Ageing and Driver Behaviour at Rural T-Intersections

Eighty drivers in four groups of 20 (10 males; 10 females), respectively aged under 30 years, 40-59, 60-69 and 70 years and over, participated in research to identify factors contributing to older driver's rural T-intersection accidents. Participants estimated safe gaps and speeds for traffic approaching from their right from a test vehicle parked at a right-angle to the highway, simulating a T-intersection. Safe gaps for a right turn onto the highway were estimated using threshold (last possible moment) and single judgement procedures (go/not go). A laser device recorded traffic speed and distance. Each participant's speed at turning right across the road also was tested. Drivers aged over 59 years had most visual defects and the poorest neck articulation. All participants judged speed poorly, over-estimating slower, and under-estimating faster, traffic. They used distance rather than speed in gap estimation. While those under 30 years allowed the smallest gaps, those over 59 years were the least consistent judges and were slower to clear the next lane when turning right. Older drivers may be at higher risk at intersections, especially when approaching traffic exceeds 100kin/h, through failure to detect approaching vehicles, poor speed and gap estimation once vehicles are detected, and slower lane clearance when turning. Road safety research data identify intersections as major road crash sites. The rate of urban accidents is higher but the sequelae are more serious in rural settings because of higher speeds. Older drivers are over represented in the intersection crash statistics and 67% of older drivers who have crashes do so at these sites (Bernhoft, 1990; Evans, 1991; Frith, 1991). Typically, those accidents are multi-vehicle and side-on, frequently, they are fatal (Evans, 1988). Older drivers have more physical and sensory deficits, affecting their detection, perception and response to approaching vehicles. For example, their peripheral and monocular vision is more likely to be impaired and their ability to make compensatory head and/or body movements often is limited, so that early detection of, and response to, approaching vehicles is greatly reduced (Isler, Parsonson & Hansson, 1997; Klein, 1991; Owsley, Ball, Sloane, Roenker & Bruni, 1991). They often underestimate both the speed of approaching vehicles and the time needed to complete the turn safely (Hills, 1980). Major-minor road intersections present drivers with complex information-processing and motor tasks, as they have to identify and respond to signs, lane markings, and approaching traffic as well as slow down and stop, give signals, and make directional changes, all in an appropriate sequence. Concern over a pattern of fatal crashes involving older drivers at rural T-intersections in New Zealand under otherwise good driving conditions led Transit New Zealand (now known as Transfund New Zealand), the statutory body with responsibility for the country's major road system, to contract the present authors to investigate driver behaviour, especially gap estimation, at these junctions (for full sample description and detailed data analysis see Parsonson, Isler & Hansson, 1996) Method Eighty drivers participated, comprising 10 males and 10 females in each of four age groups, `young' (under 30 years, mean age M= 23.4), `middle aged' (40 to 59 years, M= 49.9); `older' (60 to 69 years, M=65.3); `oldest' (and 70 years and over, M=76.1). Pretests included a driving history questionnaire, a range of vision tests, including monocular visual acuity, stereovision, and horizontal peripheral vision (using a Keystone VS-II Vision Screener and perimetry), reaction time, degrees of head rotation, short-term memory, and a practical test of lane clearance in a right turn from a stopped position. Judgements of safe gaps and traffic approach speeds were made at a roadside site, simulating a T-intersection on a rural two-lane major road, by drivers seated in the research vehicle as if preparing to turn right onto the major road. …