Economic, Environmental and Social Impacts of Changes in Maintenance Spend on Local Roads in Scotland
Appendix L Scaling-up the Sample Analyses
L.1 Vehicle operating costs due to reduced carriageway condition
For each sample Authority, the vehicle operating cost was calculated for each vehicle type (i.e. HGV, bus, car and van) and road type (i.e. A, B, C and U roads) for urban and rural areas.
The representative factor, , for vehicle operating cost, for each vehicle type and each road type was calculated as shown in equation (K1).
| f = 1 / [(T/LT)(LR/LT)] | (K1) |
where is the traffic (vehicle km) in 2009 for that vehicle type on that road type, , - . is the total length of that road type and , - . is the length of that road type in poor condition (i.e. categorised as red in the SRMCS report for 2009/10).
Where there is more than one sample Authority of the same type, to calculate the factor for that Authority type, the values are the total for all sample Authorities of that type.
To calculate the fingerprint for the Authority type for vehicle operating costs, for each road type and vehicle type:
1. Divide the total traffic by the total length of road to give the number of vehicles (A)
2. Divide the total length of road in 'red' condition by the total length of road to give the proportion of the network in poor condition (B)
3. Multiply A by B to give C, the inverse of the factor (i.e. C=,1- .)
4. Divide the vehicle operating cost by C to give the fingerprint, D, for the road type and vehicle type
To scale the values for each new Authority of that type not in the sample of 8 Authorities, for each road type and vehicle type:
5. Calculate the inverse of the factor CN for the new Authority, following steps 1 to 3
6. Multiply D by CN to give the vehicle operating cost for the new Authority.
The change in vehicle operating cost for the network is the sum of the change in vehicle operating costs for all Authorities, all road types and all vehicle types.
The total vehicle operating cost for the network was the sum of each of the costs for all road types and vehicle types in all Authorities (where the sample Authorities included more than one Authority of the same type, the results from each sample Authority were used in the total cost for the network, not costs derived using the representative factors for that Authority type).
L.2 Journey time costs due to reduced carriageway condition
The increase in journey time due to deterioration of the road condition has been calculated for the urban and rural A roads and each vehicle type in each of the sample Authorities. The scaled values for the entire network are therefore also estimated only for A roads in the network. For each Authority not in the sample Authorities, the representative factors for the costs, for each road type and vehicle type are calculated in the same way as the vehicle operating costs described in Section L.1.
L.3 Costs of vehicle emissions due to reduced carriageway condition
As the condition of the road surface changes, there are changes in vehicle speeds and this leads to changes in the amount of emissions (e.g. CO2) from the vehicles. Analysis of the traffic and road conditions in the 8 sample Authorities has estimated the cost/benefit of the changes in the emissions for each combination of vehicle type and road type in each Authority type.
The effect of the change in emissions for the Authorities not in the 8 sample Authorities was estimated using the same approach as described for vehicle operating costs in Section L.1.
L.4 Journey time costs due to roadworks
In each of the 8 sample Authorities, the length treated on a road type divided by the assumed (notional) scheme length for the treatment type and road type gave an estimate of the number of schemes of that treatment type on that road type in each sample Authority.
The result from the analysis of the cost of increased journey time associated with each maintenance scheme is then used with the numbers of schemes to give the total cost of the change in journey time due to maintenance for each treatment type on each road type in each of the 8 sample Authorities. For the scaling up of these costs, the total costs for all treatment types were used for each road type.
To determine the total cost for all road types in all Authorities, an approach similar to that used for the change in vehicle operating costs due to change in road surface condition, described in Section L.1. However, rather than using the level of traffic as a prime factor in the scaling, the amount of maintenance (i.e. the number of schemes) is assumed to be related to the maintenance budget for structural maintenance.
The representative factor, , for journey time costs due to roadworks, for each road type was calculated as shown in equation (K2).
| f = 1 / [(S/LT)(LR/LT)] | (K2) |
where is the structural maintenance budget (£) for 2009/10, , - . is the total length of the road type and , - . is the length of that road type in poor condition (i.e. categorised as red in the SRMCS report for 2009/10).
Calculation of the fingerprint for the Authority type for the costs of increased journey time for each road type was carried out as described in steps 1 to 6 in Section L.1 but using the total structural maintenance budget instead of traffic in the calculation of B in step 2.
The total cost of increased journey times due to maintenance for the network was the sum of each of the costs for all road types and vehicle types in all Authorities (where the sample Authorities included more than one Authority of the same type, the results from each sample Authority were used in the total cost for the network, not costs derived using the representative factors for that Authority type).
L.5 Costs of CO2 from roadworks
In addition to the costs of increased journey time due to maintenance, the costs of CO2 associated with maintenance works was also estimated for the whole network based on the results of the analyses for the 8 sample Authorities.
The amount of CO2 is assumed to be related to the number of maintenance schemes and the costs for each road type in each of the Authorities not included in the sample Authorities was calculated in the same way as the costs of increased journey times due to maintenance described in Section L.4.
L.6 Depreciated replacement cost
The accumulated depreciation for each road type in the network in each of the 8 sample Authorities has been provided by WDM Ltd using the approach adopted for the estimate of depreciation of the road asset for the Spending review analysis in 2010.
The effect of the depreciation of the road networks in each of the Authorities not included in the 8 sample Authorities was estimated in a similar way to the approaches adopted for the other aspects of costs.
The representative factor, , for the accumulated depreciation costs, for each road type was calculated as shown in equation (K3).
| f = 1 / LR | (K3) |
where , - . is the length of that road type in poor condition (i.e. categorised as red in the SRMCS report for 2009/10).
To calculate the fingerprint for each road type in the Authority type divide the total depreciation cost by the total length of road in poor condition, to give the cost per kilometre of road in poor condition (D) for that Authority type.
To calculate the depreciation cost for each road type in each Authority not in the sample Authorities multiply D by the length of road in poor condition to give the depreciation cost for the non-sample Authority.
The total depreciation cost for the network was the sum of each of the costs for all road types in all Authorities (where the sample Authorities included more than one Authority of the same type, the results from each sample Authority were used in the total cost for the network, not costs derived using the representative factors for that Authority type).