Glos Transport Plan A40 2003
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Gloucestershire Local Transport Plan Annual Progress Report 2003 Appendix D A40 Improvements and Park and Ride Contents 1 INTRODUCTION 1 2 A40/A48 HIGHNAM WOOD 4 3 A40/B4215 LINTON 5 4 A40/A417 OVER 8 5 A40/A38 LONGFORD 11 6 A40/A417 ELMBRIDGE COURT 14 7 SUMMARY AND SCHEME COSTS 18 8PARK AND RIDE PROVISION 19 9 CONCLUSION 20 1 Introduction The A40 is a strategic east-west route across the County. As well as providing for national and regional movements, it is a major corridor through the Central Severn Vale (CSV). The A40 provides the CSV’s main link to the motorway network and it forms the northern bypass to Gloucester and 2 important radials within Cheltenham. It also provides the only access to Gloucester from a large area to the west of the Severn. As a consequence the A40, particularly on the section around and to the west of Gloucester, is often congested. The A40 is managed by the Highways Agency, but detrunking orders have been issued for the entire length of the route throughout the county along with the A48. The County Council has lodged an objection to the order on the basis of capacity and safety issues along the route with particular concern around the Gloucester area and on the basis of the need to develop an integrated approach to resolving the problem. The Council has undertaken an initial assessment of the A40 from Highnam Roundabout to Elmbridge Court Roundabout. This study established a £4million package of measures for five junctions (Highnam, Linton (B4215), Over, Longford and Elmbridge Court) to achieve an increase in capacity and to pave the way for the introduction of two park and ride sites. The details of this study are included in this appendix. These measures would provide a considerable reduction in journey time and thereby assist the Government in its aim of reducing congestion on inter urban routes, bringing associated economic and environmental benefits to the area. These measures should resolve most of the County’s concerns regarding detrunking. However, it is recognised that they are only the first step in the implementation of an integrated package of measures to provide a longer term solution and to avoid the extra capacity being filled up. For these reasons a more detailed study of the A40, including the Cheltenham section, has now been commissioned. This will build on the recommendations from the first study and will look at the introduction of 2 park and ride sites for Gloucester and 1 new and 1 expanded site for Cheltenham along with bus priorities and other traffic management measures. This work will include the CSV Saturn model presently being built in a partnership between the County Council and the Highways Agency and other studies underway as part of the development of the County’s second Local Transport Plan. Halcrow Study In October 2000, Halcrow Fox was commissioned jointly by Gloucestershire County Council, Gloucester City Council and Tewkesbury Borough Council to develop a Park and Ride strategy for the city of Gloucester. The strategy has the following objectives: ■ To identify the most effective combination of Park and Ride sites to serve Gloucester. ■ To identify improvements to the east-west A40 strategic route to the north of Gloucester. ■ To identify in broad terms where complementary public transport measures will be required to support Park and Ride and give greater priority to public transport. This report presents the results of the A40 route assessment element of the study, identified in (b) above. The results of the other elements are presented separately. The following chapters describe the assessment of each junction along the section of the A40 assessed, while the final chapter gives details of the cost estimates for improvements proposed at these junctions. A40 Route Assessment As part of the Park and Ride strategy, the study brief required an investigation into the existing congestion and delay experienced on the A40 to the north of Gloucester, between its junctions with the A48 at Highnam Wood and the A417 at Elmbridge Court, as shown in Figure 1.1. 1 This investigation was to focus in particular on the assessment of problems and potential solutions at the following junctions: ■ A40/A48 roundabout, Highnam Wood; ■ A40/B4215 junction, Linton; ■ A40/A417 roundabout, Over; ■ A40/A38 roundabout, Longford; ■ A40/A417 signalised roundabout, Elmbridge Court. The capacity of each of these junctions was assessed using appropriate computer software. ARCADY/5 was used to examine the roundabouts at Highnam Wood, Over and Longford. The part- time traffic signals at the A40/B4215 junction do not operate during the morning peak period, and so this junction was assessed using both the PICADY/4 and LINSIG computer programs. The signalised roundabout at Elmbridge Court was studied using TRANSYT/11. In undertaking these assessments, use was made of existing recent junction count data where possible. New data were required, however, at the Over and Elmbridge Court junctions, which were carried out in November 2000 using video camera surveys. Table 1.1 lists the surveys used in the junction assessments. Table 1.1 - A40 Junction Surveys Location Date of Survey A40 / A48 Highnam Wood 5 July, 2000 A40 / B4215 Linton 4 April, 2000 A40 / A417 Over 21 November, 2000 A40 / A38 Longford 15 September, 1998 A40 / A417 Elmbridge Court 21 November, 2000 In addition to the junction surveys, journey time surveys were undertaken over the length of the A40 between Elmbridge Court and Highnam Wood during different time periods on 29 November 2000. Whilst this information is not sufficient to derive statistically accurate data on journey times, it does provide a valuable aid in determining when and where congestion is currently occurring on this part of the route. In each case, the parameters used in the junction models were adjusted to ensure that the model gave a reasonable representation of observed congestion and queuing. The models were then used to consider possible improvement schemes that might be introduced in order to reduce congestion. 2 Figure 1.1: A40 Route Study and Park and Ride sites Innsworth Elmbridge Court Linton Brockworth Junction Park and Ride 3 2 A40/A48 Highnam Wood Existing Situation This junction is located at the western end of the section of A40 studied, where the A48 trunk route from Lydney and Chepstow joins the A40 trunk route from Ross-on-Wye. It takes the form of a three- arm roundabout with an inscribed circle diameter of 75 metres, and all of the approaches to the junction are well aligned. On the east side of the junction, the A40 route from Gloucester is a dual carriageway, with a two-lane approach. The exit from the roundabout towards Gloucester also has provision for two lanes, but eastbound traffic is obliged to merge into a single lane within a short distance because of the layout of the adjacent junction with the B4215 at Linton. The approaches on the A40 (west) and the A48 are both single carriageways. The junction was modelled using the ARCADY/5 computer program. The survey results indicate that there are very low flows turning between the A40 (west) and the A48 in both peak hours, so that the great majority of traffic on both approaches turns towards Gloucester. The effect of this is that, at the entry of both arms onto the roundabout, lane usage is very unequal, so that nearly all traffic on both of these arms uses a single lane to enter the roundabout. The entry geometry entered into the ARCADY model on these arms was therefore artificially adjusted to take account of this. The results from the ARCADY assessment are shown in Table 2.1. This shows that in the evening peak period, the junction has a significant amount of spare capacity, with minimal queuing, and that the effect of the unequal lane usage is therefore marginal. In the morning peak period, however, the unequal lane usage on the A40 (west) leads to the approach becoming over-saturated, with significant queuing. Table 2.1 - A40/A48: Arcady Results, Existing Layout A40 (Gloucester) A48 (Chepstow) A40 (Ross) Max. RFC Max. Queue Max. RFC Max. Queue Max. RFC Max. Queue AM Peak 0.37 1 0.83 5 1.24 91 PM Peak 0.73 3 0.38 1 0.47 1 AM Peak (corrected) 0.37 1 1.51 229 1.37 183 Note: RFC = Ratio of Flow to Capacity Site observations, however, show that severe congestion occurs in the morning peak period on both the A40 (west) and A48 approaches, which can extend for over 1km. This queuing is, however, caused by problems generated at the A40/A417 Over roundabout, whereby traffic queues extend back to Highnam and restrict the capacity of the exit from the A40/A48 roundabout. The effect can be allowed for in ARCADY by making a manual adjustment to the capacity of the two approaches, and the effect of this adjustment is also shown in Table 2.1. A lower adjustment was made to the A40 (west) approach in order to produce queues of the right order of magnitude. Although this approach should theoretically have a lower capacity as it gives way to traffic from the A48, the slightly lower queue under these severely congested conditions results from traffic on the A40 approach forcing its way into stationary traffic queuing around the roundabout from the Gloucester exit towards the A48 entry. The results without the correction suggest that, if improvements were made to the capacity of the Over roundabout, some problems would still remain on the A40 approach from Ross in the morning peak period. This results from the imbalance of flows at the roundabout, which prevents full use of the road space on entry.