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Road Accidents Scotland 2003
2. Accidents
2.1 Accidents by road type and severity(see Table 4)
Table 4 shows separate figures for trunk roads and for local authority roads. Trunk roads accounted for only small proportions of the total numbers of accidents in 2003: 29% of fatal accidents, 18% of the total of fatal and serious accidents, and 15% of all accidents. The trunk road network's shares of accident numbers in previous years were broadly similar.
When looking at changes over time in the numbers of accidents by type of road, one must remember that the changes for different types of road will be affected by the transfer of traffic away from some roads by the opening of city and town bypasses, and by the construction of new roads with higher average traffic volumes. Therefore, such figures do not provide an accurate measure of the comparative change in the road safety performance of different types of road.
Several changes were made to the trunk road network with effect from 1st April 1996. Annex E refers to them, and explains why the 1994-98 averages for trunk roads and for local authority major roads have been calculated by counting accidents which occurred prior to 1st April 1996 on the basis of whether they occurred on roads which were part of the "post- 1 April 1996" trunk road network.
2.2 Accident rates(see Table 5)
Accident rates showing the number of accidents per 100 million vehicle kilometres are contained in parts (b) and (c) of table 5. These are calculated by dividing the numbers of accidents on each type of road by the estimated volumes of traffic on those roads, which were provided by the Department for Transport, and which are available for all types of road with effect from 1993. The "five year average" accident rates were calculated by dividing the total number of accidents which occurred in each five year period by the total of the estimated volumes of traffic for the same period, rather than by calculating the averages of the individual accident rates for the five years.
Accident rates have fallen markedly since the early 1990s. The overall fatal accident rate has dropped from 1.02 per 100 million vehicle kilometres in 1993 to 0.71 in 2003; the "fatal and serious" accident rate fell from 11.40 to 6.61; and the overall accident rate (all severities) reduced from 47.43 per 100 million vehicle kilometres to 33.02. Motorways had consistently lower accident rates than A roads. Leaving aside the relatively low rate for fatal accidents, minor roads (taken together as a group) tend to have higher accident rates than major roads, and accident rates tend to be higher for "built-up" roads (roads with speed limits of up to 40mph) than for "non built-up" roads (ones with higher speed limits).
Estimates for the total volume of traffic by police force area are now available for all roads back to 1993 on a consistent basis. Part (c) of the table shows that estimated accident rates vary considerably by police force area. Some of this variation may be attributed to the distribution of traffic by road type within individual areas.
2.3 Accidents by month by road type(see Table 6)
The numbers of injury accidents over the years 1999-2003 were fairly evenly spread throughout the year, with a minor peak in November, which was 13% above the average monthly number of accidents. Fatal and serious accidents (taken together) were similarly well spread across the months, and their minor peak, which occurred in August, was 12% above the monthly average. (To allow more equitable comparisons the months are standardised to 30 days.)
On average, there were 24 fatal accidents per month in the years 1999 to 2003. The number did not vary greatly between the months: the lowest average was 20, and the highest was 31.
2.4 Accidents by light condition and road surface condition(see Table 7)
The severity of accidents is associated with the light and road surface conditions, and also with whether the accident occurs on a built-up road or on a non built-up road. Perhaps, because of the higher average speeds on non built-up roads, severity rates are higher on non built-up roads than on built-up roads. And perhaps, because of poorer visibility, severity rates are higher in darkness than in daylight. For example, taking the annual averages for 1999-2003, 4.9% of injury road accidents on non built-up roads in darkness (76 out of 1,540) resulted in one (or more) deaths compared with 1.5% of accidents on built-up roads in darkness (40 out of 2,650) and 3.5% of accidents on non built-up roads in daylight (130 out of 3,738). Similarly, the percentage of accidents classified as either fatal or serious is higher for non built-up roads in darkness than for either built-up roads in darkness or non built-up roads in daylight.
Severity rates did not appear to be higher when the road surface condition was wet, damp or flooded, or affected by snow, frost or ice. For example, taking the annual averages for 1999 to 2003, the percentage of accidents on non built-up roads classified as fatal or serious when the road surface condition was dry was 30.5% (718 out of 2,352) compared with 25.8% (638 out of 2,471) when the surface was wet and 20.0% (83 out of 416) when it was affected by snow, frost or ice.
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