Economic, Environmental and Social Impacts of Changes in Maintenance Spend on Local Roads in Scotland
Appendix H Analysis of Roadworks and Delay Costs
The user delay costs at roadworks were calculated using the treatment length data provided by the WDM model runs and outputs from the DfT Queues and Delays at Roadworks (QUADRO) user delay cost model (Highways Agency, 2009b).
Treatment length data from WDM was by road type, road environment, treatment type and time period. The lengths provided were aggregated over 5 time intervals:
- 2010 to 2012 (3 years)
- 2013 to 2016 (4 years)
- 2017 to 2019 (3 years)
- 2020 to 2024 (5 years)
- 2025 to 2029 (5 years)
To determine the treatment length data within each year the treatment lengths and areas were divided by the number of years in the corresponding time interval. The resulting annual treatment lengths and areas were then used in the subsequent analysis. The proportioning of the treatment lengths and areas evenly across the time intervals in this manner meant that the treatment lengths between 2020 to 2024 and 2025 to 2029 were not commensurate with the linearly increasing budgets for scenarios 2 and 3 during these time intervals. The effect of this can be seen by the sudden changes in delay costs results for 2020 and 2025.
From the treatment lengths a number of notional schemes were calculated for each year in the analysis period, assuming a 250m scheme length for single carriageway and a 1000m scheme length for dual carriageways.
Using the traffic data for each of the Local Authorities by road type and the network length of each road type a traffic flow was calculated for each type of road in each Authority. The proportion of HGVs in the traffic flow was also calculated. Using these flows and the notional closure lengths of 250m and 1000m a series of QUADRO runs were carried out to calculate the user delays of a single scheme for each Local Authority, road type, carriageway type, road environment, and year of the analysis period (taking into account the growth in traffic). The resulting delay costs were then multiplied by the number of schemes calculated from the treatment length data to obtain an overall delay cost for each year of the analysis period for each sample Authority.
The user delay costs for each of the modelled years under the 20% and 40% budget cut scenarios were then linearly interpolated and extrapolated to represent a 35% and 69% budget cut to account for the fact that the WDM model runs were carried out using a 20% and 40% budget cut, but the subjective budget analysis identified that these would be equivalent to a 35% and 69% budget cut in carriageway maintenance respectively.
H.2 Results
The results of the analysis are shown in Figure H.1 to Figure H.8. The analysis shows that Edinburgh will experience the largest delay costs of all the sample Authorities, which is rational since delay costs are sensitive to traffic and Edinburgh has high traffic flows. Surprisingly this behaviour is not observed in the Glasgow results. Further analysis shows that Glasgow and Edinburgh have similar network condition, with Glasgow having a longer network length compared to Edinburgh. The difference is that Glasgow has a significantly smaller budget compared to Edinburgh and consequently less carriageway maintenance schemes. This demonstrates that the analysis is highly sensitive to the amount of maintenance and by association the maintenance budgets set.
Figure H.1 Aberdeenshire delay costs at roadworks
(2002 prices undiscounted)
Figure H.2 Dumfries and Galloway delay costs at roadworks
(2002 prices undiscounted)
Figure H.3 City of Edinburgh delay costs at roadworks
(2002 prices undiscounted)
Figure H.4 Fife delay costs at roadworks
(2002 prices undiscounted)
Figure H.5 Glasgow City delay costs at roadworks
(2002 prices undiscounted)
Figure H.6 Highland delay costs at roadworks
(2002 prices undiscounted)
Figure H.7 North Lanarkshire delay costs at roadworks
(2002 prices undiscounted)
Figure H.8 South Ayrshire delay costs at roadworks
(2002 prices undiscounted)
H.3 Effect of discounting
The User Delay Costs were discounted by 3.5% per year. The effect of this discounting can be seen in Figure H.9 for Fife.
Figure H.9 Fife delay costs at roadworks
(2002 prices discounted)
