Highways Agency - Safe roads, Reliable journeys, Informed travellers

Related pages

• 1. introduction
• 2. scheme proposals
• 3. engineering assessment
• 4. environmental assessment
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 4. environmental assessment (continued)
• 5. traffic and economic assessment

5. traffic and economic assessment

5. Traffic and Economic Assessment

5.1 Traffic Analysis

5.1.1 Overview

The traffic analysis undertaken during the assessment of the performance of the CHUMMS Strategy and Alternative Proposal has been fully documented in the Forecasting and Economic Assessment Report: Part II³ with the approach to transport modelling discussed in Part I of this report (Chapter 6). This section summarises the differences between the performance of the highway network under the CHUMMS Strategy and the Alternative Proposal scenarios, and hence the economic case of each.

5.1.2 Network Differences between the CHUMMS Strategy and Alternative Proposal

The CHUMMS Strategy and the Alternative Proposal differ in the nature of the highway link provided between Godmanchester and Spittals.

In the CHUMMS Strategy the existing A14 would be retained as a dual 2 lane standard carriageway road between Fen Drayton and Huntingdon. The existing Huntingdon Railway Viaduct would be removed and an at-grade junction with Brampton Road constructed to retain a route between Godmanchester and Spittals. The precise form of this junction requires more detailed examination; however, for the purposes of running the traffic model, a staggered signalised junction has been assumed. No additional local highway improvements or policy measures have been assumed for the Huntingdon town centre within the traffic model.

Conversely, in the Alternative Proposal the Huntingdon Railway Viaduct would be reconstructed in its current configuration, with a similar level of carriageway provision, and hence no interchange with Brampton Road. On this basis, the new section of the A14 to the south of Godmanchester would only require a dual 2-lane standard carriageway. The rest of the highway network would remain the same as in the CHUMMS Strategy.

5.1.3 Comparison of A14 Journey Times and Route Choice

The key difference between the two options in traffic terms relates to the journey times experienced along the existing A14 between Fen Drayton and the A1(M)/A14 junction near Alconbury. Although the distances are virtually identical in both options, the journey times along this section of the existing A14 are lower in the Alternative Proposal than the CHUMMS Strategy. In 2025, AM peak forecast journey times along the railway viaduct section between Fen Drayton and Alconbury are around 14 minutes in the Alternative Proposal and 20 minutes in the CHUMMS Strategy. This compares to forecast journey times along the new A14 of around 15 minutes in both the CHUMMS Strategy and Alternative Proposal. Table 5.1 provides a summary of distances and forecast journey times between Fen Drayton and both Alconbury and Ellington in 2025 in the AM Peak.

The reduced journey time along the existing A14 in the Alternative Proposal would make this route more attractive for journeys between the south-east of the study area (e.g. Cambridge area, A14 east and M11) and the A1(M) to the north. Traffic would therefore use the existing A14 for these journeys in preference to the new A14 south of Godmanchester, as used by traffic in the CHUMMS Strategy.

For traffic travelling between the south-east and west of the study area (e.g. Cambridge/M11 to Ellington), the new A14 route would provide the quickest and most attractive option in both the CHUMMS Strategy and Alternative Proposal.

The new junction with Brampton Road in the CHUMMS Strategy would primarily provide an additional access for local traffic travelling to and from the Huntingdon area. In the Alternative Proposal this access would not be provided and local traffic travelling to and from Huntingdon would follow the same routes as at present, either along the B1044 via Godmanchester or the A141 via Spittals interchange.

It is noted that the introduction of a junction at Brampton Road in the CHUMMS Strategy would be likely to have implications for local traffic conditions across Huntingdon town centre as traffic patterns would change due to the new access arrangements. Whilst the model is strategic in nature and hence not designed to examine the local impacts within Huntingdon, it does indicate that total delay across the town centre may rise as the new junction increases the number of traffic conflict points in the area. A more detailed study of the local implications of the Brampton Road junction needs to be undertaken, which also considers other potential local transport interventions and policy measures to complement the introduction of the scheme.

5.1.4 Forecast Traffic Flows

The forecast traffic flows for the two scenarios in the vicinity of Huntingdon are given on Figure 5.1 (in Appendix D), which shows the 2010 (opening year) and 2025 (design year) AADT flows. As might be expected, the Alternative Proposal shows an increase in flow on the link to the Huntingdon railway viaduct and a corresponding reduction in flow on the new A14 route south of Godmanchester. Traffic flows along the whole length of the CHUMMS Strategy and the Alternative Proposal are presented on Tables 5.2, 5.3 and 5.4 (in Appendix D) for the forecast years 2010, 2016 and 2025 respectively. The 2016 forecast flows are presented as it represents the end of the Cambridgeshire Structure Plan period.

5.1.5 Design Considerations

Traffic flow ranges for use in the assessment of new rural roads are given in the Design Manual for Roads and Bridges (DMRB) Advice Note TA 46/97. The note gives the economic assessment and recommended flow ranges for new rural road links for opening year AADT flows relating to various carriageway standards. These are set out in Table 5.5 as extracted from TA 46/97. On this basis the required carriageway standards have been identified for each option (Table 5.6 in Appendix D) based on the AADT forecasts for the different sections of the route.

AADT Flows in each direction of travel

5.2 Economic Assessment Process

5.2.1 Overview

The economic assessment of the CHUMMS Strategy and the Alternative Proposal has been fully documented in the Forecasting and Economic Assessment Report Part 2⁴. The approach adopted is also summarised in Part I of this report. This section summarises the approach, setting out the assumptions used only where they differ from those used in the route option assessments documented in Part I of this report. It also summarises the results of the economic assessment.

5.2.2 Costs and Benefits Considered

The economic assessment of the CHUMMS Strategy and Alternative Proposal has been carried out in line with Department for Transport (DfT) and Treasury guidance as detailed on the DfT Transport Appraisal website⁵ and in the Transport User Benefit Appraisal (TUBA) guidance⁶.

In summary, the assessment process was based on a comparison of the total monetised benefits generated by each scheme against its total monetised costs, covering the following four elements:

• The impacts of each scheme on travel times and travel costs for trips made within and through the modelled study area together with the associated impacts on revenue and indirect tax levels. These impacts were estimated on the basis of the forecast change in travel conditions caused by each scheme compared to a Do-Minimum scenario. Conditions in each scenario were forecast using the A14 transport modelling framework, with outputs from the models used to calculate traveller user benefits, revenue and indirect tax benefits using the DfT's TUBA program;
• The impacts of each option on road accidents in the study area. These were estimated using COBA 11⁷ methodology and changes in traffic levels forecast by the transport models;
• The capital and maintenance costs associated with each option. These were derived on the basis of reference schemes and standard rates. Allowances were also made for risk and optimism bias;
• The impacts of the construction and ongoing maintenance programmes on travel times and delay for journeys within and through the study area; estimated using the local highway model and a single year application of the TUBA model.

The approach and underlying assumptions adopted for these assessments has remained largely as those used for the earlier assessment of the route options for the scheme, as reported in Part I of the Technical Assessment Report (TAR)⁸ and Economic Assessment Report (EAR)⁹. The approach is identical for user and provider impacts, accident savings, Do-Minimum costs and construction and maintenance costs. The only change relates to the scheme costs and is detailed in the following section.

5.2.3 Capital Costs of Schemes

The process used to estimate the capital costs of the A14 improvement route options is documented in detail in Part I of the SAR. Details on how the cost estimate has developed since this report is summarised in Section 2.3 of this report.

For the economic assessment and in line with TUBA guidance, the cost estimates were converted to 2002 prices and excluded the VAT and inflation allowances. The Alternative Proposal assessment also included a £21.9 million cost for replacing the Huntingdon Viaduct. This is not considered as part of the total scheme cost because the replacement would be required in any case (i.e. in the Do-Minimum scenario). However, it does need to be included in the economic assessment because the associated cost under the Alternative Proposal differs from that in the Do-Minimum (i.e. the process is cheaper in the Alternative Proposal as the new off-line A14 provides a suitable diversion for many trips and hence a temporary structure parallel to the viaduct would not be required). On this basis the costs incurred in the Do-Minimum but not under the Alternative Proposal have been included as a saving generated by the scheme (as described in Part I of this report). The at-grade junction on Brampton Road is considered to be part of the CHUMMS Strategy and therefore is already included within the scheme cost and therefore the economic assessment.

5.3 Economic Assessment Results

5.3.1 Summary of Results

Tables 5.8, 5.9 and 5.10 provide the summary information from the Transport Economic Efficiency (TEE), Public Accounts and Summary Analysis Tables respectively for each alternative. The tables summarise the costs and benefits associated with each alternative during the 60 year period following opening, disaggregated by benefit type, purpose and vehicle type. The TEE Table (Table 5.8) summarises the impact of each alternative on transport users and the private sector whilst the Public Accounts Table (Table 5.9) summarises the impact on the public sector.

The overall summary results (including the NPV and benefit to cost ratios) are shown in Table 5.10. The NPVs indicate that there is a strong economic case for both alternatives. Of the two, the Alternative Proposal shows the stronger economic case, yielding an NPV of around £2.3 billion compared to approximately £2.0 billion for the CHUMMS Strategy.

• Table 5.7 - Summary of TEE Tables for CHUMMS Strategy and Alternative Proposal
• Table 5.8 - Summary of Public Accounts Table for CHUMMS Strategy and Alternative Proposal
• Table 5.9 - Summary Analysis Table for CHUMMS Strategy and Alternative Proposal
• Download tables 5.7 to 5.9 (40KB PDF)

Overall the pattern of costs and benefits are similar for both alternatives. The following highlights a number of key findings drawn from the tables:

• There is a strong economic case for the schemes. The BCRs (showing the ratio of benefit to central Government's cost) and the BKRs (showing the ratio of benefit to the HA's cost) are considerably greater than 1, demonstrating that the economic benefits of both schemes exceed their costs. The BCRs are 19.6 and 21.4 for the CHUMMS Strategy and Alternative Proposal respectively and the BKRs 6.1 and 7.1.
  
  
• For both schemes, the majority of benefits are derived from highway time savings. Travellers using the new route in both schemes would experience savings between Ellington and Fen Ditton of up to 8 minutes in the westbound direction and 20 minutes eastbound (compared to the Do-Minimum in the AM peak, 2016).
  
  Travellers using the existing A14 would also experience savings relative to Do-Minimum journey times. In the CHUMMS Strategy (where the Huntingdon railway viaduct would be replaced by an at-grade junction on Brampton Road) journey times would be approximately 2 minutes lower in the westbound direction and 7 minutes lower eastbound (between Ellington and Fen Ditton in the AM peak, 2016). These are relatively modest savings and therefore benefits would mainly be experienced by those using the new route which would offer considerably shorter journey times than the existing route.
  
  In the Alternative Proposal (where the existing A14 and the viaduct would be retained), traffic and consequently time related benefits would be more evenly split between the two routes. Journey times along the existing A14 would be comparable to those along the new route and up to 2 minutes lower for journeys between the south-east of the study area (i.e. the Cambridge area, M11 and A14 east) and the A1(M), for which the existing road and retained viaduct would provide a more direct route than the new off-line road and the A1.
  
  During an average weekday, the value of savings accrued during peak hours in both schemes are approximately 10% greater than those accrued during the non-peak. The annual weekend (and bank holiday) savings equate to approximately 20% of the total value of savings experienced over the working days of the year.
  
  It is noted that, in the CHUMMS Strategy, time benefits are offset to a degree by a forecast increase in localised congestion and delay within Huntingdon. This is caused by the potential increase in route conflict and associated delay which could be caused by the introduction of an at-grade junction to replace the viaduct. The model forecasts less delay in Alternative Proposal, where the reinstatement of the viaduct would mean that Do-Minimum travel patterns remained largely undisrupted. However, the model is strategic in nature and not designed to examine local impacts and changes in traffic flow within Huntingdon. As discussed above, a more detailed study is required to examine the local impacts of the Brampton Road junction, including consideration of other potential complementary local transport interventions and policy measures. Such a study would provide more accurate indications of the local impacts of the CHUMMS Strategy and Alternative Proposal in the Huntingdon area and the implications for their economic performance.
  
  The overall time savings in both alternatives are also offset to some degree by delays experienced during the construction process. In the CHUMMS Strategy, the construction related losses equate to approximately 4.5% of the total time savings generated by the scheme. In the Alternative Proposal they equate to 6.5% of total savings. The losses are larger in this alternative because the construction period for the new railway viaduct in Huntingdon could last up to 2 years compared to the possible 6 to 9 month construction period for the at-grade junction in the CHUMMS Strategy.
  
  
• Both alternatives generate accident savings. The implementation of either the CHUMMS Strategy or the Alternative Proposal would have two main impacts with opposing influences on accident numbers. The introduction of a new, high quality road link between Ellington and Fen Ditton on one hand would tend to result in fewer accidents, but on the other hand, slightly increasing the average distance travelled would act to increase the number of accidents. The combined effect of these impacts would be to reduce the annual number of accidents by nearly 150 personal injury accidents (PIAs) by the year 2025 in the CHUMMS Strategy and by over 2900 total accidents including PIAs and damage only accidents. The savings associated with the Alternative Proposal would be smaller in scale (around 130 PIAs and 2600 total accidents) because the reinstatement of the Huntingdon railway viaduct would cause more traffic to continue to use the existing A14. Consequently, less would divert to the new off-line route which would be designed to more modern standards and hence have a lower expected average accident rate.
  
  The reduction in accidents equates to less than 3% of annual accidents in the study area in both schemes. However, in monetary terms the savings generate an NPV of around £310 million in the Alternative Proposal and £335 million in the CHUMMS Strategy, representing approximately 15% of the present value of benefits (PVB).
  
  
• There is a net increase in fuel and non-fuel vehicle operating costs. The magnitude of this increase equates to between 8% and 13% of the monetary value of the time savings for each alternative. The changes are primarily due to the slight increase in average distance travelled per journey, as the new A14 route influences travel patterns causing more drivers to make longer distance trips as they take advantage of the improved route. One contributory factor to the increase in distance in the CHUMMS Strategy is the fact that the journey from the south-east of the study area (i.e. the Cambridge area, M11 and A14 east) and the A1 (M) to the north is around 4.5 km longer using the new route than the existing A14. This has less influence in the Alternative Proposal where the reinstatement of the viaduct causes drivers to continue using the more direct route along the existing A14.
  
  Despite the relatively large increase in vehicle operating cost for these trips, it only represents a very small change in the total vehicle operating costs associated with highway travel in the modelled area (less than 1%).
  
  
• Both alternatives generate increased indirect tax revenues for central Government. This is largely due to increased expenditure on fuel and non-fuel related highway costs brought about by the slight increase in average travel distance caused by the schemes.
  
  

5.3.2 Reliability

The economic assessments presented do not include a monetised estimate of reliability benefits because the methodology for quantification is still under development and any results are considered provisional. However, both the CHUMMS Strategy and Alternative Proposal should produce reliability improvements through a number of effects.

Firstly, both would provide increased capacity and therefore reduced stress on the network, improving performance and providing more flexibility to cope with incidents and with fluctuations in capacity and demand. Additionally, the improvements are forecast to reduce accidents and therefore the number of incidents occurring and influencing journey time reliability. Finally, through providing a new section of road, the improvements would provide a new alternative route for a long section of the corridor, helping to mitigate the impacts of incidents by providing more options for diversion routes. In the Alternative Proposal this contribution to improved reliability would be particularly marked because the retention of the existing A14 would result in this section of the corridor being served by two trunk roads.

3. A14 Ellington to Fen Ditton, Forecasting and Economic Assessment Report Part 2, by Atkins on behalf of the Highways Agency (February 2005) back [3]
4. A14 Ellington to Fen Ditton, Forecasting and Economic Assessment Report: Part 2, by Atkins on behalf of the Highways Agency (February 2005) back [4]
5. http://www.webtag.org.uk back [5]
6. TUBA User Guidance and User Manual, Version 1.6A, prepared by Mott MacDonald on behalf of the DfT, June 2004. TUBA is the DfT's bespoke software for carrying out economic assessments of the impacts multi-modal transport schemes. back [6]
7. The COBA Manual: DMRB, Volume 13, Section 1, Part 2: The Valuation of Costs and Benefits back [7]
8. A14 Ellington to Fen Ditton, Technical Appraisal Report Part I, Chapter 8 Economic Assessment, by Atkins on behalf of the Highways Agency (February 2005) back [8]
9. A14 Ellington to Fen Ditton, Economic Assessment Report Part I, Final Draft, by Atkins on behalf of the Highways Agency (October 2004) back [9]