Road traffic accidents in Singapore expressway tunnels

• Road traffic accidents that occurred on three expressway tunnels are studied.
• Accident rates are found to be highest in the transition zones.
• Accident rates are much higher in tunnel entry as compared to exit.
• Spatial differences in accident rates can be attributed to multivehicle crashes.
• Casualty likelihood is found to be higher in single vehicle crashes.

In rapidly growing economies with limited land space, underground road tunnels are becoming more prevalent. Before the implementation of large-scale underground road systems, it is necessary to garner more knowledge on their implications and impacts. This study examined 608 road traffic accidents (RTAs) that occurred in the three Singapore expressway tunnels, over 2009–2011. Each road tunnel was divided into three zones and RTA characteristics were analysed for each zone. The analyses reveal that RTA rates are higher in the transition zones compared to the interior zones, being mostly attributed to multivehicle crashes. However, mean casualty per RTA was found to be higher in the interior zones. Upon disaggregation by travel direction, it was found that RTAs are more likely to occur when entering the tunnel than exiting. The implications of the findings are discussed.