VALP Modelling

BCC

NE Bucks Local Plan Tests -Technical Report

TN02 | 2

30/05/19

BCC

NE B ucks Loc al Plan T ests -Tec hnical Report BCC

NE Bucks Local Plan Tests -Technical Report

VALP Modelling

Project No: BRJ10150 Document Title: NE Bucks Local Plan Tests -Technical Report Document No.: TN02 Revision: 2 Date: 30/05/19 Client Name: BCC Client No: BCC Project Manager: Mily Parveen Author: Catherine Hill File Name: M:\Transport Modelling\BRJ10150 VALP Model Runs\Technical Work\Reports\Countywide modelling report\Countywide Modelling Report- VALP 290519.docx

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Limitation: This document has been prepared on behalf of, and for the exclusive use of Jacobs’ client, and is subject to, and issued in accordance with, the provisions of the contract between Jacobs and the client. Jacobs accepts no liability or responsibility whatsoever for, or in respect of, any use of, or reliance upon, this document by any third party.

Document history and status

Revision Date Description By Review Approved

0 28/02/19 Draft CH TW MP

1 09/04/19 Revision after client comment CH/TP MP MP

2 30/05/19 Revision after client comment CH/TP MP MP

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Contents 1. Introduction ...... 4 1.1 Background ...... 4 1.2 Scope of study ...... 4 1.3 Development scenarios ...... 4 1.4 Mitigation options ...... 5 1.5 Structure of report ...... 5 2. Modelling Methodology ...... 6 2.1 Overview ...... 6 3. Development Scenarios ...... 8 3.1 Overview ...... 8 3.2 Development summary...... 8 3.2.1 Do Something ...... 9 4. Mitigation options ...... 10 4.1 Overview ...... 10 4.2 Option generation ...... 10 4.3 Options for appraisal ...... 10 5. Results ...... 12 5.1 Overview ...... 12 5.1.1 Congestion ratio ...... 12 5.1.2 Change in travel time ...... 12 5.2 Summary of impacts ...... 14 5.2.1 DM Scenario ...... 14 5.2.2 DS scenario ...... 16 5.2.3 DS1 scenario ...... 18 5.2.4 DS2 Scenario ...... 22 5.2.5 DS3 Scenario ...... 26 5.2.6 DS4 Scenario ...... 30 5.2.7 DS5 Scenario ...... 34 5.3 Bletchley Bypass Removal Sensitivity Test...... 38 5.3.1 DS Scenario ...... 38 5.3.2 DS1 Scenario ...... 40 5.3.3 DS2 Scenario ...... 42 5.3.4 DS3 Scenario ...... 44 5.3.5 DS4 Scenario ...... 46 5.3.6 DS5 Scenario ...... 48 6. Summary and conclusion ...... 50 6.1 Summary of results ...... 50 6.2 Summary of individual development impacts ...... 51 6.3 Conclusions ...... 52

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Appendix A. Phase 3 Methodology and Assumptions (taken from the Phase 3 Technical Note, Section 2) Appendix B. Congestion Ratio Plots Appendix C. Change in Travel Time Plots

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1. Introduction

1.1 Background

Jacobs is framework consultant to the Transport for Buckinghamshire Alliance (TfB) between Ringway Jacobs and Buckinghamshire County Council (BCC). Under the terms of this contract, Jacobs is commissioned to undertake transport planning, modelling and appraisal projects on behalf of BCC.

Jacobs has previously been commissioned to undertake transport modelling assessments of the impacts of Local Plan developments in Buckinghamshire. Work on the first, second and third phase of the Countywide Local Plan Modelling project, which used a strategic transport model of Buckinghamshire, was undertaken and completed as part of that commission. Further details of this work can be found in the Phase One Forecast Modelling Report 1, the Phase Two Forecast Modelling Report 2 and the Phase 3 Technical Note 3.

Following the Vale of Aylesbury Local Plan (VALP) Examination in Public (EiP), Buckinghamshire County Council (BCC) and Aylesbury Vale District Council (AVDC) have asked Jacobs to undertake further modelling using updated Aylesbury and Countywide strategic models, as well as local junction models of Buckingham, in order to assess the impacts of the Local Plan in more detail.

This report will build on previous Countywide modelling as AVDC have requested an assessment of new sites around Milton Keynes through the use of new forecast scenarios tested through the Countywide model. The additional sites for assessment are at Eaton Leys and Salden Chase Extension with a revision in development quantum at the previously assessed Shenley Park site.

The Phase 3 countywide ‘Do something’ (DS) scenario will be retained as a comparator for the purpose of this modelling, and five further DS scenarios will be developed.

1.2 Scope of study

The most recent Countywide modelling undertaken was the Phase 3 work, in which ‘Do minimum’, ‘Do something’, and ‘Do something with mitigation’ scenarios were developed. To test the impact of new combinations of development in North East Buckinghamshire, adjacent to Milton Keynes, five new ’Do something’ (DS) scenarios have been developed (further detail of the scenarios is provided in section 1.3 and section 3). For each of the above scenarios, a ‘with mitigation’ version was also produced which includes the list of mitigations as per the Phase 3 run 1 mitigation scenario.

This study does not supersede or replace any detailed modelling work that has been done or will be required in future in assessment of the impacts of individual developments. The purpose of this report is only to assess cumulative impacts of the changes in development proposals and identify areas where these could be considered significant in terms of travel time differences.

1.3 Development scenarios

For the Countywide model, three forecast scenarios were developed during the first and second phases of work, in cooperation with BCC and AVDC. These comprised of a 2033 DM scenario which included the projected planning completions to 2033 across Buckinghamshire, as well as committed development (some of which may form part of the local plan proposals), and two DS scenarios which included DM development plus additional non-committed local plan developments across the county.

1 Jacobs. 2016. Countywide Local Plan Modelling: Forecast Modelling Report Phase 1. 2 Jacobs. 2017. Countywide Local Plan Modelling: Forecast Modelling Report Phase 2. 3 Jacobs 2017. Countywide Local Plan Modelling: Forecast Modelling Technical Note 3

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For Phase 3, the DM development scenario remained unchanged, and the DS scenario was updated to reflect the revised local plan growth for Aylesbury Vale.

For this VALP work, the model had two additional zones created (for the new development sites) and five further DS scenarios developed. The DS scenarios were created following the same methodologies and assumptions as for the Countywide Phase 3 modelling, which are detailed in Appendix A

Further details of the forecast scenarios are provided in section 3 of this report. The revised DS scenario will then be used to develop the DS with mitigation scenarios.

1.4 Mitigation options

For Phase 3 of the Countywide modelling two separate mitigation schemes were developed, referred to as Phase 3 run 1 and Phase 3 run 2. For the purposes of this VALP Modelling report a ‘with mitigation’ version has been produced for each new DS scenario which includes the list of mitigations as per the Phase 3 run 1 mitigation scenario.

As part of the current iteration of VALP modelling work, an additional sensitivity test has been developed, with the aim of reviewing the impacts on the road network if Bletchley Bypass is not implemented as part of the package of mitigation schemes. The assumptions for this sensitivity test are the same as those made for the Phase 3 run 1 scenario, apart from the exclusion of Bletchley Bypass from the forecast network. Throughout the report, this sensitivity test will be referred to as the Bletchley Bypass removal sensitivity test.

Table 4.1 in section 4 sets out the mitigation measures included in Phase 3 run 1 and the Bletchley Bypass removal sensitivity test.

1.5 Structure of report

The structure of this report is as follows: • Section 1: Introduction – Outlines the background and scope of the report. • Section 2: Modelling methodology – Describes the development of the forecast scenarios. • Section 3: Development scenarios – Summarises the land use changes • Section 4: Mitigation options – Summarises the option sifting process and mitigation options taken forward for testing and appraisal. • Section 5: Results – Presents the results of modelling work for each model area and scenario assessed. • Section 6: Summary and conclusion – Summarises the results of the modelling work.

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2. Modelling Methodology

2.1 Overview

This section sets out the modelling methodology adopted to develop the forecast scenarios. Five VALP DS scenarios will be developed which reflect development sites around Milton Keynes. The development sites are included as separate model ‘zones’, with their approximate locations shown in the figure below.

Shenley Park

Eaton Leys

Salden Chase Extension

Figure 2.1 Development zone location

The new VALP DS scenarios are as follows: • DS1 – the same as the existing ’Do something’ from Phase 3, but with Shenley Park included at 1,800 dwellings instead of 1,600 dwellings as in the existing Phase 3 DS. This also includes any relevant transport infrastructure for the development • DS2 – as per DS1 above, but with the 1,400 dwellings at Shenley Park and the addition of 1,200 dwellings at Eaton Leys • DS3 – the same as DS1 above but with 1,200 dwellings at Shenley Park and the addition of 1,100 dwellings at Salden Chase Extension • DS4 – the same as the previous Countywide Phase 3 ‘Do something’ but with Shenley Park removed and the addition of 1,200 dwellings at Eaton Leys • DS5 - the same as the previous Countywide Phase 3 ‘Do something’ but with Shenley Park removed and the addition of 1,100 dwellings at Salden Chase Extension

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For each of the above scenarios, a ‘with mitigation’ version will also be produced which includes the list of mitigations as per the Phase 3 run 1 mitigation scenario. The Bletchley Bypass removal sensitivity test, which is the same as the run 1 mitigation scenario but with Bletchley Bypass removed, will also be produced for each of the above scenarios.

In all other respects, the development of the forecast scenarios is consistent with the methodologies followed in Phase 3. The detail of those methodologies is provided in Appendix A.

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3. Development Scenarios

3.1 Overview

This section sets out the revisions made to the DS forecast scenario, in line with the updated land use information provided by BCC. For each development scenario, forecast housing and employment growth has been added to the existing 2013 base land use information to generate a new development quantum.

3.2 Development summary

Table 3.1 provides a summary of the Countywide Model Phase Three DS land use assumptions and the absolute differences between the employment and housing figures for the new VALP DS scenarios.

Future scenario (2033) Summary details

Unchanged from phase three and comprised of: • 9,416 houses and 24,265 jobs in Aylesbury Vale; • 1,278 houses and 0 jobs in Chiltern; Do Minimum (DM) ‘No development’ • 1,297 houses and 1,619 jobs in South Bucks; and • 2,180 houses and 6,011 jobs in Wycombe. Total: 14,171 houses and 31,895 jobs.

As Phase 2 but; • A reduction of 2,143 houses in Aylesbury Vale (including 1,600 houses at Shenley Park) • An additional 522 jobs in Chiltern; Countywide Phase 3 Do Something (DS) • An additional 2,199 jobs in South Bucks; and • An additional 1,360 houses and 1,070 jobs in Wycombe district. Total: 52,373 houses and 48,624 jobs.

As Phase 3 DS with: VALP Do Something 1 (DS1) • Addition of 200 houses at Shenley Park. Total: 52,573 houses and 48,624 jobs

As Phase 3 DS but with: • Addition of 1,200 houses at Eaton Leys; VALP Do Something 2 (DS2) • Reduction of 200 houses at Shenley Park. Total: 53,373 houses and 48,624 jobs

As Phase 3 DS but with: • Reduction of 400 houses at Shenley Park; VALP Do Something 3 (DS3) • Addition of 1,100 houses at Salden Chase Extension. Total: 53,073 houses and 48,624 jobs

As Phase 3 DS with: • Addition of 1,200 houses at Eaton Leys; VALP Do Something 4 (DS4) • Reduction of 1,600 houses at Shenley Park. Total: 51,973 houses and 48,624 jobs

As Phase 3 DS with: VALP Do Something 5 (DS5) • Addition of 1,100 houses at Salden Chase Extension;

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Future scenario (2033) Summary details

• Reduction of 1,600 houses at Shenley Park. Total: 51,873 houses and 48,624 jobs

Table 3.1 Revised forecast scenarios

Compared with the Phase 3 DS scenario figures, DS4 and DS5 show an overall decrease in housing numbers whereas DS1, DS2 and DS3 show an increase.

3.2.1 Do Something

Within the county, the DS scenarios contains the DM land use quantum plus the revised local plan development scenario for Phase 3 and the new quantum at the development sites. For all areas outside of Buckinghamshire, growth in employment and housing is consistent with NTEM levels of growth. Table 3.2 provides a summary of the DS scenarios.

Location Totals

• DM commitment plus 20,207 houses and 6,069 jobs, including 1,600 houses at Shenley Park and no houses at either Eaton Leys or Salden Chase Extension (DS) • DM commitment plus 20,407 houses and 6,069 jobs, including 1,800 houses at Shenley Park and no houses at either Eaton Leys or Salden Chase Extension (DS1) • DM commitment plus 21,207 houses and 6,069 jobs, including 1,400 houses at Shenley Park, 1,200 houses at Eaton Leys and no houses at Salden Chase Extension (DS2) Aylesbury Vale District • DM commitment plus 20,907 houses and 6,069 jobs, including 1,200 houses at Shenley Park, 1,100 houses at Salden Chase Extension and no houses at Eaton Leys (DS3) • DM commitment plus 19,807 houses and 6,069 jobs, including 1,200 houses at Eaton Leys and no houses at either Salden Chase Extension or Shenley Park (DS4) • DM commitment plus 19,707 houses and 6,069 jobs, including 1,100 houses at Salden Chase Extension and no houses at either Shenley Park or Eaton Leys (DS5)

Chiltern District • DM commitment plus 3,847 houses and 522 jobs

South Bucks District • DM commitment plus 4,324 houses and 6,578 jobs

Wycombe District • DM commitment plus 9,824 houses and 3,560 jobs

Outside of Buckinghamshire • Capped to NTEM growth levels

Total within Buckinghamshire • DM commitment plus 38,202 houses and 16,728 jobs

Table 3.2 Do Something growth

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4. Mitigation options

4.1 Overview

This section describes the development of the mitigation scenarios and the selection of the schemes tested. Table 3.2 presents the final mitigation options included in each run of the mitigation model.

4.2 Option generation

As part of the Countywide modelling, a long list of schemes was put together by BCC in collaboration with the districts. This included a variety of highway improvements (upgraded roads, junction improvements, relief roads etc.) and an assortment of public transport schemes with the aim of encouraging a mode shift from car to sustainable transport (upgraded bus and rail facilities, improvements to the cycling network, public transport initiatives etc.).

The options were designed to address strategic issues identified in the Countywide modelling, as well as concerns of a more localised nature, tackling areas and facilities that could be enhanced and developed in order to reduce congestion and delay arising from the additional housing and employment developments across the county. The same scheme mitigation options (run 1) that were used in the Countywide Phase 3 modelling are being used in this work. The Bletchley Bypass removal sensitivity test includes the same schemes as the run 1 mitigation scenario, only with Bletchley Bypass removed.

4.3 Options for appraisal

Table 4.1 outlines each mitigation option taken forward for appraisal in Aylesbury vale after the sifting process was completed. The table also includes a separate column for the schemes included in the Bletchley Bypass removal sensitivity test.

Bletchley Bypass Run District Scheme name Scheme description removal 1 sensitivity test

The southern section of the Eastern Link Road will complete a new north-south, single carriageway road between the A418 Aylesbury Road and A41 Aston Clinton Eastern Link Road (South) Road, to the east of Aylesbury. Yes Yes The scheme will provide access to the Woodlands Development and will include an upgraded A41 Roundabout.

The Southern Link Road between the A41 Aston Clinton Aylesbury Road and A413 Wendover Road is already included in the Vale Southern Link Road without mitigation scenarios. However, as a mitigation Yes Yes (upgrade) option, this scheme was upgraded to dual carriageway standard, and includes a new roundabout and left-in left- out access junction.

This scheme seeks to extend the planned Stoke Stoke Mandeville Bypass Mandeville bypass (A4010 realignment) with a new single Yes Yes Extension carriageway road to meet the Southern Link Road at the A413 Wendover Road.

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Bletchley Bypass Run District Scheme name Scheme description removal 1 sensitivity test

The scheme includes implementing bus priority measures (e.g. bus lanes and priority at traffic lights). The A41 Bicester Road PPTC Yes Yes improvement will aim to significantly improve journey time reliability and increase the public transport mode share.

The scheme includes implementing bus priority measures A41 Tring Road PPTC (e.g. bus lanes and priority at traffic lights). The Yes Yes Improvements improvement will aim to significantly improve journey time reliability and increase the public transport mode share.

Stoke Road Signalised Signal timing optimisation has been carried out to better Yes Yes Junction accommodate demand at this junction.

Traffic calming between A418 and Stoke Traffic calming on Prebendal Avenue to reduce rat-running Yes Yes Mandeville between A418 and Stoke Road.

Aylesbury Town Centre This improvement aims to increase safety and enhance Pedestrian Network the public realm in Aylesbury Town Centre. Yes Yes Improvements

This scheme is designed to provide cost-effective off-road walking and cycling routes in an area of major growth. The project includes improving existing towpaths, the upgrade Grand Union Triangle Yes Yes of a public footpath to a bridleway and then implementation of connecting routes and some small-scale improvements.

A421 Roundabout Capacity improvements at the London Rd/ A421 Rbt and Yes Yes Capacity Improvements Gawcott Rd/ A421 Rbt to increase capacity. This scheme will implement a new grid road to the A421 New Grid Road in Milton adjacent to the V1 to discourage rat running through Yes Yes Keynes Whaddon.

This scheme consists of a new single-carriageway road Bletchley By-Pass Yes No joining the A421 and A4146 South West of Bletchley.

Table 4.1 Run 1 Mitigation and Bletchley Bypass removal sensitivity test options for Aylesbury Vale

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5. Results

5.1 Overview

The purpose of this section of the report is to present the modelling outputs from the new DS modelling forecast scenarios in so far as they affect the area of Buckinghamshire in the vicinity of the updated developments, i.e. around Milton Keynes and the A421 corridor. As with the previous phases of work, a set of model outputs have been produced to illustrate the impacts of the DS forecast scenarios compared with the Phase 3 DM as well as the DS with mitigation compared against the respective (non-mitigation) DS scenario.

It is important to note that the DS development scenario (with and without mitigation) models the cumulative impact of the revised local plan development scenario across the model, whilst the mitigated scenario also gives an indication of the overall impact of the included mitigation. As such, the narrative below focuses on the area as a whole in terms of travel time and congestion changes and does not distinguish between or attribute impacts to individual developments and mitigation schemes.

The majority of the commentary in this section is based on the model output from the updated DS scenarios (derived from revisions to the Phase 3 Countywide Model scenarios); however wherever necessary information has been supplemented with evidence from other modelling work and local knowledge. All the model outputs produced for this phase of work can be found in Appendix B and Appendix C of this note. A detailed description of the different types of output can be found below.

5.1.1 Congestion ratio

The congestion ratio plots show the ratio of the congested travel time to the free flow travel time on each modelled link. An increase in the congested travel time on a link is not only affected by increases in flow, but also by delays at the downstream junction. As a result, it is possible, where junctions are constrained, to see congestion on a particular link, without any significant increase in demand flow.

Links are plotted according to the following criteria:

Colour of the band Congestion ratio Interpretation

Transparent 1 Link experiences free flow conditions

Green 1-1.5 Travel times are up to 50% greater than in the uncongested situation

Yellow 1.5-2 Travel times are between 50% and 100% (i.e. two times) higher than in the uncongested situation Orange 2-4 Travel times are between 100% and 400% (i.e. two to four times) higher than in the uncongested situation

Red >4 Travel times are more than 400% (i.e. more than four times) higher than in the uncongested situation

Table 5.1 Congestion ratio criteria

5.1.2 Change in travel time

Plots of the change in travel time show the difference in congested link travel times between an altered and comparison scenario (for example DS1 and DM) as a percentage. The change is only shown for those links on which the congested travel is more than twice the free flow time in either scenario, i.e. for those links for which the congestion ratio is greater than 2 (and thereby marked with an orange or red band as described in Table 5.3 ensures that only those areas which experience relatively high levels of congestion are shown.

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The congested link travel time is the same as that used for the congestion ratio. It is worth noting that where an area is already congested in the comparison model, travel times will be more sensitive to smaller increases in trips.

Plots have been produced for the following 10 combinations of scenarios for all time periods:

Adjusted Scenario Comparison Scenario

DS1 DM

DS1 with mitigation DS1 (without mitigation)

DS2 DM

DS2 with mitigation DS2 (without mitigation)

DS3 DM

DS3 with mitigation DS3 (without mitigation)

DS4 DM

DS4 with mitigation DS4 (without mitigation)

DS5 DM

DS5 with mitigation DS5 (without mitigation)

DS1 Bletchley Bypass removal sensitivity test DS1 (without mitigation)

DS2 Bletchley Bypass removal sensitivity test DS2 (without mitigation)

DS3 Bletchley Bypass removal sensitivity test DS3 (without mitigation)

DS4 Bletchley Bypass removal sensitivity test DS4 (without mitigation)

DS5 Bletchley Bypass removal sensitivity test DS5 (without mitigation)

Table 5.2 Adjusted-comparison scenario pairings for which change in travel time plots have been produced

Links have been plotted according to the following criteria:

Colour of the Interpretation Notes band

Either travel time on the link is the same in both scenarios, or the change in travel time does not lead to Transparent n/a congested conditions (in which the congested travel time is at least twice the uncongested time).

Travel time in the scenario is less than in the comparison scenario (for the scenario without mitigation this is often as a result of reassignment away from The greater the decrease the thicker and Green congested links. For the scenario with mitigation this is darker the band usually as a result of mitigation scheme mitigating the impacts)

Travel time in the scenario is greater than in the The greater the increase the thicker and Red comparator. darker the band

Table 5.3 Change in travel time criteria

In addition, the percentage change in travel time is plotted adjacent to the relevant links.

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5.2 Summary of impacts

Congestion ratio and change in travel time plots have been produced for scenarios DS1 to DS5 for all time periods. Both AM and PM peak congestion ratio plots have been analysed and these findings have been presented in the main body of the report. For the change in travel time plots, only the analysis of the PM plots is presented in the main body of the report as there are relatively few changes to report for the AM peak. All remaining plots for other time periods can be found in Appendix B and C.

5.2.1 DM Scenario

For reference, the relevant DM congestion ratio plots are included below:

Figure 5.1 AM Peak DM Countywide Phase 3 Congestion Ratio Plot

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Figure 5.2 PM Peak DM Countywide Phase 3 Congestion Ratio Plot

With the committed development in the DM scenario, there is a large part of the congestion occurring along parts of the A421 and adjoining roads through the centre of Milton Keynes.

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5.2.2 DS scenario

Figure 5.3 AM Peak DS Countywide Phase 3 Congestion Ratio Plot

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Figure 5.4 PM Peak DS Countywide Phase 3 Congestion Ratio Plot

Figure 5.3 and Figure 5.4 show the congestion ratio for the Phase 3 DS model in the AM peak and PM peak periods respectively. With the committed development and Local Plan developments of that scenario, there are varying levels of congestion across the Aylesbury Vale and Milton Keynes Districts. Similar to DM, a large part of the congestion occurs along parts of the A421 and adjoining roads through to the centre of Milton Keynes.

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5.2.3 DS1 scenario

The A421 is heavily congested in parts, in both EB and WB direction. There is heavy congestion in a SB direction on Coddimoor Lane. Stoke Road also has congestion in both directions.

Figure 5.5 AM Peak DS1 Congestion Ratio Plot

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The A421 is heavily congested in parts, in both EB and WB direction. There is somecongestion in a SB direction on Coddimoor Lane. Stoke Road also has some congestion in both directions.

Figure 5.6 PM Peak DS1 Congestion Ratio Plot

The DS1 AM peak congestion ratio plot (Figure 5.5) shows little change in comparison to the Phase 3 DS plot. There continues to be heavy congestion on parts of the A421, Standing Way and the B4034. Heavy congestion is also observed on Coddimoor Lane in a southbound direction, which is where the access is for the Shenley Park development. However, despite some of the development traffic leaving the site and heading north on Coddimoor Lane, there is little congestion in a northbound direction. Likewise, the DS1 PM peak congestion ratio plot (Figure 5.5) shows little change in comparison to the Phase 3 DS plot. There continues to be congestion along Coddimoor Lane, Stoke Road and parts of the A421. The difference in travel time between this scenario and the DM is illustrated below.

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There are increases in travel time on Coddimoor Lane in a southbound direction towards the A421. Major increases in travel time can be seen on the A421 and in a segment of the Whaddon Road as it joins the A421. There is no significant change in travel time in the Milton Keynes area.

Figure 5.7 PM Peak DS1-DM Change in Travel Time Plot

There is an increase in travel time on Coddimoor Lane which is where the access is for the Shenley Park development. The increase in traffic could be a result of development traffic, which leaves the site and heads south towards the A421. There are increases in traffic on the A421 between the Bottle Dump Roundabout and the Standing Way/V1 Snelshall St/B4034 roundabout. This increase is also observed on Whaddon Road between the A412/Standing Way/Whaddon Road roundabout and Weasel Lane.

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The effects of the run 1 mitigations are shown below.

The with mitigation DS1 scenario shows a decrease in travel time on Stoke Road. There are increases in travel time with mitigation on the A421 between the Coddimoor Lane/A421 roundabout and the Bottle Dump roundabout and along Coddimoor Lane in southbound direction towards the A421.

Figure 5.8 PM Peak DS1 Mitigation Run 1-DS1 Change in Travel Time Plot

The PM peak with mitigation scenarios show the biggest change in travel time. The same changes are observed in all the DS scenarios (1-5) with mitigation scenarios. The mitigation causes decreased travel times along Stoke Road and increases along on the A421 between the Coddimoor Lane/A421 roundabout and the Bottle Dump roundabout and on Coddimoor Lane. The mitigation scenario includes the Bletchley Bypass and a new grid road in Milton Keynes which connects to the Tattenhoe Roundabout. The purpose of the new grid road is to remove some of the traffic from the A421 in Milton Keynes, immediately east of the County boundary and reduce rat-running through Whaddon. However, the presence of Bletchley Bypass increases demand flows on the A421 to the west and consequently, increases travel times. This was noted in the Phase 3 work and remains in the updated scenarios.

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5.2.4 DS2 Scenario

The A421 is heavily congested in parts in both EB and WB direction. There is heavy congestion in a SB direction on Coddimoor Lane. Stoke Road also has congestion in both directions and Bletcham Way shows congestion in a NB direction between the A5/ Bletcham Way roundabout and Bletcham Way/ Tongwell Street roundabout.

Figure 5.9 AM Peak DS2 Congestion Ratio Plot

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The A421 is heavily congested in parts in both EB and WB direction. There is some congestion in a SB direction on Coddimoor Lane. Stoke Road also has congestion in both directions and Bletcham Way shows congestion in a NB direction between the A5/ Bletcham Way roundabout and Bletcham Way/ Tongwell Street roundabout.

Figure 5.10: PM Peak DS2 Congestion Ratio Plot

DS2 shows an increase in congestion northbound between the A5/Bletcham Way roundabout and Bletcham Way/Tongwell Street roundabout within Milton Keynes in the AM peak which was not seen in the Phase 3 modelling. Across both peaks, the scenario also shows the same pattern of congestion as the DS1 and the Phase 3 DS in which there is congestion on Coddimoor Lane and on the A421 which is where both the Shenley Park and Eaton Leys developments access the network. The changes in travel time compared to the DM scenario are detailed below.

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In the DS2 PM peak, there are increases in travel time on Coddimoor Lane in a southbound direction towards the A421. Major increases in travel time can be seen on the A421 and in a segment of the Whaddon Road as it joins the A421. There is no significant change in travel time in the Milton Keynes area.

Figure 5.11 PM Peak DS2-DM Change in Travel DS2 shows the same changes in travel time as the DS1. There are increases in traffic on the A421 between the Bottle Dump roundabout and the Standingway/V1 Snelshall St/B4034 roundabout. This increase is also observed on Whaddon Road between the A421/Standing Way/Whaddon Road roundabout and Weasel Lane. The changes in travel time as a result of the mitigation measures are shown below.

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In the DS2 scenario there is a decrease in travel time on Stoke Road. Similar to the DS1 with mitigation scenario, there is a significant increase in travel time along the A421 in both directions and in addition to this there is increase in travel time on Coddimoor Lane.

Figure 5.12 PM Peak DS2 Mitigation Run 1-DS2 Change in Travel Time Plot

With the addition of mitigation run 1 in the DS2 scenario there is the same changes in travel time as that of DS1, for the same reasons.

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5.2.5 DS3 Scenario

The A421 is heavily congested in parts in both EB and WB direction. There is heavy congestion in a SB direction on Coddimoor Lane. There is also slight congestion on Whaddon Road in both directions.

Figure 5.13 AM Peak DS3 Congestion Ratio Plot

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The A421 is heavily congested in parts in both EB and WB direction. There is some congestion in a SB direction on Coddimoor Lane. There is also heavy congestion on Whaddon Road going into the Bottle D ump roundabout..

Figure 5.14: PM Peak DS3 Congestion Ratio Plot

In the AM peak, DS3 shows some additional congestion on Whaddon Road in a northbound direction that is not seen in the DS, DS1 or DS2. The additional congestion can be attributed to the additional development sites in this scenario that are not in the DS, where development traffic from these sites use Whaddon Road and Coddimoor Lane. This is expected due to the access for these sites located on the aforementioned roads. The change in travel time is illustrated below.

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The comparison of travel time from the DM to DS3 shows a similar pattern to DS1 and DS2, there are increases in travel time on Coddimoor Lane and on A421. Major increase is observed on A421 between Bottle Dump roundabout and Coddimoor Lane.

Figure 5.15 PM Peak DS3-DM Change in Travel Time Plot The DS3 scenario shows the same increases in travel time on Coddimoor Lane where the Shenley Park development access is. Further to this, in the DS3 scenario, the A421 has a slight increase in travel time on the western approach to the Bottle Dump roundabout, which could be a result of increased traffic looking to access the Salden Chase Extension development. The increased travel time on this arm is not seen in the DS, DS1 and DS2 scenarios. The increases in travel time on Whaddon Road and the A421 eastern approach to the Bottle Dump roundabout are in line with other scenarios.

The travel time changes effected by the mitigation measures are illustrated below.

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The DS3 with mitigation scenario shows the same change in travel time pattern as the DS1 and DS2. There are notable decreases in travel time on Stoke Road and increases along the A421 and Coddimoor Lane.

Figure 5.16 PM Peak DS3 Mitigation Run 1-DS3 Change in Travel Time Plot

The DS3 with mitigation shows the same changes in travel time in NE Aylesbury Vale as the DS2 and DS1.

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5.2.6 DS4 Scenario

The A421 is heavily congested in parts in both EB and WB direction. DS4 shows a decrease in congestion in a SB direction on Coddimoor Lane and in a NB direction on Stratford Road in comparison to DS1, DS2 and DS3

Figure 5.17 AM Peak DS4 Congestion Ratio Plot

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The A421 is heavily congested in parts in both EB and WB direction. SB Coddimoor Lane experiences significant congestion.

Figure 5.18 PM Peak DS4 Congestion Ratio Plot

In the DS4 scenario, the A421 is still congested in parts, despite a reduction in traffic due to the removal of the Shenley Park development. This is due to traffic to and from Eaton Leys using the A421 to travel to Buckingham. The travel time change from the DM is illustrated below.

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In the DS4 scenario, the same pattern is followed as in the DS1 and in DS2 scenarios. There is a slight increase in travel time on Coddimoor Lane and increases on Whaddon Road where it joins the A421, and following onto the A421 in an eastbound direction.

Figure 5.19 PM Peak DS4-DM Change in Travel Time Plot There are increases in traffic on the A421 between the Bottle Dump roundabout and the Standing Way/V1 Snelshall St/B4034 roundabout. The same pattern is followed on Whaddon Road between the Bottle Dump roundabout and Weasel Lane. There is also a slight increase in travel time on Coddimoor Lane. A decrease in travel time is observed on Stoke Road.

The effects of the mitigation measures on travel time are illustrated below.

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Like DS1-3 with mitigation scenarios, the DS4 with mitigation scenario shows a significant increase in travel time along the A421 and on Coddimoor Lane. There are also decreases along Stoke Road and Warren Road.

Figure 5.20 PM Peak DS4 Mitigation Run 1-DS4 Change in Travel Time Plot

The impacts of the mitigation measures in the DS4 scenario are similar as for the DS1-DS3 scenarios, for similar reasons.

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5.2.7 DS5 Scenario

The A421 is heavily congested in parts in both EB and WB direction and on roads joining it. Similar to DS4, DS5 shows a decrease in congestion in a SB direction on Coddimoor Lane and in NB direction on Stratford Road in comparison to DS1, DS2 and DS3.

Figure 5.21 AM Peak DS5 Congestion Ratio Plot

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Figure 5.22 PM Peak DS5 Congestion Ratio Plot

Figure 5.21 and Figure 5.22 generally shows where there is slight to heavy congestion which can be linked to the Salden Chase Extension development. Both origin and destination traffic for the development site use the A421 to travel to Buckingham and also Standing Way for travel to Milton Keynes. The effects on travel time in comparison to the DM scenario are illustrated below.

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The comparison of travel time between the DM and DS5 shows a similar pattern to DS3 scenario; there are increases in travel time on Coddimoor Lane and on A421. Slight increases on A421 between the Bottle Dump roundabout and Coddimoor Lane.

Figure 5.23 PM Peak DS5-DM Change in Travel Time Plot In DS5, the same pattern as in DS3 is followed with the travel time increases on the western approach to the Bottle Dump roundabout. There are increases in traffic on the A421 between the Bottle Dump roundabout and the Standing Way/V1 Snelshall St/B4034 roundabout. The same pattern is followed on Whaddon Road between the Bottle Dump roundabout and Weasel Lane. Note that Coddimoor Lane shows relatively less change in travel time in this scenario, compared to all the previous scenarios.

The effect on travel time of the mitigation scenarios is illustrated below:

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The DS5 with Mitigation is very similar to that of DS4 and other DS scenarios with Mitigation. There is a slight decrease in travel times along Stoke Road.

Figure 5.24 PM Peak DS5 Mitigation Run 1-DS5 Change in Travel Time Plot

As with scenarios DS1-DS4, the changes in travel time resulting from the mitigation scenarios show increases on the A421 due to additional traffic using the road via the new infrastructure introduced as part of the mitigation package.

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5.3 Bletchley Bypass Removal Sensitivity Test A further assessment of the impact of the Bletchley Bypass removal has been undertaken. Congestion ratio plots have been produced for scenarios DS1 to DS5 for all time periods for this assessment. Both AM and PM peak plots have been presented below. The plots for the other time periods can be found in Appendix A and B.

5.3.1 DS Scenario Bletchley Bypass Removal

Figure 5.25 AM Peak DS Bletchley Bypass Removal Congestion Ratio Plot

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Figure 5.26 PM Peak DS Bletchley Bypass Removal Congestion Ratio Plot

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5.3.2 DS1 Scenario Bletchley Bypass Removal

Figure 5.27 AM Peak DS1 Bletchley Bypass Removal Congestion Ratio Plot

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Figure 5.28 PM Peak DS1 Bletchley Bypass Removal Congestion Ratio Plot

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5.3.3 DS2 Scenario Bletchley Bypass Removal

Figure 5.29 AM Peak DS2 Bletchley Bypass Removal Congestion Ratio Plot

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Figure 5.30 PM Peak DS2 Bletchley Bypass Removal Congestion Ratio Plot

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5.3.4 DS3 Scenario Bletchley Bypass Removal

Figure 5.31 AM Peak DS3 Bletchley Bypass Removal Congestion Ratio Plot

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Figure 5.32 PM Peak DS3 Bletchley Bypass Removal Congestion Ratio Plot

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5.3.5 DS4 Scenario Bletchley Bypass Removal

Figure 5.33 AM Peak DS4 Bletchley Bypass Removal Congestion Ratio Plot

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Figure 5.34 PM Peak DS4 Bletchley Bypass Removal Congestion Ratio Plot

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5.3.6 DS5 Scenario Bletchley Bypass Removal

Figure 5.35 AM Peak DS5 Bletchley Bypass Removal Congestion Ratio Plot

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Figure 5.36 PM Peak DS5 Bletchley Bypass Removal Congestion Ratio Plot

The results of the removal of the Bletchley Bypass show that there is an increase in congestion on roads in close proximity to where the proposed Bypass would join the existing infrastructure, such as Stoke Road.

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6. Summary and conclusion

6.1 Summary of results

Table 6.2 summarises the results of the modelling for each scenario. It is important to note that the table highlights the extent to which the Local Plan development impacts an area in terms of travel time changes, as well as the extent to which mitigation has been successful at reducing the impacts observed in the DS scenario across the geographic area. A RAG (red, amber or green) rating has been applied to each area based on a purely qualitative assessment of the overall impact of the VALP DS scenario in terms of increased travel time; red represents a significant impact, amber a moderate impact and green a slight impact in comparison to the DM. A second RAG rating has also been applied based on a qualitative assessment of the overall improvement, if any, the DS with mitigation scenario provides.

Table 6.1 outlines a broad definition of each qualitative category. This rating is based only on the outputs produced as part of this phase of modelling.

RAG Description rating

Overall significant impact in terms of travel time increases on a number of key routes through the area compared with DM (without mitigation) and DS (with mitigation) Overall moderate impact in terms of travel time increases on a number of key routes through the area compared with DM (without mitigation) and DS (with mitigation)

Overall slight impact in terms of travel time increases on a number of key routes through the area compared with DM (without mitigation) and DS (with mitigation)

Table 6.1 RAG rating description

Scenario Model Areas DS RAG With Comments rating Mitigation RAG rating

DS1 NE Aylesbury The roads impacted by the local plan in NE Vale District Aylesbury in the DS1 scenario are the A421, Coddimoor Lane and Whaddon road. These have significant increases in travel times. However, Stoke Road is impacted positively observing a decrease in travel time in the DS1 scenario. The run 1 mitigation adds to travel times, due to increased demand on the A421 as a result of new infrastructure. DS2 NE Aylesbury DS2 follows a similar pattern to DS1. There is Vale District further significant increases in travel on Whaddon Road where it joins the A421. The with mitigation scenario shows a decrease in travel time along Stoke Road, however there is an increase in travel time on the A421 between Standing Way/Whaddon Road roundabout and Coddimoor Lane which is not seen in the DS1 with mitigation.

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Scenario Model Areas DS RAG With Comments rating Mitigation RAG rating

DS3 NE Aylesbury There are travel time increases in both the AM and Vale District PM peak, especially significant on the A421 in the PM. Coddimoor Lane observes only slight increase in travel time and the A421 has a significant increase in travel time on the A421 which is greater than that of DS2. The with mitigation shows the same CTT as DS1 and DS2. DS4 NE Aylesbury In the DS4 scenario there is less increase in travel Vale District time than in DS1-3, albeit the increases are still significant. The majority of impact falls on the Milton Keynes side of the district boundary. There is a significant increase in travel on Whaddon Road where in joins the A421. In the with mitigation scenario there are increases along the A421 as with the other mitigation scenarios, increases in travel time of Coddimoor Lane but decreases on Stoke Road. DS5 NE Aylesbury DS5 shows similar increases in travel times as all Vale District other scenarios. However, the impacts on Coddimor Lane are not quite as severe. The ‘with mitigation’ scenario shows a greater increase in travel time along the A421, however there is a significant decrease in travel time on Stoke Road.

Table 6.2 Impact Summary Table

6.2 Summary of individual development impacts

Like section 6.1, a RAG rating has been applied to qualitatively assess the impact on traffic each of the three developments. To assess the individual impact of each development, appropriate ‘with development’ and ‘without development’ DS and DS mitigation scenarios were chosen for comparison. Table 6.3 outlines a broad description of each qualitative rating category, while Table 6.4 summarises the individual impact of each development.

RAG rating Description

Overall significant impact in terms of travel time increases on a number of key routes in the vicinity of the development compared with the DS and DS mitigation scenarios without the development Overall moderate impact in terms of travel time increases on a number of key routes in the vicinity of the development compared with the DS and DS mitigation scenarios without the development

Overall slight impact in terms of travel time increases on a number of key routes in the vicinity of the development compared with the DS and DS mitigation scenarios without the development

Table 6.3: RAG rating description

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Bletchley DS RAG With Mitigation Development Comparison Bypass Comments rating RAG rating Removal

DS2 (with There are moderate increases in development) vs journey times along the A421 Shenley Park DS4 (without corridor when the development development) is included.

DS3 (with There are moderate increases in Salden development) vs journey times along the A421 Chase DS (without corridor when the development Extension development) is included.

DS2 (with The development has a slight development) vs impact on journey times along Eaton Leys DS (without the A421 corridor and A5 development) corridor.

Table 6.4: Individual development impacts summary table

Reviewing the extracted plots and overall traffic patterns in the models shows that of the developments that were assessed, Eaton Leys has the least impact on traffic in the NE of the Aylesbury Vale district.

6.3 Conclusions

The Countywide Model has been used to indicate how three additional Local Plan developments in Aylesbury Vale near to Milton Keynes impact on the local highway network. The results show that there are likely to be no further negative impacts in terms of increased journey times and congestion in the area, than was observed as in the previous Phase 3 work.

The model has also been used to indicate the extent to which proposed transport improvement measures are likely to mitigate the impacts of the local plan development. The extent to which the mitigation measures have been successful varies, with general increases along the A421, due to increased demand flow facilitated by the Bletchley Bypass and the new grid road. There is however a general decrease in travel time along Stoke Road.

It should be noted that when assessing impacts and the extent to which they are mitigated, there is no universal definition of how to define an impact, and what impacts are considered “acceptable” and “unacceptable”. It should also be noted that given the strategic nature of the Countywide model the impacts identified are appropriate for a qualitative assessment. The model has been used to provide a relatively high level indication of the potential impacts of the local plan and proposed mitigations, commensurate with the requirements of local plan evidence base. A RAG analysis of the potential impacts has been provided for NE Aylesbury Vale District, which is appropriate given the nature of the strategic model, but the quantification of the scale of impact based on the model (beyond the terms slight, moderate and significant) should be avoided.

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Appendix A. Phase 3 Methodology and Assumptions (taken from the Phase 3 Technical Note, Section 2)

A.1.1 Modelling methodology

Overview

This section sets out the modelling methodology adopted to develop the phase three forecast scenarios. Three forecast scenarios were originally developed during the first and second phases of the work. For phase three this has been reduced to a DM (carried over from phase two) and a DS scenario, which reflects the revised local plan development scenario and omits the new settlement at both Haddenham and Winslow.

Forecast model updates

Revised forecast scenarios

The land use assumptions for the DM scenario remain unchanged from the previous phases of work, however a number of revisions have been made to the development growth assumptions in the DS forecast scenarios. Further details of these changes are provided in section A.1.3 of this technical note.

The methodology for producing the revised forecast matrices is for the most part consistent with phase one and two, as outlined in their respective modelling reports Error! Bookmark not defined.Error! Bookmark not defined. . However, the DS scenario will now be comprised of the revised phase three local plan development quantum provided by the four districts. In addition, the phase 2 trip distributions used for the DS local plan development sites have been reviewed, and in some cases revised, where a more suitable donor zone is available.

For the previous phases of work two separate DS scenarios were developed. These scenarios included the same mix of local plan development but the location of a new settlement near Haddenham, included in the DS1 scenario, was instead moved to Winslow in the DS2 scenario. For phase three both these sites have been removed, and therefore only a single DS land use scenario is required to be developed.

Crossrail and East West Rail (EWR)

As with phase two, the impacts of Crossrail and East West Rail (EWR) have been modelled in the phase three DS forecast scenario in the form of a reduction in car journeys (to represent a mode shift from car to rail) in impacted areas. The extent of the reduction in car journeys has been derived using the following assumptions: • Only car journeys which start or end within 1,500m of a Crossrail or EWR station are considered (for stations that fall within the London zones, all car journeys have been considered). • 10% of these journeys will switch from car to rail in relation to EWR. • 35% of these journeys will switch from car to rail in relation to Crossrail.

The assumed percentage reductions and radii were calibrated such that the outturn reduction in car trips approximated the reductions calculated by separate third party modelling of those schemes. This was to ensure that the modelling assumptions/trip impacts were consistent across the different modelling exercises for business case development for these national strategic infrastructure schemes. This modelling data was provided by Transport for London in regards to Crossrail and Atkins in relation to EWR.

A.1.2 Modelling the mitigation options

For phase three two separate mitigation scenarios have been developed known as run 1 and run 2, which include a different combination of mitigation options, but the same land use assumptions as with the DS

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scenario. Section A.1.4 of this note provides further detail of the sifting process and options identified for each run. The following subsections summarise the methodology adopted to model the mitigation options in the DS forecast network.

Highway schemes

A number of highway schemes have been added to the DS scenario in consultation with BCC and the districts. The majority of these schemes were already modelled for phase two, and as a result the network coding has been carried over for this phase of work. However, several of the schemes included where not previously modelled, and in these cases detailed descriptions or concept designs have been used instead.

Where information has been unavailable for a specific scheme or if a scheme is in the early stages of conception, sensible assumptions have been made, in consultation with BCC, to ensure each mitigation scheme is represented as accurately as possible within the model.

Public/ sustainable transport schemes

To account for the public transport and sustainable transport schemes in the model, a similar methodology has been adopted as with phase two, where a reduction in car journeys has been calculated for impacted areas. Several such schemes have been considered as part of the mitigation options. These include a number of bus corridor schemes, Wycombe Bus Station Upgrade, improvements to Aylesbury Town Centre, and Grand Union Triangle improvements (further detail of all these schemes is provided in Table 6-I).

The extent of the reduction in car journeys has been based on evidence from the sustainable travel towns’ evidence base 4, as agreed with BCC. The schemes in that evidence base are of a similar nature to the proposed mitigation measures. To calculate the reduction in car journeys the following assumptions have been used: • The location and extent of the schemes has been defined using the provided concept drawings. • Only car journeys which start and end within 1,000m of a public transport scheme are considered (for the Aylesbury Town Centre improvements car journeys which start or end within 1,000m of the scheme have been considered, to account for the likely wider impact that may be experienced). • A total of 3% of all car journeys in the 2033 forecast which met the above criteria were assumed to switch from car to sustainable transport. This is in-line with the percentage reduction observed in the sustainable travel town’s evidence base.

A.1.3 Development scenarios

Overview

Development summary

The DM scenario remains unchanged from the previous phase of work; however, at the request of BCC and the districts the following amendments have been made to the DS forecast scenario for the four districts of Buckinghamshire.

4 Department for Transport. 2010. The effects of Smarter Choice Programmes in the Sustainable Travel Towns: full report. https://www.gov.uk/government/publications/the-effects-of-smarter-choice-programmes-in-the-sustainable-travel-towns-full-report.

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• Aylesbury Vale – A reduction in overall HELAA housing growth but the same level of job growth across the district.

• Chiltern and South Bucks – An increase in overall job growth to reflect the preferred greenbelt option, but the same level of housing growth across the two districts.

• Wycombe – An increase in both Local Plan housing and job growth across the district.

Table 6-E provides a summary of the DM land use assumptions and the absolute differences between the phase two and phase three employment and housing figures for the DS scenario. Further details of the total housing and employment figures can be found in sections 0 and 0.

Future scenario (2033) Summary details

• Unchanged from phase two and comprised of: • 9,416 houses and 24,265 jobs in Aylesbury Vale; • 1,278 houses and 0 jobs in Chiltern; Do Minimum (DM) ‘No development’ • 1,297 houses and 1,619 jobs in South Bucks; and • 2,180 houses and 6,011 jobs in Wycombe. • Total: 14,171 houses and 31,895 jobs.

• As phase two but; • A reduction of 2,143 houses in Aylesbury Vale; • An additional 522 jobs in Chiltern; Do Something (DS) • An additional 2199 jobs in South Bucks; and • An additional 1,360 houses and 1,070 jobs in Wycombe district. • Total: 52, 373 houses and 48,624 jobs.

Table 6-E Revised forecast scenarios

Compared with phase two, there is a reduction of 783 houses and an increase of 3,791 jobs in the DS forecast scenarios, across the county. The reductions in housing in Aylesbury Vale (compared with the phase two work) offsets the increase observed in Wycombe. This leads to an overall housing reduction from the phase two figures, when compared across the county as a whole. Chiltern, South Bucks and Wycombe all experience an overall increase in jobs, leading to a net gain at the county level compared with phase two.

Figure 6-A and Figure 6-B illustrates the phase three DS housing and job growth by model zone, respectively.

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Figure 6-A DS housing growth (including DM) by model zone

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Figure 6-B DS jobs growth (including DM) by model zone

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Do Something

Within the county the DS scenario contains the DM land use quantum plus the revised local plan development scenario for phase three. For all areas outside of Buckinghamshire, growth in employment and housing is consistent with NTEM levels of growth. Table 6-F provides a summary of the DS scenario.

Location Totals

Aylesbury Vale District • DM commitment plus 20,207 houses and 6,069 jobs

Chiltern District • DM commitment plus 3,847 houses and 522 jobs

South Bucks District • DM commitment plus 4,324 houses and 6,578 jobs

Wycombe District • DM commitment plus 9,824 houses and 3,560 jobs

Outside of Buckinghamshire • Capped to NTEM growth levels

Total within Buckinghamshire • DM commitment plus 38,202 houses and 16,728 jobs

Table 6-F Do Something 3 growth

Revised forecast traffic growth Table 6-G provides a summary of the changes in total trips for cars for each district in DS scenario between phase two and phase three as a percentage.

District AM peak trip change IP trip change PM peak trip change

Origin Destination Origin Destination Origin Destination

Aylesbury Vale -3% -2% -4% -5% -2% -3%

Chiltern 0% 1% 0% 0% 1% 0%

South Bucks 2% 5% 4% 4% 5% 3% Wycombe 1% 1% 1% 1% 2% 1%

Table 6-G Change in Car total trip ends from phase two DS scenario to the phase 3 DS scenario

As a result of the revised land use information and changes to trip generation included in phase two, the total trip generation has fallen in Aylesbury Vale but increased in the other three districts, compared with the previous phase of work. This reflects the land use changes described in Table 6-E.

Comparison with NTEM

Table 6-H provides a summary of the total household and job growth for the 2033 forecast scenario. The table also includes NTEM growth figures for the period 2013 to 2033, from version 6.2 of the dataset, for comparative purposes.

Consistency with NTEM growth figures is a requirement for all WebTAG compliant models to be used for major scheme business cases. However, because the purpose of this modelling is for a local plan assessment rather than a business case, it is not necessary to constrain growth to NTEM. Indeed, because the local plan growth is generally in excess of NTEM levels (particularly in South Bucks), it was decided that capping to NTEM growth would not be appropriate.

Nonetheless, a comparison of the model against NTEM is useful as it helps to identify the scale of difference between NTEM and the local plan assumptions, and thereby understand how the districts’ local plan growth differs from the levels of growth mandated by the Department for Transport for use in transport scheme business cases. As can be seen from the below table, the level of growth in houses and jobs in the DS forecast

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scenario is higher than NTEM growth levels for the same period overall. However, NTEM provides a higher number of households for Aylesbury Vale, and higher number of jobs for Chiltern and Wycombe than the DS growth figures. The amount of jobs growth assumed as a whole for the DS scenario represents a ‘worst case’ for traffic impacts in that they represent the maximum possible amount of anticipated employment growth

NTEM DM DS District HH Jobs HH Jobs HH Jobs

Aylesbury Vale 32,243 11,172 9,416 24,265 29,623 30,334 Chiltern 4,549 3,297 1,278 0 5,125 522 South Bucks 924 2,497 1,297 1,619 5,621 8,197 Wycombe 7,289 14,683 2,180 6,011 12,004 9,571 Total 45,004 31,649 14,171 31,895 52,373 48,624

Table 6-H 2033 modelled scenario growth and NTEM growth

A.1.4 Mitigation options

Overview

This section describes the development of the mitigation scenarios and the selection of the schemes tested. Table 6-I presents the final mitigation options included in each run of the mitigation model.

Option generation

As part of the phase two work, a long list of schemes was put together by BCC in collaboration with the districts. This included a variety of highway improvements (upgraded roads, junction improvements, relief roads etc.) and an assortment of public transport schemes with the aim of encouraging a mode shift from car to sustainable transport (upgraded bus and rail facilities, improvements to the cycling network, public transport initiatives etc.).

The options were designed to address strategic issues identified in the phase two modelling, as well as concerns of a more localised nature, tackling areas and facilities that could be enhanced and developed in order to reduce congestion and delay arising from the additional housing and employment developments across the county.

In addition, several new schemes were also added to the long list for the phase three work which weren’t considered for phase two, as at that stage there was not enough information available to model the schemes. These schemes include Iver Relief Road and Queensway Link.

Option sifting

A workshop was held with BCC and the districts during phase two to sift schemes from the long list. A number of these schemes were aspirational in nature with minimal scheme development or design, and as a result were excluded from the final short list of mitigations. The schemes that were shortlisted were then assessed as part of the phase two work to understand the effect that they may have in regards to alleviating the impacts of the proposed housing and employment sites. It should be noted that a number of these schemes are still at the concept stage and would require significant additional work to develop into deliverable schemes.

The list of mitigation options previously shortlisted for the Countywide Local Plan forecasting Phase 2 work was carried over for this phase of the work. However, in some cases mitigation measures were not included due to changes in the development scenario e.g. mitigation measures linked to the new settlements at Haddenham or Winslow were excluded as these proposals were no longer part of the development scenario for Phase 3. In a

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few cases new mitigation measures were added, although these, on the whole, reflected the results of more detailed Local Plan modelling undertaken for Chiltern and South Bucks and for Wycombe District Councils.

For phase three, BCC requested that two separate mitigation scenarios be developed, referred to as run 1 and run 2. The mitigation measures vary between each of the runs in Aylesbury Vale and Chiltern and South Bucks districts to enable a comparison between the different effects of combinations of mitigation measures.

The mitigation schemes included for phase two (and generated for phase three) have been reviewed in collaboration with BCC and the districts, and a number of the schemes have been selected to be tested in run 1 and run 2 of the mitigation scenarios.

Options for appraisal

Table 6-I outlines each mitigation option taken forward for appraisal in each mitigation scenario after the sifting process was completed. Table 6-J summarises the main differences between the two mitigation scenarios by district.

District Scheme name Scheme description Run 1 Run 2

This scheme consists of a new east-west single North-East Link Road carriageway link road to the north-east of Aylesbury, No Yes (NELR) between the A413 and A418.

The southern section of the Eastern Link Road will complete a new north-south, single carriageway road between the A418 Aylesbury Road and A41 Aston Eastern Link Road (South) Clinton Road, to the east of Aylesbury. Yes Yes The scheme will provide access to the Woodlands Development, and will include an upgraded A41 Roundabout.

The Southern Link Road between the A41 Aston Clinton Road and A413 Wendover Road is already Southern Link Road included in the without mitigation scenarios. However Yes Yes (upgrade) as a mitigation option, this scheme was upgraded to dual carriageway standard, and includes a new roundabout and left-in left-out access junction. Aylesbury This scheme seeks to extend the planned Stoke Vale Stoke Mandeville Bypass Mandeville bypass (A4010 realignment) with a new Yes Yes Extension single carriageway road to meet the Southern Link Road at the A413 Wendover Road.

The South Western Link Road scheme will connect the A418 Oxford Road to the planned realigned A4010 (Stoke Mandeville bypass) with a new single South Western Link Road No Yes carriageway road. It will include a new roundabout on the new Stoke Mandeville bypass and a new entry to the A418 roundabout.

This scheme consists of a new NW-SE single carriageway link road to the west of Aylesbury linking Western Link Road the A418 and A41 at Fleet Marston, west of the A41 No Yes Berryfields junction. This scheme will finish a complete orbital of Aylesbury.

Signal timing optimisation has been carried out to A41 Berryfields Junction No Yes better accommodate demand at this junction.

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District Scheme name Scheme description Run 1 Run 2

The scheme tests a reduction in capacity on the Willows Capacity Willows to encourage traffic to use the A41 at No Yes Reduction Berryfields.

The scheme includes implementing bus priority measures (e.g. bus lanes and priority at traffic lights). A41 Bicester Road PPTC The improvement will aim to significantly improve Yes Yes journey time reliability and increase the public transport mode share.

The scheme includes implementing bus priority measures (e.g. bus lanes and priority at traffic lights). A41 Tring Road PPTC The improvement will aim to significantly improve Yes Yes Improvements journey time reliability and increase the public transport mode share.

Stoke Road Signalised Signal timing optimisation has been carried out to Yes Yes Junction better accommodate demand at this junction.

Traffic calming between Traffic calming on Prebendal Avenue to reduce rat- Yes Yes A418 and Stoke Mandeville running between A418 and Stoke Road.

This scheme seeks to improve the approach to the Horse and Jockey junction by dualling the route and A413 Buckingham Road optimising the signals at the junction to reduce the No Yes Improvements level of queuing on the A413 Buckingham Road. The junction with Oliffe Way has also been upgraded to a priority junction.

Aylesbury Town Centre This improvement aims to increase safety and Pedestrian Network enhance the public realm in Aylesbury Town Centre. Yes Yes Improvements

This scheme is designed to provide cost-effective off- road walking and cycling routes in an area of major growth. The project includes improving existing Grand Union Triangle Yes Yes towpaths, the upgrade of a public footpath to a bridleway and then implementation of connecting routes and some small scale improvements.

This scheme includes a new link road between the Buckingham Western Link No Yes A421 and A422.

Three separate mitigations have been included as part of the transport strategy. • Route downgrade between High St and West St to reduce traffic flows through the Buckingham Area town centre No Yes Transport Strategy • Additional left turn slip at the A422 Stratford Rd/ A413 roundabout • Route upgrade on the A421 and A413 to dual – 2 lane standard

A421 Roundabout Capacity improvements at the London Rd/ A421 Rbt Yes No Capacity Improvements and Gawcott Rd/ A421 Rbt to increase capacity.

A421 Corridor Capacity A421 route upgrade to dual-2 lane standard between No Yes Improvements Buckingham and Milton Keynes.

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District Scheme name Scheme description Run 1 Run 2

This scheme will implement a new grid road to the New Grid Road in Milton A421 adjacent to the V1 to discourage rat running Yes Yes Keynes through Whaddon.

This scheme consists of a new single-carriageway Bletchley By-Pass road joining the A421 and A4146 South West of Yes No Bletchley. This package includes two separate improvements. The first is a road to the west of the existing A4010. Alignment option 11b has been included in the model Princes Risborough in this case. Yes Yes Infrastructure Package The second includes a number of improvements to the A4010 including traffic calming and the introduction of a number mini-roundabouts.

This scheme involves upgrading the school drop off Daws Hill - Sports Centre area and a new public transport route with improved Yes Yes Public Transport Bus Link frequencies.

Heath End Road / Abbey This scheme includes relocating and replacing the Barn Lane Junction Yes Yes current junction with a roundabout to the west. Improvements

This project will support the development of an integrated package of measures to improve junction A404/A4155 Westhorpe capacity at the Westhorpe junction. In this case it Yes Yes junction Improvements includes measures to improve capacity on the northbound exit slips of the A404 only.

Wycombe This includes a number of separate mitigations to A40 corridor improvement improve traffic conditions on the A40 through High Yes Yes Wycombe (excludes Genoa Link).

This scheme includes a new link road to the east of Gomm Valley Spine Road High Wycombe, associated with the Gomm Valley Yes Yes development.

The scheme includes implementing bus priority measures (e.g. bus lanes and priority at traffic lights). PPTC: Desborough The improvement will aim to improve journey time Yes Yes Avenue / A404 Marlow Hill reliability and increase the public transport mode share.

Wycombe Bus Station Improvements to Wycombe Bus Station to improve Yes Yes Upgrade the service provided.

This scheme involves the introduction of a single Holland Farm Spine Road carriageway spine road through the Holland Farm Yes Yes development from Hedsor Road to Princes Road.

Adds a new link road to the north-east of the New Link at Queensway Hazelmere Crossroads to alleviate congestion at the Yes Yes junction.

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District Scheme name Scheme description Run 1 Run 2

Gore Hill Roundabout Capacity improvements at the junction to reducing No Yes Improvements queueing.

A series of new signalised junctions through A416 congestion Chesham to improve signal coordination through the No Yes management corridor town centre.

This scheme includes signal optimisation, an Berry Hill Junction additional eastbound traffic lane on Bath Road and a No Yes Improvements right turn ban into Berry Hill.

This scheme aims to improve the geometry and lines A412 Improvement of sight at the A412 Five Points roundabout through Yes Yes widening and partly signalising the junction.

Chiltern This scheme includes traffic calming on several roads and South in Beaconsfield including Wattleton Road, Burkes Beaconsfield Transport Bucks Lane, Holtspur Top Lane, Gregories Road and Yes Yes Strategy Candlemass Lane. It also includes a ban of right turns at the A40/ Broad Lane junction.

A412/ Bangors Road North Capacity improvements including widening to two No Yes Capacity Improvements lanes to reduce queuing on the northbound approach.

This scheme moves the site access for the Land North of Denham Roundabout from Priory Close to Land North of Denham Rbt Yes Yes Denham Court Drive to alleviate congestion at Denham Rbt.

This scheme adds a new relief road between Thorney Iver Relief Road Lane South to Mansion Lane to provide an alternate No Yes route for HGVs currently using Iver High Street.

Table 6-I List of options to include in the DS with mitigation forecast scenarios

TN02 63 NE Bucks Local Plan Tests -Technical Report

District Run 1 Run 2

Aylesbury Aylesbury Run1 includes the majority of schemes with Run 2 includes the complete circle of link roads the exception of the link roads to the north and as well as the improvements at the A41 west, improvements at the A41 Berryfields Berryfields Junction and on the A413. junction and on the A413. Buckingham/ Milton Keynes Aylesbury Vale Buckingham/ Milton Keynes Run 2 includes the majority of mitigation Run 1 does not include any schemes in schemes in Buckingham but excludes the Buckingham except the A421 roundabout Bletchley Bypass and A421 roundabout improvements but includes the Bletchley improvements and instead includes dualling the Bypass. A421 between Buckingham and Milton Keynes instead.

All mitigations schemes are included in both All mitigations schemes are included in both Wycombe runs. runs.

Run 1 of the mitigation includes the 5 Point Run 2 includes all schemes from run 1 plus the Roundabout improvements, Beaconsfield Iver Relief Road, Bangors Road North Transport Strategy and the relocation of the improvements, Chesham congestion Chiltern and site access for the Land North of Denham management corridor, Berry Hill junction South Bucks Roundabout. improvements and the Gore Hill Roundabout improvements.

Table 6-J Summary of mitigation schemes included in each mitigation forecast scenario

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Appendix B. Congestion Ratio Plots

B.1 DM Congestion Ratio Plots

Congestion Ratio DM AM