The Impact of Intersection Design on the Driving Performance of Adults in the Recovery Phase of a Turn

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Occupational therapy and other researchers in the United States (US), United Kingdom (UK), Europe and Australia have found that age-related changes and the greater likelihood of multiple chronic diseases put older drivers at an increased risk for unsafe driving behaviours or crashes (Mollenkopf et al 2002, Di Stefano and Macdonald 2005, Mitchell 2008, Classen et al 2009). Although people, 65 years and older, are living longer and driving longer (Foley et al 2002, Mollenkopf et al 2002, Mitchell 2008), the predictability of on-road driving performance is still under investigation, making the identification of at-risk drivers difficult (Insurance Institute for Highway Safety [IIHS] 2003). Apart from these person and measurement complexities, the safety of older drivers is also challenged by environmental features, such as roadway designs (Council and Zeeger 1992).

The US Federal Highway Administration (FHWA) proposed guidelines for highway design to increase the safe driving ability of older drivers (Staplin et al 2001). These guidelines include assessments and recommendations applicable to four categories of roadway design features: those appropriate for intersections, interchanges, roadway curvature /passing zones and construction work zones. In Britain, the comparable organisation to the FHWA is the Highways Agency. This is the public sector agency responsible for England's motorways and trunk (national) roads. Scotland and Wales have similar organisations, which fall under the devolved administrations for roads in their areas.

Although researchers examined, in a recent on-road study, the effect of intersection design (during the turn phase of an intersection) on the driving performance of older (65-85 years) and younger (25-45) drivers, little empirical evidence exists to support the effectiveness of the FHWA guidelines (Classen et al 2007). The present study deals exclusively with roadway intersection features in an urban area and presents the results from a follow-up study, examining the driving performance of young and older adults during the recovery phase of an intersection.

The researchers deemed this issue very important because (1) crashes and crash-related injuries and fatalities among older drivers are most prevalent in the northern and southern hemispheres at urban intersections; (2) despite the fact that road users in the UK drive on the left side of the road rather than the right side of the road as tested in this study, the outcome of environmental design may benefit drivers regardless of the side of the road they are driving on; and (3) the role of the environment on occupational performance is well articulated in models of the occupational therapy profession (Dunn et al 1994, Kielhofner 2002). As such, this study is in part conducted to inform occupational therapists about the potential benefits of environmental adaptation, specifically improved intersection design, as a facilitator for safer driving.


Characteristics and vehicle kinematics of driving manoeuvres at road intersections

Regardless of the side of the road that one is driving on, driving manoeuvres at intersections involve approach, turn and recovery phases. Using the FHWA guidelines (Staplin et al 2001) and an instrumented vehicle, an assessment was made (Classen et al 2007) of the turn phase at five pairs of improved and unimproved intersections. In general, this study showed that young and older adult participants alike benefited from roadways with safety features, suggesting that the FHWA guidelines are helpful for safer driving while making a turn for at least three of the five improved intersections studied.

After making a turn, a transitory action, the vehicle moves into the recovery phase. This phase is defined as starting at the end of the turn phase, where yaw (rotation about a vertical axis that passes through the car's centre of gravity and causing the car to swing off-course, also known as rate of turn) drops to a value of 0. …