineer. After returning to Wellington in early 2005 he joined MWH becoming the Discipline Leader for Traffic Engineering. For over 20 years David has been closely involved in traffic monitoring, developing the National Traffic Data Collection System hardware & software, authoring the Traffic Count Guideline and advising NZTA National Office on their Traffic Monitoring System. He is passionate about data quality, analysis, reporting and undertaking applied research to meet the needs of practitioners.



APPENDIX A: TABLE OF PROCESSED SITES SHOWING VALID DAYS # SiteID Name Type 03 04 05 06 07 08 Comment URBAN 1 01N00274 M’karamea LEN 365 01N00347 Wellsford Count 365 01N00369 Warkworth Count 365 365 365 365 365 Processed all *01N00389 Grand Dr Count 365 Ex 01Ad0000 5 016d9001 Grafton Count 366 by direction 01Nd0440 Panama Rd Count 365 05000010 Taradale LEN 365 00200937 Rimutaka LEN 363 01N01076 Patterson St Count 365 10 07400006 Cranford St LEN 365 08800010 St Leonards Count 363 Urban ish 06A00002 Frankton Count 361 Urban + rec 01S00861 Gore Count 364 366 14 01S00921 Tay St, I’gill LEN 365 RURAL ish 15 01000029 Takou Bay LEN 365 01200220 Brynderwyn LEN 363 1-11/13 Jan 01N00130 Ramseys br LEN 365 01N00212 Kawakawa LEN 365 01N00339 Wellsford LEN 365 20 *01700006 Hatfields LEN 365 Ex 01N00388 00200002 M’tawhiri LEN 363 00200091 Waihi LEN 363 00300085 Te Kuiti LEN 364 01N00580 Karapiro LEN 362 25 01N00620 Lichfield LEN 365 02700011 Kaihere LEN 362 00200141 Te Puna LEN 365 00200204 Ohinepanea LEN 365 00500034 Tarukenga LEN 365 30 03300030 Paengaroa LEN 365 00200428 Ormond LEN 365 00200627 Tangoio LEN 366 00500230 Te Pohue LEN 364 00300171 Tongaporutu LEN 365 35 00300267 Tariki LEN 364 00200755 Norsewood LEN 366 00300489 Man. Gorge LEN 365 00400133 Horopito LEN 363 00400226 Upokongaro LEN 365 40 01N00827 Hihitahi LEN 364 01N00930 Sanson LEN 365 01N00988 Ohau LEN 364 00200895 Clareville LEN 366 00600100 Hira LEN 364 45 01S00037 Blenheim LEN 364 06000040 Riwaka LEN 364 00700108 Lewis Pass LEN 365 12/6/06 01S00389 Dunsandel LEN 365 12/6/06 01S00522 St Andrews LEN 365 12/6/06 50 07300064 Springfield LEN 362 00600398 Punakaiki LEN 365 00700239 Ahaura LEN 365 00600882 Hawea south Count 363 00600997 Kawarau Falls Count 362 55 00800325 Alex – Clyde Count 363 00800336 Alex south LEN 365 01S00854 Gore east LEN 365 08500010 Inch Valley Count 363 08700015 West Taieri Count 365 60 08700065 Middlemarch Count 363



# SiteID Name Type 03 04 05 06 07 08 Comment 00601147 Winton LEN 366 62 09900027 Riverton Count 366

The annual frequency histogram was processed for those site-years with 0 (or some with 1) missing days.

There are also up to 20 other sites with years which had 0 or 1-3 days missing which were not processed.



APPENDIX B: ANNUAL OUTPUT REPORT EXAMPLE TABLE

typical peak design hour characteristics

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