The analyses were intended to provide an indication of the magnitude of the impacts due to potential reductions in maintenance spending. As with any such strategic study of network level impacts, key assumptions had to be made to account for the extent of data and resources available. The analyses have been carried out in accordance with the Scottish Transport Appraisal Guidance (STAG) (Transport Scotland, 2011a) (Transport Scotland, 2011a) and where relevant the UK Department for Transport, Transport Appraisal webTAG Guidance (Department for Transport, 2011a). Where this has not been possible, the report notes the assumptions that have been adopted.
A comprehensive literature review was conducted to identify as much relevant available evidence as possible. The review also took account of various published or unpublished evidence supplied by WG4 members. The review enabled a qualitative analysis to be completed which identified the potential impacts of the funding scenarios.
2.1 Local Authority road networks
For the quantitative analyses, two initial steps were needed before undertaking a detailed assessment of the impacts of the funding reductions:
- The scenarios are broadly defined (i.e. a base case assuming current funding levels and two alternatives assuming 20% and 40% reductions), but they do not describe the practical implications on changes in actual road maintenance activity. For example, for the 20% reduction in funding, a Local Authority might choose to maintain its current expenditure on street lighting and winter maintenance, but make more significant cuts (i.e. greater than 20%) to the carriageway surfacing budget, to achieve an overall 20% reduction.
- To assess many of the impacts, it was not feasible to conduct the same analysis for each of the 32 Local Authorities. Instead, a sample of Authorities was, therefore, selected for detailed analysis. These Authorities were considered reasonably representative of the whole local road network. The results from the sample Authorities could then be scaled to represent the impact on all the local road network.
The network varies from remote rural roads to major city networks. SCOTS has adopted a referencing approach which classifies each Local Authority network into one of five categories (city, urban, semi-urban, rural and island). For most of the analyses described in later Sections, eight Local Authorities have been analysed in detail:
- City - Glasgow City
- Rural - Dumfries and Galloway
- City - City of Edinburgh
- Semi-urban - Fife
- Rural - Aberdeenshire
- Semi-urban - South Ayrshire
- Rural - Highland
- Urban - North Lanarkshire
The full list of 32 Authorities and the associated categories is given in Appendix D. For the scaling of the sample results to the full network, Island Authorities have been considered as rural Authorities where necessary. Results for individual Authorities, excluding the 8 sample Authorities, are not provided. Authorities are identified only by the Authority category.
To examine the effects on different types of Authority, the sample Authorities were selected to include rural, urban, semi-urban and city Authorities. Within each Authority, where appropriate, the network was analysed by road class (A, B, C and U) and urban/rural.
To assess the impacts related to traffic, the vehicles have been considered in terms of cars, light goods vehicles (LGVs), buses and heavy goods vehicles (HGVs).
All analyses have taken into account the expected growth in the level of traffic through the analysis period, changes in economic parameters (e.g. values of time and accidents) and improvements in engine efficiency for vehicle operating costs.
For the analyses, the maintenance budget assumed for 2010/11 for each of the Local Authorities was that agreed for the Spending Review 2010 analyses of maintenance funding. The budgets are given in Appendix C.
In practice, since the 2010/11 budgets were set, these have been reduced so the effects of reduced budgets are already being seen. This study has been restricted to examining the effects of the reductions to the Spending Review 2010 budgets.
2.2 Network condition analyses
To assess the effect of the funding levels in each of the sample Local Authorities, WDM Ltd was contracted to run the road condition prediction model to predict the condition of each road type in each Authority (the analyses were run separately for each Authority and each Scenario). The model uses data for 2009/10 collected from SCANNER surface condition surveys to predict the condition of the network in each year of the analysis period (i.e. between 2010/11 and 2029/30) using the appropriate budget in each year. To limit the volume of results produced from these analyses, the outputs from the condition predictions only for the years 2010, 2013, 2017, 2020, 2025 and 2030 were stored at the end of the analyses. The results included:
- Predicted carriageway condition parameters including longitudinal profile variance for each 10m carriageway length in an asset database for the 8 Authorities
- Treatment types, lengths and areas for each of the time intervals used in the model (i.e. 2010 to 2012, 2013 to 2016, 2017 to 2019, 2020 to 2024 and 2025 to 2029).
To obtain the annual values for the results, the results for each time step (e.g. between 2010 and 2013) were divided equally between the years in the time-step. This can lead to apparent jumps in the results between time steps but was considered sufficiently reliable for overall network analyses of this type.
Using a separate asset valuation, condition analysis model, WDM also produced estimates of the cumulative depreciation for each road type in each sample Authority.
Both the condition prediction model and the valuation model have been used for Local Authorities in Scotland for several years. It was agreed that this study would take the results from the runs of the models and not be concerned with changing the analysis method, input data or results produced.
The predicted condition for each of the road types in the sample Authorities when combined with other data (e.g. traffic) formed the basis of the further analysis of the wider economic costs and benefits (e.g. vehicle operating costs).