Motorcycle accidents: preliminary results of an in-depth case-study

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Motorcyclists have a poor safety record when compared to other road-user groups. Their killed and serious injury (KSI) rate in the UK per million vehicle kilometres is approximately twice that of pedal cyclists, and over 16 times that of car drivers/passengers. Motorcycles and mopeds make up less than 1% of vehicle traffic, but their riders suffer 14% of the total deaths and serious injuries on Britain's roads (DETR, 2000). Though changes in motorcycle training have contributed to a fall in the number of motorcyclist casualties in the early 1980s and mid-1990s, this trend has reversed in more recent years. Possible reasons for this include the increasing sales of mopeds and scooters, and the increasing numbers of older motorcyclists returning to the road on fairly powerful machines after a long break.

Motorcycle accidents also have somewhat different characteristics when compared with other vehicle groups. KSI casualties in the UK peak through the 20-39 rider age-bands, and motorcycles are over-represented in ROWV accidents, high-speed accidents involving running off the road on bends, and accidents that are related specifically to the sort of manoeuvres that motorcycles can perform, e.g. overtaking other traffic without crossing the centre line, or 'filtering' between lines of traffic. Preusser, Williams and Ulmer (1995) found that a subset of fatal motorcycle accidents with characteristics similar to these, accounted for around 85% of the total, in a sample of over 2,000 such accidents.

Mannering and Grodsky (1995) point out several reasons why the characteristics of motorcycle accidents differ from those of other vehicles. Firstly, they claim car drivers 'tend to be inattentive with regard to motorcyclists and have conditioned themselves to look only for other [cars] as possible collision dangers'. Motorcyclists themselves often repeat anecdotal stories of the car driver's 'sorry I didn't see you' explanation for collisions.

Secondly, Mannering and Grodsky (1995) also claim that motorcycle operation is typically a more complex task than car driving, requiring excellent motor skills, physical co-ordination and balance. Motorcycle riding can also involve counterintuitive skills, such as 'counter-steering, simultaneous application of [mechanically separate] front and rear brakes, and opening the throttle while negotiating turns'. Any impairment (for example, from medication or alcohol) would therefore more greatly affect a motorcyclist's risk of an accident when compared with a similar level of impairment while car driving. Soderstrom, Dischinger, Kerns and Trifillis (1999) have argued that, for this reason, legal blood alcohol levels should be lower for motorcyclists than the level set for other drivers in the USA.

Mannering and Grodsky (1995) also state that, because motorcycle riding is well known to be a dangerous activity, it 'may tend to attract risk-seeking individuals, in all age and socio-economic categories', which would have a corresponding effect on the total motorcycle accident figures. Some evidence of another aspect of risk-seeking among motorcyclists was found by Soderstrom et al. (1999) in their study of casualties at a US hospital's trauma centre. They discovered evidence that the use of illegal pharmaceuticals had declined markedly in car driver casualties over a 10-year period, but not among motorcycle rider casualties. In addition, the use of alcohol, cocaine and PCP was found to be higher among injured motorcyclists.

Lastly, Mannering and Grodsky (1995) point out that most motorcycles offer a substantially better performance when compared with cars, due mainly to their far higher power to weight ratio. The higher engine-capacity sports machines offered for sale in the USA and UK frequently boast acceleration speeds of 0-60mph in under three seconds. Mannering and Grodsky report that 'some motorcyclists cite as the primary reason for selling their sport bike the fact that they are unable to resist the temptation to ride at dangerous speeds'.

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