Drivers with traumatic brain injury (TBI) may be impaired in their ability to predict other road users’ behaviour in order to anticipate traffic hazards. Slower anticipation of hazards has been associated with higher crash rates, but this driving skill has never previously been assessed after TBI. Three major questions were addressed: the impact of TBI severity on hazard perception, the impact of injury mechanism on hazard perception, and driving intentions following mild TBI (MTBI).
A validated and reliable hazard perception test (HPT) was used in all studies. Participants watched genuine, un-staged traffic scenes filmed from the driver’s point of view and were required to use a computer mouse to click on any road users they anticipated as causing a ‘traffic conflict’ (defined as situations in which a collision or near collision between the camera car and another road user would eventually occur). The main measure was participants’ mean response time to the traffic conflicts.
The aim of Study 1 was to examine the effect of TBI of all severities on hazard perception. Thirty-one drivers with TBI were recruited from a rehabilitation unit and 24 age-matched controls were recruited from the general community. Participants with TBI were slower to anticipate traffic hazards than controls. Within the TBI group, HPT response times were positively correlated with duration of post-traumatic amnesia, and participants with a complicated MTBI had faster HPT response times than participants with moderate to severe TBI. Therefore, hazard perception was found to be adversely affected by TBI. Moreover, the more severe the TBI, the more adversely affected hazard perception was.
The effect of MTBI on hazard perception was investigated in Study 2. Forty-two patients with MTBI and 43 patients with orthopaedic injuries were recruited from an emergency department within 24 hours of injury. Participants with MTBI were slower to anticipate traffic hazards than the controls. Study 2 provided the first indication that MTBI is associated with impairment in a safety-critical driving skill.
Study 3 was a more comprehensive investigation of the effect of injury severity on hazard perception. In addition, injury mechanism was analysed. Thus, the aim of Study 3 was to investigate the effect of mild head injury and high-force orthopaedic injury on hazard perception, and to determine whether indices of injury severity related to hazard perception performance. One hundred and eighteen patients with mild head injury, 43 patients with high-force orthopaedic injury, and 121 controls with low-force orthopaedic injury were recruited from an emergency department within 24 hours of injury. Participants with mild head injury were slower to anticipate traffic hazards than participants with low-force orthopaedic injury, but no other group differences were statistically significant. Within the mild head injury group, depth of post-traumatic amnesia was associated with slower HPT response times. Together, Study 3’s findings demonstrated that, within 24 hours of injury, individuals with mild head injury performed worse on a task critical to driving safely, and that the degree of impairment was directly related to the depth of post-traumatic amnesia.
The purpose of Study 4 was to describe the intentions of individuals recovering from MTBI regarding return-to-driving. Knowledge of the intention to return to driving in individuals with MTBI could determine whether there is a need to educate drivers who have recently sustained MTBI. Eighty-one patients with MTBI were recruited from a hospital’s emergency department. They completed an 11-item questionnaire measuring expectations regarding recovery from injury in which five of the items addressed return-to-driving. Only 48% of the sample intended to reduce their driving following their injury. However, those who did intend to reduce their driving nominated a mean duration of 16.59 days of reduced exposure. A logistic regression found that previous head injury experience and an interaction between pain and previous head injury experience predicted intentions to reduce driving. Similarly, a multiple regression revealed that pain level contributed significantly to the variance in time estimates of return-to-driving. HPT response times did not predict intentions to reduce driving. The finding that half the individuals recovering from MTBI did not intend to moderate their driving exposure post-injury is cause for concern, as Studies 2 and 3 have shown that driving performance is compromised in this group immediately after injury.
In summary, this research project showed that individuals with TBI and MTBI were slower to anticipate traffic hazards than appropriate control groups. Also, studies showed a relationship between severity of TBI as determined by PTA duration (Study 1) or depth (Study 3) and hazard perception. Although these preliminary findings signal the need for further research, hazard perception testing and training should be considered as part of driving rehabilitation after TBI. The link between MTBI and impaired hazard perception might warrant consideration of a policy advising individuals who present to the emergency department with MTBI to refrain from driving for at least 24 hours after injury.