Second Avon Crossing Transport Modelling
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TECHNICAL MEMORANDUM Second Avon Crossing Transport Modelling PREPARED FOR: Bristol City Council DATE: December 5th, 2016 PROJECT NUMBER: 673846.AO.14.01 STATUS: Final WRITTEN BY: Toufik Al-Joura / Chris Bushell APPROVED BY: Chris Bushell 1.0 Introduction 1.1 Overview CH2M have been commissioned by Bristol City Council (BCC) to undertake transport modelling and cost benefit analysis associated with two potential alignments for a second bridge crossing of the river Avon, in the vicinity of the existing M5 crossing. The new crossing is referred to as the Second Avon Crossing (SAC). 2.0 Scheme Assumptions 2.1 Options AECOM have been commissioned to undertake a feasibility study for various SAC options. This has identified possible options as shown in Figure 1. As advised by BCC, the options assessed by CH2M are Options 1 and 31. 2.2 Design assumptions In each option the SAC has been assumed to have one lane per direction. Due to the preliminary stage of option development, junction designs have not yet been produced for locations where the SAC will interact with the existing road network. Hence assumptions have been agreed with BCC / AECOM relating to the form of junction at each relevant location. Further, junctions have been coded on the basis that it is assumed sufficient capacities will be incorporated into junction designs to accommodate SAC traffic volumes. Table 1 indicates the assumed junction forms at relevant locations. A4 Portway A369 Gordano Way Victoria Rd Marsh Ln Option 1 Signal Signal N/A N/A No connection Option 3 Signal N/A Priority N/A roundabout Table 1 – Assumed Junction Types 1 Option 3 includes the part of Option 2 over the River Avon to connect to the A4 Portway 1 SECOND AVON CROSSING TRANSPORT MODELLING Figure 1 – SAC Options identified in AECOM study 2.3 Scheme Costs Costs for each option have been provided by AECOM. A further nominal allowance of 5% has been made for land and operating / maintenance costs over the assessment period (60 years). 44% Optimism bias has been applied in accordance with DfT guidance, in addition to 15% risk / contingency. Since AECOM have included an inflation allowance of 12.6% from the time of cost estimation (2016) until mid construction (2019), costs have been adjusted so as only to include cost increases in real terms (i.e. excluding general inflation, as advised by TAG). This has resulted in a net cost decrease of around 6% based on the GDP deflator, as per the WebTAG Databook (July 2016). Table 2 shows the costs for each option (2016 £ values and prices). 2 SECOND AVON CROSSING TRANSPORT MODELLING Option 1 Option 3 Base costs 147,192,679 159,429,600 Operating cost 3,679,817 3,985,740 Land 3,679,817 3,985,740 Optimism bias 68,003,018 73,656,475 Total 222,555,330 241,057,555 Table 2 – Scheme Costs 3.0 Methodology 3.1 Overview The GBATS4M transport model of the Greater Bristol area has been used to test the SAC options. Scenarios have been modelled in the AM peak, inter-peak (IP) and PM peak models with forecast years of 2021 and 2036. This model contains assumptions about planned developments and schemes within the model area, in accordance with DfT guidance. Table 3 details the total additional homes/jobs explicitly assumed in the future year Reference Case models (excluding smaller sites less than 1 hectare for employment sites less than 50 homes for housing). The forecasts are also controlled to Tempro growth in line with DfT guidance. Car trips are forecast to increase by around 20% by 2036. Year Additional New Homes Additional New Jobs 2013-2021 27,719 34,621 2021-2036 7,656 16,937 2013- 2036 35,375 51,559 Table 3 - Additional Planned Development included in Do Minimum Further information on the model development is contained in GBATS4M MetroWest Do Minimum Forecasting Report, February 2016. To identify monetary impacts, TUBA2 software was used which incorporates the DfT’s Transport Appraisal Guidance (TAG) economic parameters issued in December 2015. 3.2 Transport Modelling To assess the new crossing options, the relevant highway links and connections were coded into the modelled network. The model was then re-assigned using a fixed demand highway assignment. Checks have been undertaken to ensure that local capacity constraints do not unduly limit the operation of the SAC in the model runs undertaken. No bus routes have been altered in the assessment. 3.3 Monetary Impacts Monetary impacts have been identified over a 60 year appraisal period using the DfT TUBA software in line with DfT guidance. Expansion factors were applied based on local data to calculate peak period and inter-peak period impacts from the modelled hours as follows: 2 Transport User Benefits Assessment version 1.9.6 3 SECOND AVON CROSSING TRANSPORT MODELLING AM : 2.55 IP : 6 PM : 2.56 Further expansion to annual impacts were derived assuming 253 weekdays per year. TUBA uses value of time (VOT) parameters in line with DfT guidance which vary by trip purpose and traveller income group. Car driver 2015 values are as follows: Employers’ business: £26.54 / hour Non-work low income: £5.31 / hour Non-work medium income: £6.76 / hour Non-work high income: £8.54 / hour Appendix A gives further details of the TUBA guidance ‘consumer surplus’ calculations which have been employed. 4.0 Scheme Assessment 4.1 Traffic flows Table 4 provides the 2036 forecast traffic flows on the SAC for each option assessed in terms of passenger car units (PCUs) per hour. The modelling assignments indicate that 80-90% of the trips to use the new crossing would be diverted from the existing M5 crossing, with the remainder drawn from other routes. Option 1 Option 3 AM IP PM AM IP PM Eastbound 431 205 278 424 276 374 Westbound 539 327 751 691 384 878 Total 970 532 1029 1115 660 1252 Table 4 - SAC Traffic Volumes (PCUs) This shows that SAC flows for Option 3 are slightly higher than those for Option 1 by around 15 to 20%. Table 5 provides modelled traffic flows for the M5 Avon crossing as a comparison, for each option post- construction of the new crossing. This indicates that the SAC is forecast to carry up to around 10% of the corresponding M5 volumes in the peak hours and around 5% in the inter-peak hours. Option 1 Option 3 AM IP PM AM IP PM Eastbound 6404 5148 5517 6445 5081 5456 Westbound 4701 4860 5945 4632 4844 5836 Total 11105 10008 11462 11077 9925 11292 Table 5 - M5 Traffic Volumes (PCUs) 4.2 Cost Benefit Analysis Table 6 gives the results of the cost benefit analysis, as per section 3.3.and Appendix A, reflecting re- routing of trips and associated reduced journey times and distances in aggregate across the network. Monetary values are presented in 2010 prices and values as per DfT guidance. 4 SECOND AVON CROSSING TRANSPORT MODELLING Option 1 Option 3 Present Value of Benefits (PVB) 70,867,023 83,937,082 Present Value of Costs (PVC) 148,101,136 160,414,495 Net Present Value (NPV) - 77,234,113 - 76,477,413 Benefit Cost ratio (BCR) 0.48 0.52 Table 6 - Cost Benefit Analysis The CBA results indicate that whilst Option 3 performs slightly better than Option 1, both options yield a low BCR value due to limited benefits relative to the scheme costs. It should be noted that the SAC may offer network resilience benefits, e.g. as an alternative route during incidents on the M5, which are not represented in this assessment. 5.0 Limitations 5.1 Overview It is advised that the assessment undertaken is a preliminary assessment to identify the broad level of benefits expected from the SAC. This has been undertaken using the GBATS4M highway model which was not developed specifically for the assessment of this scheme. The scheme assessment is potentially sensitive to the trip composition of users of the M5 crossing, particularly in relation to the mix of local verses long distance trips. Further tasks that have not been undertaken, but would be recommended for a more detailed assessment, include: ANPR survey (or similar) to gauge local traffic levels using M5 bridge select link analysis of modelled M5 traffic adjustment of model to reflect local / strategic traffic mix on M5 bridge by vehicle type check of M5 bridge volumes against data and adjustment for significant differences check of nearby M5 junction volumes against data and adjustment for significant differences junction assessments of affected local junctions used for SAC access, such as M5 J19, A4 Portway etc. review of highway network performance and constraints, and further potential network optimisation / enhancements analysis of SAC users analysis of scheme benefits, including spatial disaggregation assessment of network resilience benefits, such as scheme benefits if M5 closures / restrictions occur, accounting for expected incident frequency. 6.0 Conclusions 6.1 Results The assessment above indicates that the SAC would carry around 10% of the corresponding M5 volumes in the peak hours and around 5% in the inter-peak hours. Option 3 is forecast to carry slightly higher volumes than Option 1. The modelling assignments indicate that 80-90% of the trips to use the new crossing would be diverted from the existing M5 crossing, with the remainder drawn from other routes. The cost benefit analysis undertaken indicates BCRs are relatively low for both options considered, at 0.48 and 0.52 for Options 1 and 3 respectively. These values have been calculated as per section 3.3.and 5 SECOND AVON CROSSING TRANSPORT MODELLING Appendix A, reflecting re-routing of trips and reduced journey times and trip distances in aggregate across the network.