The effects of indicating rear-end collision risk via variable message signs on traffic behaviour

- Few studies investigate the effectiveness of safety messages on driving behaviour.
- Effects of risk messages regarding collisions on driving behaviour were measured.
- The same message may evoke opposite effects in different situations.
- Risky Behavioural adaptation was observed under low and medium risk messages at night.
- The effects of high risk messages were consistently related to safe adaptations.

Research on the effects of safety messages on driving behaviour remains relatively scant. The present study aims to manipulate drivers' risk perception by displaying messages containing risk level information, and measure the behavioural implications. Using proximal safety indicators (i.e. rear-end collision risk index), the risk level in each 5 min time interval was determined by traffic conditions in the previous 5 min interval based on a linguistic scale of “low”, “medium” and “high” risk. The risk level was displayed on Variable Message Signs (VMS) and changes in risk perception indicators (i.e. speed, time to collision and safety margin) were compared with null messages, while keeping other conditions similar in terms of driving lane and time (day/night). The experimental data set including about 43,000 vehicles was obtained by inductive loop detectors at one freeway site over two days. The control sample, where null messages were displayed, included about 40,000 vehicles and was also obtained at the same location using the same method on two different days. Results suggest that the same message may evoke opposite effects in different situations. Risky behavioural adaptations were observed under low and medium risk messages during night time. The effects of high risk messages, however, were consistently related to safe adaptations. The effects of messaging on rear-end conflicts were significant only in the fast lane at night time. The results could be used in regulating the activation algorithm for safety messages in real time VMS.