Economic, Environmental and Social Impacts of Changes in Maintenance Spend on the Scottish Trunk Road Network
8 Impacts of pavement operations
8.1 Overview
The impact of pavement maintenance operations on travel time has been assessed using the current UK approach for assessing road maintenance. The Highways Agency Pavement Management System (HAPMS) includes a module to evaluate the whole life costs of different pavement maintenance options, known as SWEEP (Software for the Whole-life Economic Evaluation of Pavements). The SWEEP model adopts current parameter values to assess the impact of works in terms of the costs of delays to road users under different traffic management arrangements at maintenance sites.
The analysis approach was applicable for this study, subject to the input values being based on the typical range of works operations undertaken on the Scottish trunk road network. This Section sets out the background to this analysis and the results obtained for the Scottish trunk road network.
8.2 Pavement roadworks and travel delay costs
8.2.1 Scheme data
Scheme data based on the estimated area of work (m2) was obtained for each treatment type for the last 10 years. The breakdown of treatment type by road type was calculated using the historic scheme data obtained from the asset database, as shown in Table 8.1. This allowed the maintenance work to be broken down by road type.
For the analysis of the cost of delays to road users, the quantity of maintenance work was split into notional schemes. The analysis in Section 3.6 shows that the average length of scheme is between 500m and 900m for all road types and years. To account for tapers in and out of the works a notional scheme length of 1500m was selected for dual APTRs and Motorways. A notional scheme length of 500m was selected for Single APTRs.
8.2.2 Treatment durations
To estimate the delays to road users it was necessary to assess the duration of each notional scheme (i.e. the number of days/nights of traffic disruption). The default treatment output rates in SWEEP were used to estimate the duration of work for the notional schemes.
Table 8.2 shows the treatment thicknesses assumed in the analysis.
|
Treatment Type |
Treatment Thickness (mm) |
|---|---|
|
Reconstruction |
300 |
|
Strengthening |
100 |
|
Surface treatment |
30 |
To calculate the duration of the maintenance work it was assumed that one lane within the notional scheme length is closed at any one time. Using the scheme length, the area treated (assuming the width of a lane is 3.65m) was calculated and using the output rates, the duration (in hours) was obtained.
8.2.3 Delay costs
QUeues And Delays at ROadworks (QUADRO) is a Department for Transport (Highways Agency, 2009) sponsored computer program which estimates the effects of roadworks in terms of time, vehicle operating and accident costs on the users of the road. Individual roadworks can be combined to produce the total cost of maintaining the road over time. For this analysis, the delay cost for each day of each notional scheme was calculated. The total delay cost per scheme was calculated by multiplying the duration (as described in Section 8.2.2) by the delay cost per day. The total cumulative delay cost of all notional schemes gave the total delay cost for each year of each scenario.
8.3 Analysis results
For each of the three scenarios, the total delay cost per year was calculated using the methodology described in Section 8.2. Over the first 10 years of the analysis (i.e. while budgets were reduced in Scenarios 2 and 3), for a 20% reduction in pavement budgets (Scenario 2), the total delay cost savings (relative to Scenario 1) ranged from 19% to 34%. For a 40% reduction in pavement budgets, the total delay cost savings (relative to Scenario 1) ranged from 27% to 39%. The overall delay cost savings relative to the costs of delays to road users that would be incurred over the first 10 years of the analysis, with the current budget level, are shown in Table 8.3. In the second 10 years of the analysis, as budgets increase and the amount of maintenance increases in Scenarios 2 and 3, the differences between the scenarios is removed.
Figure 8.1 shows the total annual undiscounted delay costs for each scenario over the 20 year period.
The results of the analysis show the reductions in pavements budgets would lead to reductions in the amount of work and hence less disruption to traffic on the network. The annual variation in delay costs shown in Figure 8.1 arises as the number of notional schemes on each road type changed over the analysis period.
|
Scenario |
Average Annual Delay Cost Saving Compared to Scenario 1 |
|---|---|
|
Scenario 2 |
26% |
|
Scenario 3 |
33% |
Figure 8.1 Total annual delay cost for each Scenario