What Are the Wider Impacts of Changes to Road Maintenance Budgets?
K Johnston, Transport Scotland; T Bradbury, C Parkman, R, Abell, TRL, UK
A quantitative and qualitative analysis of the social, environmental and economic impacts resulting from changes in road maintenance budgets, including modelling of vehicle, user and environmental costs; and sensitivity analysis of key assumptions.
In 2011, the Scottish Government established a National Road Maintenance Review to consider improvements to the management and maintenance of all Scotland's roads. As part of this review, the economic, environmental and social impacts of potential changes in maintenance spend were explored.
Traditional cost benefit analyses were combined with qualitative assessments of impacts and provided key evidence supporting the Roads Maintenance Review of trunk and local roads in Scotland by using a fusion of established modelling techniques and novel approaches to assess the impacts of maintenance budget cuts over a 20 year time horizon - the first time a comprehensive analysis of this type has been undertaken.
The quantitative economic impacts assessed by the study were: vehicle operating costs; user delay costs; accident costs and the environmental costs of greenhouse gas emissions (CO2). Qualitative impacts considered were: noise and vibration; air quality; water quality; biodiversity; visual amenity; and security.
Three road maintenance budget scenarios that considered 10 years of cuts and 10 years of recovery were explored: Scenario 1 (a baseline budget scenario) - broadly maintain current road maintenance budgets; Scenario 2 - Reduce Scenario 1 funding levels by 20% for 10 years; and Scenario 3 - Reduce Scenario 1 funding levels by 40% for 10 years.
Results from Transport Scotland's pavement investment model were used as the basis for assessing impacts on the trunk road network condition. For the local road network, due to the number of separate networks a sampled approach was used which built on the outputs from the SCOTS pavement investment model.
Vehicle operating costs were assessed using the HDM-4 road user cost model adjusted to suit the Scottish context. Differences in vehicle operating costs for the different scenarios were based on the impact of projected differences in road conditions.
User delay costs through roadwork sites were modelled using a number of notional maintenance schemes based on the projected levels of maintenance and predicted traffic levels on the network. Estimation of teh costs of delays to road users due to small reductions in vehicle speed, based on previous UK evidence was also included in the user delay cost analysis.
Accident costs due to changes in the levels of road lighting and variations in skid resistance were calculated. Historic accident data was assessed and for each scenario, using assumptions based on empirical UK evidence, different numbers of accidents for each scenario were postulated.
The calculation of carbon emissions costs used three separate analyses: first, the change in carbon emissions from vehicles delayed through roadwork sites; second, an assessment of the embodied CO2 in the construction materials; and third, the change in carbon emissions from vehicles due to changes in pavement roughness.
Assumptions were needed at each step of the analysis, in order to complete the quantified analyses. The paper highlights the key assumptions and explains how the relevant effects were addressed in the analysis. The paper describes the results of sensitivity testing which showed that the most significant assumptions on the analysis relate to the trade off between vehicle operating costs and projected road conditions.
The key conclusion from the study was that the whole life economic impacts of reductions to road maintenance budgets outweighs the savings in the whole life costs of maintenance works achieved from the budget reductions. Therefore, It is essential the wider impacts of maintenance budget reductions are considered when assessing how to save money from roads maintenance.
Association for European Transport