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Chapter Five Understanding the Impact of Long Distance Commuting on the Scottish Transport Network

Introduction

5.1. The Transport Model for Scotland ( TMfS) was used to assess, in detail, the impact of the current level of long distance commuting in Scotland (excluding the highlands) on traffic related matters.

Long distance commuting and contribution to traffic volumes.

5.2. Consideration was given to the contribution of long distance commuting to traffic volumes on the Scottish transport network. TMfS (base year 2002) provided estimates of absolute numbers of long distance commuters in the AM peak hour on each road link. Traffic volumes are illustrated in Figure 5.1 for all of TMfS area and Figure 5.2 for central Scotland. It may be seen from the figures that the highest volumes of long distance commuting traffic are on the key trunk road routes. (M8, M9/A9, Forth Road Bridge, M77/A77, M80, A92 etc)

5.3. In addition to consideration of absolute numbers, analysis involved the percentage of AM Peak traffic made up of long distance commuter traffic. Percentages of long distance commuters on each road link are illustrated in Figure 5.3 for all TMfS area and Figure 5.4 for central Scotland. It may be seen that the proportion of long distance commuting vehicles relative to other vehicles tends to be fairly low (often less than 20%) within the main urban areas, while inter-urban routes and key trunk roads have significant percentages (often exceeding 50%) of AM Peak traffic made up of long distance commuter traffic.

Long distance commuting and average vehicle speeds

5.4. Predicted changes in road speeds following the removal of long distance car commuters indicate that there would be a reduction in congestion levels during the AM Peak period. It may be seen from Table 5.1 that the average speed on all motorways would increase by 7km/hr In addition, the average speed on all trunk A-roads (with speed limits greater than 40mph) would increase by 4km/hr and on all trunk A-roads (with speed limits less than 40mph), the average speed would increase by 2km/hr

Table 5.1: Change in average speed by road type

5.5. Table 5.2 details the changes in Local Authority average AM Peak speed if all long distance work trips were removed from the transport network. The greatest average speed increases are predicted in Aberdeen City (25%), Glasgow City (11%) and Midlothian (10%).

Table 5.2: Change in Local Authority average speed by road type

*Not fully included within TMfS area

5.6. Figure 5.5 illustrates the predicted percentage change in vehicle speed on each road link in the AM Peak following the total removal of long distance commuters from the TMfS transport network. It may be seen that significant increases (often exceeding 50%) in AM Peak vehicle speed would be achieved within Edinburgh, Glasgow and Aberdeen city centres and on the Forth Road Bridge.

Long distance commuting and vehicle emissions

5.7. Quantification of vehicle emissions created by the long distance car-based commuter was estimated using TMfS. The impact of completely removing long distance commuters from the Scottish transport network is summarised below and the change in percentage contribution of pollutants is detailed in Table 5.3.

Table 5.3: Total annual AM emissions (Tonnes)

5.8. Vehicle emissions created by the long distance car-based commuter are detailed by Local Authority area in Table 5.4. It may be seen that Inverclyde, Aberdeenshire and East Lothian would see the greatest reductions in pollutants if long distance car commuting trips were removed from the transport network. For example, car long distance commuters are responsible for 56% of Carbon Monoxide pollutants in Inverclyde, 51% of Carbon Monoxide in Aberdeenshire and 50% in East Lothian.

Table 5.4: Percentage reduction in AM peak emissions by Local Authority Area

Figure 5.1: Long distance commuting: number of vehicles in AM peak - all TMfS area (2002)

Figure 5.2: Long distance commuting: number of vehicles in AM Peak - central Scotland (2002)

Figure 5.3: Long distance commuting: percentage of total AM peak traffic - TMfS area (2002)

Figure 5.4: Long distance commuting: percentage of total AM peak traffic - central Scotland (2002)

Figure 5.5: Percentage change in vehicle speed following the removal of long distance commuters - all TMfS area (2002)

Figure 5.6: Percentage change in vehicle speed following the removal of long distance commuters - central Scotland (2002)

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