Speed variation for different drivers, situations, and road geometry: Simulator and survey analysis

Drivers' speed selection has been a great interest to road safety researchers. In this study, a driving simulator (STISIM) was used to explore drivers' speed choices, and how they are influenced by infrastructure, traffic, risk/benefit, and driver characteristics. Drivers also filled out a stated-preference survey, which included speed selection items and demographic characteristics. The experimental design included four scenarios of a specific risk or benefit to the driver: A daily trip, a higher speed enforcement scenario, a higher crash-risk scenario, and a scenario with high time pressure. The driver sample included 111 drivers from different ages between 20 and 65, with 44% women. The database included 9,768 observations. The largest effect on drivers' speed was under time-saving benefits with an average increase of 10 km/hr. Infrastructure effects included horizontal curves, longitudinal slope changes, and design speed. Age and gender also influenced speed selection. Thus, the most effective measures for speed reduction may be (1) enforcement, (2) design speed, and (3) horizontal curves, in contrast to (1) time-saving benefits and (2) a high average speed of close-by vehicles, which motivated drivers to increase their speed but may be reduced by counteracting policies.