#13 Signalised intersection

Up to half of all road traffic crashes occur at intersections, which are characterised at the broadest level as either signalised or unsignalised.[1] The present summary focuses on signalised intersections which are, by definition, “controlled” intersections. While research shows human errors to be the main contributors to intersection crashes, infrastructure treatments and advanced vehicle technologies hold the key to intersection crash prevention and mitigation in a Safe System Approach.

Traffic lights

Controlling signalised intersections is typically achieved using traffic lights, which are programmed to facilitate efficient traffic movement by prioritising the highest volume traffic paths. From an operational perspective, this is clearly a logical traffic management approach. However, seeking to maximise network efficiency can necessitate a compromise between mobility and safety. A Safe System Approach attempts to minimise this trade-off through engineering and design features such as protected turns, speed reduction/management measures, and limiting the number of conflict points, among others. Further, while traffic lights are highly effective treatments for safety and network efficiency, red light running unfortunately remains a major contributing factor to intersection crashes. A range of supporting treatments may be used therefore to further improve signalised intersection safety, including:

Protected turns: dedicated turning lanes and associated turn signals are highly effective for reducing conflicts and represent the default position for signalised intersections in a safe system framework.

Speed management: Typical urban intersections involve travel paths intersecting at 90-degree angles, which is the most severe angle for side-impact collisions. The severity of such crashes increases significantly at impact speeds above 50km/h, yet many intersections have higher speed limits and drivers are unlikely to substantially reduce speeds mid-intersection upon detecting a hazard. Infrastructure treatments such as raised safety platforms and speed humps can help to improve intersection safety.  

Enforcement: Speed cameras and red-light enforcement cameras assist by encouraging compliance with speed limits and red traffic signals.

[1] Information sourced from Austroads Guide to Road Safety Part 2 and (US) FHWA “Intersection Safety”.