Drivers may make errors that result in a collision with another vehicle, even when they are aware of the presence of the conflicting vehicle. This is because perceptual judgements about time, space, and speed are imperfect, and can lead to misjudgements about the adequacy of a situation to allow some driving manoeuvre. Drivers may err in thinking there is more time available for the manoeuvre than is actually the case; or err in thinking the manoeuvre takes less time to execute than it actually does. Either misperception could lead to a decision to go ahead with a manoeuvre with less margin of safety than the driver assumes. Misperceptions of the time available or time required for various driving manoeuvres under a range of conditions were studied in this project. In the laboratory experiment, research participants viewed video scenes, filmed from a driver's perspective, of a wide variety of situations. For each scene, the viewers made judgements about when some event would occur (e.g., approaching vehicle reaches them) or when some manoeuvre would be completed (e.g., own vehicle clears roadway when making a crossing manoeuvre). Participants' judgements were compared with actual values (for time available) or best estimates from engineering equations and empirical data (for time or distance required). A parallel on-the-road experiment, using similar procedures and a subset of the laboratory situations, was used to validate and benchmark the laboratory findings. The study found a general tendency for people to underestimate the time required to complete a manoeuvre. Across a range of manoeuvres, about 60% of all time or distance "required" judgements were underestimated, relative to engineering and empirical estimates. This misjudgement is safety-critical, because driver perception that a manoeuvre will take less time than is actually the case may lead to decisions to accept manoeuvre opportunities that actually afford a smaller margin of error than the driver perceives. Such misestimates were particularly common for judgements of the time to achieve the prevailing traffic speed during turning or merging manoeuvres, and for the time until one's vehicle reaches an intersection ahead. For judgements of the time "available" for a manoeuvre, the error was usually in a safety-conservative direction. That is, people felt they had less time than they actually did, so would be less likely to attempt a manoeuvre. However, even for time available judgements, there were meaningful numbers of safety-critical errors (overestimates of time available), especially for estimates of yellow signal phase time remaining and estimates related to a passing scenario. When the combined errors related to both manoeuvre requirements and availability were jointly considered, some situations emerged as particularly meriting consideration for safety countermeasures. These included: (1) approach to signalised intersections; (2) turns onto higher-speed roadways; (3) freeway merges; (4) passing; and (5) headway maintenance. Efforts were undertaken to development infrastructure-based countermeasure concepts. (Author/publisher)
Samenvatting