Economic, Environmental and Social Impacts of Changes in Maintenance Spend on Local Roads in Scotland

10 Environmental Impacts

10.1 Carbon emissions

Under each of the budget scenarios there are differences in the amount of maintenance carried out on the network. Changing the amount of maintenance carried out has an impact on the network CO2 emissions in a number of ways:

  • Reducing the amount of maintenance activity or the invasiveness of maintenance treatments reduces the amount of CO2 emitted in carrying out the work and the CO2 embodied in the materials used (e.g. asphalt).
  • Reducing the amount of maintenance reduces the number of planned road closures on the network. This has an impact on vehicle delays which also has an impact in terms of CO2 emissions from vehicles which are delayed through roadwork sites.
  • The HDM-4 model (Watanada, Harral, Paterson, Dhareshwar, Bhandari, & Tsunokawa, 1987), which was used in the VOC analysis also includes an emissions model, which is sensitive to the surface condition of the carriageway. Therefore changes in the carriageway surface condition (e.g. roughness) have an effect on the CO2 emissions from vehicles under normal operation.

It is important to note that vehicle efficiency is speed dependent, with optimal efficiency being achieved at the mid-speed range (around 80km/h or 50miles/h). On trunk roads reducing vehicle speeds (either as an effect of poorer carriageway condition or speed restrictions through maintenance sites) had the effect of producing a reduction in vehicle emissions. However, on the lower speed local road network delayed or slowed vehicles will generally emit more CO2.

No account was taken of improvements in engine efficiency through the analysis period. The efficiency improvement factors given by the Department for Transport (Department for Transport, 2011a) have been applied to the results from the HDM-4 analyses.

Further details of the emissions analysis are given in Appendix I, including results from the 8 sample Authorities. The results from Fife are shown in Figure 10.1 and Figure 10.2 for illustration.

The results for the analysis of emissions due to maintenance appear to follow a stepped relationship. This is a consequence of the availability of results for maintenance works in 3 or 4 year time steps preventing the presentation of a smoother year by year transition.

10.2 Local air quality

Local air quality is measured at various sites using specialised sampling equipment. The 'quality' of the air is determined by the concentrations of pollutants many of which are derived from the combustion of fossil fuels. Roadside air quality is site specific and predicting the change in air quality at any given site due to changes in maintenance funding is complex and outside the scope of a network level analysis. However, using the results of the network carbon emissions output from this study it has been possible, based on the typical combustion characteristics of the vehicle fleet, to determine the approximate increase in the mass of the combustion products which affect air quality. The full results of this analysis can be found in Appendix I and are summarised in Table 10.1.

Figure 10.1 Costs of emissions due to maintenance works - Fife
Embodied CO2 and vehicle emissions through roadwork sites. (2002 prices undiscounted)

Figure 10.1 Costs of emissions due to maintenance works - Fife

Figure 10.2 Costs of emissions from vehicles due to road roughness - Fife
(2002 prices undiscounted)

Figure 10.2 Costs of emissions from vehicles due to road roughness - Fife

Table 10.1 Emissions for all the Scottish local road network
Emission Scenario 1 (kg) Scenario 2 (kg) Scenario 3 (kg)
Nitric Oxide and Nitrogen Dioxide (NOx) 992.3 991.5 991.6
Particulate Matter < 10 µm (PM10) 85.4 85.3 85.3
Particulate Matter < 2.5 µm (PM2.5) 58.3 58.2 58.2
Hydrocarbons (HC) 188.9 188.8 188.8

There is little change in the emissions between the 3 Scenarios based on the assumptions made and the predicted changes in vehicle speeds.

10.3 Impacts of noise

10.3.1 Issues

Noise annoyance is defined by the World Health Organisation (WHO) as 'a feeling of displeasure evoked by noise'. The UK has well established procedures for assessing the nuisance to people caused by road and rail traffic-related noise and vibration. These procedures have been developed from surveys of the impacts of noise from transport on people, including dissatisfaction, annoyance and disturbance. More recently the Department for Transport commissioned a research study aimed at putting a monetary value on the impact of noise which is now captured in the analysis guidance (Department for Transport, 2011a).

According to Living Streets (Sinnett D. W., 2011) noise pollution particularly in towns and cities, can make conditions for walkers unpleasant at best and a health issue for some people. It can be a disincentive to walk close to or along main roads or in areas of stationary vehicles. It also states that noise makes casual conversation much more difficult. Thus, an increase in noise and vibration through a reduction in maintenance could have an impact on choices made by pedestrians and their way of life.

New road projects adopt the latest standards and often provide for noise mitigation measures such as noise barriers on urban freeways. These are not funded from the maintenance budget so the effects of changing the procedures for installing noise barriers have not been considered in this study.

The key area of expenditure in road maintenance which can have an impact on long term noise is road surfacings. The reduction in maintenance funding will reduce the amount of resurfacing and will lead to older surfacings lasting longer and pressure to adopt cheaper surfacing at the time of maintenance. After an initial settling in period (a few months), surfacings generally generate more noise with trafficking as they age. This may lead to a marginal impact on noise due to an ageing network. The difference in levels of noise from different surfacings has been explored for the Scottish local roads.

10.3.2 Assessment of Scottish context

Limited experience on Scottish local roads of potentially lower noise surfacings has been that they are of a similar final outturn cost and do not perform as well as other more traditional surfacings. This evidence from a recent TRL study for Scotland (Abbott, Morgan, & McKell, 2010) has again been confirmed with informal feedback during this study. Abbott looked at the experience of use of different surfacings and the potential benefits due to use of lower noise surfacings.

Key points derived from that study were:

  • Lower noise surfacings have the same initial costs or possibly slightly lower costs than more traditional surfacings. However, due to the shorter lives experienced to date, the whole of life costs for both options are similar
  • The extent of use of low noise surfacing on local roads is not accurately known and varies across Authorities. Some Authorities have used quieter surfacings extensively while others have had limited experience. Some Authorities have moved away from their use after poor experiences of performance
  • Low noise surfacings are now used reasonably extensively (around 25%) on the trunk road network

The study considered the whole of life economic costs of the two surfacing options, in both a rural and urban environment, and summary results of the comparison are shown in Table 10.2.

Table 10.2 Impacts of noise from different surfacings
Item Rural Urban
Road type Dual 2 lane Single 2 lane
Traffic level (veh/day) 24,000 8,000
Proportion heavy vehicles (%) 5 20
Initial cost (£/m2) 19.2 18.4 19.2 18.4
Expected life (yrs) 12 8 12 8
NPV [Works and user delay costs] (£k) 482 690 434 593
NPV [Works and user delays cf. HRA] (£k) Base 208 Base 159
NPV [Noise benefit] (£k) Base -3,431 Base -7,921

1. HRA = Hot Rolled Asphalt - the traditional UK surfacing

2. TSMA = Thin Stone Mastic Asphalt - the most common low noise surfacing option

Source: (Abbott, Morgan, & McKell, 2010)

The results of Table 10.2 are very dependent on the input assumptions in the examples. However, in summary, it shows there might be significant benefits from implementing noise reducing surfacings but that the works costs of such surfacings are higher in whole of life terms.

Given the limited experience to date of Local Authorities with lower noise surfacings, in the case of local roads it appears that any maintenance reductions will translate to a lost opportunity for realising any noise benefit, rather than an actual disbenefit.

For trunk roads, where there is already a reasonable proportion of the network with such surfacing in place, the conclusion is different to that for local roads. There could be a significant disbenefit if Transport Scotland shifts to using lower cost traditional surfacing as part of the implementation of lower levels of maintenance funding.