INFR Sep 2019 SW Herts COMET Note Final Draft
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South West Hertfordshire Interpretation of COMET Model Results FINAL DRAFT Hertfordshire County Council County Hall Pegs Lane, Hertford Hertfordshire SG13 8DQ United Kingdom Telephone: +44 1992 555 555 Website: www.hertsdirect.org Date: 04/09/2019 Status: Draft Prepared By Matthew Newton Hertfordshire County Council Data Assistant County Hall Pegs Lane, Hertford Hertfordshire SG13 8DQ United Kingdom FINAL DRAFT Reviewed By Daniel Tarry Telephone: +44 1992 588 615 Senior Transport Planner Website: www.hertsdirect.org Date: 04/09/2019 Status: Draft Approved for Release By Sue Jackson Date 13/09/2019 Group Manager Transport Planning & Strategy Status Draft Reference 13/09/2019 Draft Issue 2 Hertfordshire County Council Contents 1 Introduction ............................................................................................................... 1 2 Model Assumptions .................................................................................................. 2 Infrastructure Assumptions ................................................................................. 2 3 Model Results ............................................................................................................ 3 Flow Differences ................................................................................................. 3 Volume Capacity Ratios ................................................................................... 12 Junction Delays ................................................................................................ 20 4 Conclusions ............................................................................................................. 39 Ordnance Survey Licence Ordnance Survey mapping included within this document annotated “© Crown copyright and database rights 2014 Ordnance Survey 100019606” is used in accordance with Hertfordshire County Council’s licence. You are not permitted to copy, sub-licence, distribute or sell any of this data to third parties in any form. FINAL DRAFT 13/09/2019 Draft Issue 2 Hertfordshire County Council 1 1 Introduction Hertfordshire County Council have developed a Countywide model COMET. This consists of a suite of models including a Variable Demand Model, Highways Model and Public Transport Model and has been used to test the cumulative impacts of Local Plan growth across the county. A new 2036 Forecast Model run was undertaken in early 2019 with districts Local Plan development assumptions as of Autumn 2018. Local Plan growth plus transport mitigation measures as identified by the districts and boroughs has been tested. Countywide results of the latest Local Plan Run 4 have been documented in the Forecasting Report. This note provides a more detailed assessment of the model results within the South West Herts area (encompassing Dacorum, Hertsmere, St Albans, Three Rivers and Watford) considering the cumulative impact of growth and potential transport schemes across this area and in other Hertfordshire districts. The highway assignment component of the COMET model suite is in SATURN. SATURN is a tool that suits the strategic geographical scale of COMET, however, does not enable investigation of detailed sections of the highway network (e.g. detailed junction or corridor assessment). At this stage, therefore, the results presented here should be interpreted as high- level indications of likely traffic conditions. The COMET model enables an interpretation of potential impacts across the whole area taking into account the influence of growth and schemes in other areas. The COMET model uses Passenger Car Units (PCUs) to represent general traffic. This is common practice for traffic modelling software. In COMET, cars and LGVs are coded as 1 PCU, HGVs are coded as 2.2 PCUs. In addition to the results presented in the main body of this note, detailed, district-based results, are presented in the Appendices: • Appendix B – Dacorum • Appendix C – Hertsmere • AppendixFINAL D – St Albans DRAFT • Appendix E – Three Rivers • Appendix F – Watford 13/09/2019 Draft Issue 2 Hertfordshire County Council 2 2 Model Assumptions Planning Assumptions Planning assumptions are as per the COMET Local Plan Run 4 and are listed in Table 2-1 below. This is based on Tables 5.1 and 5.2 of the COMET Forecasting Report. Table 2-1 COMET Model Local Plan Run 4 Planning Assumptions Dwellings Jobs 2014-20361 2014-2036 Dacorum 19,8592 1,4943 Hertsmere 16,7852 6,314 St. Albans 17,749 6,2134 Three Rivers 4,069 8,275 Watford 10,313 11,193 SWH Total 68,775 33,489 County Overall 114,540 62,728 Source Table 1.1 Comet LP4 Forecasting Report Final June 2019 1Includes as built in addition to local plan allocations and windfall allowance 2 Includes some speculative sites with currently no planning status 3 LEZ is coded in St Albans 4 LEZ jobs gain is counterbalanced by employment loss Infrastructure Assumptions A number of schemes which were deemed as committed or highly likely along with appropriate access points from the key developments were already coded into model. In addition, there are general schemes identified in Local Plan Infrastructure Delivery Plans and other studies such as the SWH Growth and Transport Plan and Maylands Growth Corridor Study to accommodate growth. The schemes included in the South West Herts area are listed in Appendix A. It should be noted that schemes have been included in the test regardless of their certainty level. Therefore, the model run includes a number of hypothetical conceptual schemes where no designs are yet available and therefore high level assumptions of their layout / impact have been used. As all the schemes have been modelled together it is not possible to isolate the impacts of individual schemesFINAL in this forecast run. DRAFT Given the strategic nature of the COMET model it was not possible to include some of the more minor changes to the highway network. Where scheme elements were not coded this is indicated in the table. 13/09/2019 Draft Issue 2 Hertfordshire County Council 3 3 Model Results Flow Differences Figure 3-1 and Figure 3-2 show the difference in flows between 2014 and 2036 models in the AM and PM peaks in South West Herts with green illustrating where flows increase and blue indicating where there are decreases in flow. This provides an indication of the impact of the planning data and growth information, alongside the impact of proposed schemes and mitigation schemes. As COMET also includes a Variable Demand and Public Transport model behavioural responses to congestion such as peak spreading and switching to other modes (especially rail) are also taken into account. It should be noted that flow differences are only shown where the highway network coding in both models matches and therefore changes in flow on new infrastructure such as new link roads, do not show up. Further detail for the key towns is given in the following pages. FINAL DRAFT 13/09/2019 Draft Issue 2 Hertfordshire County Council 4 FINAL DRAFT Figure 3-1 2036 - 2014 Actual Flow in South West Hertfordshire AM Peak (08:00 – 09:00) 13/09/2019 Draft Issue 2 Hertfordshire County Council 5 FINAL DRAFT Figure 3-2 2036 - 2014 Actual Flow in South West Hertfordshire PM Peak (17:00 – 18:00) 13/09/2019 Draft Issue 2 Hertfordshire County Council 6 The changes in flow between the base and future year are a combination of growth in the numbers of dwellings and jobs and the impact of new infrastructure schemes. Key changes are outlined by District below, more detailed plans are included in the appendices. 3.1.1 Key Flow Changes in Dacorum (see Appendix B for detailed plans) There is an increase in traffic flow on the A41 between Tring and Berkhamsted. This increase is largest northbound in the AM and southbound in the PM. This is a result of housing and employment growth in the area. 3.1.1.1 Hemel Hempstead: Numerous roads in the South West Hemel Hempstead are forecast to experience a decrease in traffic volume. This is due to the scheme included to convert Fishery Road into a cycle and bus only road. This reduces capacity in the area and makes it less attractive to through traffic, causing traffic re-distribution. There is a significant increase in traffic volume to the east of Hemel Hempstead as a result of development in the Maylands and East Hemel area. This includes an increase in traffic leaving the M1 to join the A414. The link road coded in the north Hemel area causes re-routing of traffic in the Potten End Area LP Run 4 shows approximately 300 PCUs less on the A414 St. Albans Road, in both the AM and PM peaks, when compared to LP Run 3. This is because of a bus lane in each direction being coded into the model in line with the GTP proposals for a sustainable travel corridor. This bus lane reduces the road from a dual carriageway to a single carriageway, reducing the capacity of the road. This causes increased delay times and encourages traffic to re-route onto alternative roads. To the south of Hemel Hempstead, LP Run 4 predicts the re-routing of traffic onto more minor roads in the AM peak. This is as a result of traffic avoiding the delays on the A41 approach to M25 J20. 3.1.1.2 Berkhamsted: There is a reduction in the volume of traffic traveling southbound and northbound through Berkhamsted in both the AM and PM peaks. This is a result of the signalisation of the junction of A416 Kings Hill FINALWay / A416 Kings Road / Shooters DRAFT Way. This signalisation has been implemented since the 2014 Base Year was created. The scheme is designed to improve the pedestrian crossing facilities