Medical conditions as a contributing factor in crash causation Lindsay VLA and Baldock MRJ Centre for Automotive Safety Research, University of Adelaide, South Australia, Australia, 5005. email: tori@casr.adelaide.edu.au Abstract: Despite recognition that medical conditions contribute to the risk of crash involvement, little is understood about the mechanisms by which these conditions lead to drivers, riders and pedestrians being involved in motor vehicle collisions. This study involved in-depth at-scene investigation of 298 road crashes in the Adelaide metropolitan area in which at least one person was transported to hospital or fatally injured as a result of injuries sustained in the crash. Medical records for those attending hospital or undergoing post-mortem examination were checked for medical documentation providing evidence that a medical condition was a contributing factor in the crash. This information was then matched with the information gathered at-scene and during personal interviews to determine the extent to which the medical condition contributed to the crash, taking into account other factors. We found that almost half the drivers, riders and pedestrians (referred to as active participants) involved in the crashes had at least one pre-existing medical condition, and half of these individuals had two or more such conditions. Importantly, we found that a medical condition was the main causal factor in 13% of the casualty crashes investigated and accounted for 23% of all hospital admission and fatal crash outcomes. The findings highlight the role of medical conditions as a contributing factor in crash causation based on real crash data. Key Words: Medical conditions, crash causation, in-depth crash investigation, fitness to drive Introduction Impairment as a result of medical conditions and the role that impairment takes in crash causation have long been recognised as important road safety issues in Australia and other industrialised nations. Specific medical conditions identified as potentially placing drivers at risk include epilepsy [1], cardiovascular conditions [2], dementia [3], cerebrovascular accidents [4], diabetes [1], and eye conditions such as cataract [5] and glaucoma [6]. In addition to medical conditions themselves, medications taken to treat them can also place a driver at risk of a crash [7-8]. Furthermore, some drivers have multiple medical conditions and it may be that the combination of conditions compromises driving ability even when the individual manifestations of each of the separate conditions are minor [9]. It is also not only drivers who may be placed at the risk of a crash by the effects of a medical condition. A recent study by Gorrie et al [10] demonstrated links between older pedestrian fatalities and dementia. Although studies using licensing records or self-reports of volunteer samples have identified medical conditions associated with an increased risk of crashing, very few have actually involved consideration and examination of the crashes themselves. The presence of a medical condition for a driver or pedestrian does not suffice to claim that a crash was related to the condition in question. Often, many factors contribute to the occurrence of a crash and isolating the effect of a medical condition can be difficult [11- 13]. The primary aim of this study was to determine the proportion of casualty crashes that can be associated with the effects of a medical condition or an acute medical event (e.g. a seizure). The study involved the investigation of 298 casualty crashes occurring within metropolitan Adelaide, using a combination of data from a number of sources. These sources included evidence gathered from immediate examination of the crash scene, information obtained from follow-up structured interviews with crash participants, and information contained within hospital medical records. This detailed examination of the circumstances of This paper has been peer-reviewed November 2008, Adelaide, South Australia 2008 Australasian Road Safety Research, Policing and Education Conference 610