Accident Analysis and Prevention 32 (2000) 659 – 663 Motorcycle engine size and risk of moderate to fatal injury from a motorcycle crash John Langley a, *, Bernadette Mullin b , Rodney Jackson b , Robyn Norton b a Injury Preention Research Unit, Dunedin School of Medicine, Uniersity of Otago, PO Box 913, Dunedin, New Zealand b Department of Community Health, Injury Preention Research Centre, Uniersity of Auckland, Auckland, New Zealand Received 10 February 1999; received in revised form 14 July 1999; accepted 30 July 1999 Abstract Current New Zealand law requires that motorcyclists with a learner or restricted licence ride a motorcycle with an engine capacity of 250 cc or less. Previous research has reported inconsistent findings regarding the relationship between cubic capacity and risk of a crash. We sought to determine: (1) compliance with the law; (2) if the risk of an injury crash is increased for learner/restricted licence holders who do not comply with the cubic capacity regulations; and (3) whether the risk of an injury crash increases with increasing capacity of the motorcycle. A population-based case-control study was conducted in the Auckland region over a 3 year period from February 1993. Among the controls, 66% were riding motorcycles with a capacity greater than 250 cc. The percentages for those with: full, learner and restricted, and no licence were 82, 29 and 60%, respectively. There was no evidence that learner and restricted licence holders who did not comply with the cubic capacity requirement were at increased risk. It should be noted however, that 75% of those who were complying were doing so on motorcycles of 250 cc or less. Relative to motorcycles of less than 250 cc the risk of an injury crash was elevated by at least 50% for all cubic capacity categories, with the exception of the 251 – 499 group. There was, however, no consistent pattern of increasing risk as cubic capacity increased. The findings of this study coupled with the fact that cubic capacity is a poor measure of power suggest that, if cubic capacity was to remain the sole basis for restricting learner and restricted licence holders, consideration should be given to having a substantially lower cubic capacity than 250 cc. An analysis of risk in terms of power to weight ratio and style of motorcycle may provide a more useful insight into the benefits of motorcycle design restrictions for novice riders. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: Motorcycle; Cubic capacity; Crash www.elsevier.com/locate/aap 1. Introduction Motorcycle traffic crashes are a significant cause of motor vehicle traffic fatalities and injury in New Zealand (Langley et al., 1994). Moreover they con- tribute disproportionately to the road traffic problem. In 1990 it was estimated that motorcycles accounted for less than 2% of kilometres driven on public roads (Ministry of Transport, 1990), but in that year they accounted for 16% of the fatal motor vehicle traffic crashes (Land Transport, 1990) and 22% of motor vehicle traffic crashes resulting in hospital inpatient treatment (Department of Health, undated). Internationally licensing restrictions have been im- posed to reduce the injury burden from traffic crashes. A three stage Graduated Driver Licensing System (GDLS) comprising learner, restricted, and full licence was implemented in New Zealand in 1987. GDLS for car drivers is targeted at the 15–24 year age group. In contrast, those seeking a motorcycle drivers licence must complete all stages regardless of their age. The GDLS requires a driver with a restricted or learner licence to ride a motorcycle with a cubic capacity 250 cc or less. Similar restrictions apply in several other coun- tries, however, the scientific evidence to support these restrictions is limited. In 1984 the scientific literature on the relationship between engine size and collision involvement was re- viewed by Simpson and Mayhew and they concluded * Corresponding author. Tel.: +1-643-479-8511; fax: +1-643-479- 8337. E-mail address: john.langley@stonebow.otago.ac.nz (J. Langley) 0001-4575/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII:S0001-4575(99)00101-3