Drivers' impressions of front and rear gaps in queues

Drivers' opinions on, and perception of, gaps to a leading and a following car were studied in two field experiments. In study 1, the drivers indicated their opinion on adequate, critical and legal gap to a leading and a following car at 40 and 80 km/h. The results showed that drivers indicated longer front gaps than rear gaps in all conditions. In study 2, the drivers made judgements of distance to a leading and a following car when standing still and when travelling at 80 km/h. They were also asked to manoeuvre to a position in the middle between the leader and the follower. The results in study 2 revealed a perceptual bias in the driver when travelling at 80 km/h in that the drivers were closer to the follower when they thought they were in the middle between the leader and the follower. Gaps were generally underestimated and front gap was more underestimated than rear gap. The differences between opinions on gaps in the forward and the rearward directions could, partly, be explained by a perceptual bias in the driver. The bias should have a safety-promoting effect since it makes the driver more tolerant against short rear gaps than without the bias.