Key 2007 Road Accident Statistics

10. Sources and definitions

10.1 The sources of the data

The figures in this bulletin were compiled from the "Stats 19" statistical returns made by police forces. These cover all accidents in which a vehicle is involved that occur on roads (including footways) and result in personal injury, if they become known to the police. As noted in section 3.2, there could be many non-fatal injury accidents which are not reported by the public to the police, and are therefore not counted in these statistics because the police can only include in their returns details of the accidents of which they are aware. More information about this is given in "Road Accidents Scotland 2006", in the section entitled "Comparison of the police 'Stats 19' road casualty figures with some other figures for Scotland". The vehicle(s) involved in the accident need not be moving, and need not be in collision - for example, the returns include accidents involving people alighting from buses. "Damage only" accidents (i.e. accidents which do not involve personal injury) are not included in these statistics.

10.2 The definition of "severity" used in the Road Accident statistics

The classification of the severity of an accident (as "fatal", "serious" or "slight") is determined by the severity of the injury to the most severely injured casualty. The police usually record this information soon after the accident occurs. However, if further information becomes available which would alter the classification (for example, if a person dies within 30 days of the accident, as a result of the injuries sustained in the accident) the police change the initial classification of the severity.

For the purposes of the Road Accidents statistical returns:

• a fatal injury is one which causes death less than 30 days after the accident;
• a fatal accident is an accident in which at least one person is fatally injured;
• a serious injury is one which does not cause death less than 30 days after the accident, and which is in one (or more) of the following categories:

(a)an injury for which a person is detained in hospital as an in-patient

or (b)any of the following injuries (whether or not the person is detained in hospital):fractures, concussion, internal injuries, crushings, severe cuts and lacerations, severe general shock requiring treatment

or (c)any injury causing death 30 or more days after the accident;

• a serious accident is one in which at least one person is seriously injured, but no-one suffers a fatal injury;
• a "slight" injury is any injury which is neither "fatal" nor "serious" - for example, a sprain, bruise or cut which is not judged to be severe, or slight shock requiring roadside attention;
• a "slight" accident is one in which at least one person suffers "slight" injuries, but no-one is seriously injured, or fatally injured.

Over the years, improvements in vehicle design, and the provision and use of additional safety features, together with changes in the law (e.g. on the fitting and wearing of seat belts), will all have helped to reduce the severity of the injuries suffered in some accidents. Road safety measures should also have reduced the levels of injuries sustained. For example, if traffic calming schemes reduce average speeds, people may suffer only "slight injury" in collisions that previously would have taken place at higher speeds and so might previously have resulted in "serious injury".

However, it is also possible that some of the changes shown in the statistics of "serious injuries" and "slight injuries" may be due to changes in administrative practices, which may have altered the proportion of accidents which is categorised as "serious". For example, the distinction between "serious" and "slight" injuries could be affected by factors such as changes in hospitals' admission policies. All else being equal, the number of "serious injury" cases would rise, and the number of "slight injury" cases would fall, if it became standard procedure for a hospital to keep in overnight, for precautionary reasons, casualties with a particular type of injury. The increase in the number of "serious" injury accidents in 1994 was partly attributed to a change in the health boards' policies in admitting more child casualties for overnight observation, which in turn changed the classification of many injuries from "slight" to "serious". The number of child casualties recorded as having serious injuries in 1994 was 35% higher than in the previous year. There could also be changes in hospitals' procedures that would reduce the numbers of "serious injury" cases. In addition, there is anecdotal evidence that changes in procedures for assigning severity codes may affect the categorisation of injuries. For example, different severity codes might be assigned by a police officer who was at the scene of an accident and by a clerk who bases the code on a police officer's written description of the accident.

10.3 Some other definitions

Built-up roads: accidents which occur on "built-up" roads are those which occur on roads which have speed limits of up to 40 miles per hour ( ignoring temporary speed limits on roads for which the normal speed limit is over 40mph).

Children: people under 16 years old.

Pedestrians: includes people riding toy cycles on the footway, people pushing bicycles, occupants of prams or wheelchairs, and people who alight safely from vehicles and are subsequently injured.

10.4 The targets for reducing road accident casualties by the year 2010

In March 2000, the UK Government, the then Scottish Executive and the National Assembly for Wales announced a new national road safety strategy and casualty reduction targets for 2010. These targets were introduced to focus on achieving a further substantial improvement in road safety over the next ten years, with particular emphasis on child casualties. The targets, which are given in the document "Tomorrow's roads - safer for everyone", are based on the annual average casualty levels over the period 1994 to 1998.By 2010 it is hoped that there will be, compared with the average for 1994-98:

• a 40% reduction in the number of people killed or seriously injured in road accidents.
• a 50% reduction in the number of children killed or seriously injured; and
• a 10% reduction in the slight casualty rate, expressed as the number of people slightly injured per 100 million vehicle kilometres.

10.5 The calculation of the "indicative lines" shown in the graphs

One way of assessing progress towards these targets is to compare actual casualty numbers in each year with an indicative line that starts at the baseline figure in 1996 and falls, by a constant percentage reduction in each subsequent year, to the target for 2010. This is the approach adopted by the GB Road Safety Advisory Panel. The indicative line starts at the baseline figure in 1996 because that is the middle year of the 1994-98 "baseline" period. Other approaches could have been used: there are many ways of producing lines that indicate how casualty numbers might fall fairly steadily to the targets for 2010.

In the charts on page 8, the thick solid lines show the figures recorded so far, the horizontal dashed lines show the baseline averages, and the dotted downward lines indicate how the figures would have to fall if the targets for 2010 were to be achieved by means of a constant percentage reduction in each year. They imply the following reductions from the 1994-98 averages by 2006:

Killed or seriously injured: 33.1%

Child killed or seriously injured: 42.0%

Slight casualty rate (per 100 million vehicle-km): 7.9%

- therefore, any falls which are greater than these suggest more rapid progress than the relevant indicative lines.

As the method adopted to produce the indicative lines involves a constant percentage reduction in each year, the lines are not straight. This is due to the "compounding over the years" effect of constant annual percentage reductions: each year's fall in an indicative line's figure is calculated by applying a constant percentage reduction to the line's number of casualties in the previous year (which reduces each year, so the falls between one year and the next get smaller and smaller). To two decimal places, the falls are: 3.58% p.a. for killed or seriously injured casualties; 4.83% p.a. for child killed or seriously injured casualties; and 0.75% p.a. for the slight casualty rate. A table on page 50 of "Road Accidents Scotland 2006" shows the percentages of the baseline averages in each year which are represented by each of the indicative lines.