Quantifying the effect of road design on urban road driving speed

Reducing driving speed is a key factor in improving road safety and combating noise emissions. As a result, an increasing number of cities worldwide are lowering speed limits on urban roads. However, main urban roads differ from residential streets in several ways, including their appearance, type of trips they accommodate, mix of vehicles and the presence of public transport. These differences limit the design options available for speed reduction. This paper examines the impact of continuous road design measures on drivers' preferred speed, safe speed and actual driving speed on urban main roads, as well as the psychological processes influencing these choices. A virtual reality (VR) study was conducted using a driving simulator. Participants drove through a series of main roads in VR with varying speed limits and road designs. Speed and lateral position were recorded; in a follow-up survey, participants stated their preferred - as well as the considered ‘safe’ - speed along different road designs. They were also asked about driving style, perceived complexity and safety of each treatment. Simulator results indicated that only specific road designs result in slightly lower driving speeds. Survey results revealed that certain measures influenced preferred and safe speed. Specifically, those with effectiveness linked to the presence or absence of other road users (cyclists, pedestrians, or other cars). Moreover, the study showed that perceived safety and complexity moderated the effectiveness of these road design measures. Overall, road design measures investigated in this study provided evidence on the impact of road design on driving behavior, but also demonstrated the need for further investigations to include dynamic human factors, as well as combinations of measures to achieve the goal of lower speeds on urban roads. • A VR driving simulator was used to study the impact of road design on chosen speed. • Complexity and risk perceptions influenced assessments of safe and preferred speed. • Continuous road design measures had only small effects on chosen speed. • Road designs with trees lowered driven speed; the presence of parking lowered preferred speed. • Combinations of human factors and multiple road design measures could be more effective.