Looking forward to safer HGVs: the impact of mirrors on driver reaction times

Heavy Goods Vehicle (HGV) collisions are responsible for a disproportionate number of urban vulnerable road user casualties (VRU – cyclists and pedestrians). Blind-spots to the front and side of HGVs can make it difficult (sometimes impossible) to detect close proximity VRUs and may be the cause of some collisions. The current solution to this problem is to provide additional mirrors that can allow the driver to see into the blind-spots. However, keeping track of many mirrors requires frequent off-road glances which can be difficult to execute during demanding driving situations. One suggestion is that driving safety could be improved by redesigning cabs in order to reduce/remove blind-spot regions, with the aim of reducing the need for mirrors, and increasing detection rates (and thereby reducing collisions). To examine whether mirrors delay driver responses we created a series of simulated driving tasks and tested regular car drivers and expert HGV drivers. First we measured baseline reaction times to objects appearing when not driving (‘Parked’). Participants then repeated the task whilst driving through a simulated town (primary driving tasks were steering, braking, and following directional signs): driving slowed reaction times to objects visible in mirrors but not to objects visible through the front windscreen. In a second experiment cognitive load was increased, this slowed RTs overall but did not alter the pattern of responses across windows and mirrors. Crucially, we demonstrate that the distribution of mirror RTs can be captured simply by the mirror’s spatial position (eccentricity). These findings provide robust evidence that drivers are slower reacting to objects only visible in eccentric mirrors compared to direct viewing through the front windscreen.