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Eighty drivers in four groups of 20 (10 males; 10 females), aged under 30 years, 40–59, 60–69, and 70 years and over respectively, participated in a study, carried out in 1994 in the Waikato region, New Zealand, to identify factors contributing to crashes at rural T-intersections involving older drivers.

Laboratory-based tests involved tests of vision, memory, reaction time, and neck articulation. Drivers aged over 59 years had most visual defects and the poorest neck articulation. Participants in road-side tests, using a test vehicle parked at a right-angle to the highway simulating a T-intersection, were then asked to estimate the safe gaps and speeds for traffic approaching from their right. Safe gaps for a right turn onto the highway were estimated using threshold (last possible moment) and signal detection procedures (go/not go). A laser device recorded actual traffic speed and distance. The time taken by each participant to turn right across the road was also tested in a driving test.

Participants in all age groups judged speed poorly, over-estimating slower traffic and under-estimating faster traffic. They used distance rather than speed in gap estimation. While those aged 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 speed of approaching traffic exceeds 100 km/h, because of their failure to detect approaching vehicles, their poor estimation of speed and available gaps once vehicles are detected, and their slower lane clearance when turning. A range of countermeasures is suggested.

Keywords: Accidents, driver, driver age, driving, driving behaviour, gap acceptance, New Zealand, older driver, roads, rural, T-intersection, traffic, traffic accidents