How much have congestion warning systems contributed to crash prevention?


Congestion warning systems have a (slightly) positive effect on driving speeds and crashes. This conclusion is based on explorative research; further research is needed.

Congestion warning systems are mainly roadside systems and include Automatic Incident Detection (AID, better known as the matrix panels over motorway lanes) and Dynamic Route Information Panels (DRIPs), which are Variable Message Signs (VMS) informing drivers and alerting them to a traffic jam, incident or dangerous situation in downstream traffic. Such systems make use of current traffic data (obtained from induction loops cut into the road surface). When congestion is imminent, the matrix panels on the road portals display lower advisory speeds, with or without flashing warning lights. In case of incidents (crashes, spilled cargo, vehicle breakdown etc), a RWS incident protocol takes effect which alerts the relevant (emergency) services. On roads with traffic signalling (MTM) a red cross will appear above and next to the incident lane. If necessary, the road inspector will demarcate the incident and traffic will be controlled (via DRIPs and/or on-site).

Literature reviews of the effect of dynamic speed limits (via matrix panels)conclude that they have a positive effect on driving speeds and crashes [17]. This conclusion is indicative and requires further research. Research into the effect of DRIPs – that only inform drivers about the situation on the road – shows varying effects on road safety [18]. Some studies show a strong positive effect when DRIPs have been activated, compared to when they have not. Yet, little difference was found in crash patterns and crash numbers between locations with or without DRIPs. De Ceunynck & Focant [18] conclude that the use of DRIPs may have a positive effect on crashes, particularly because they positively affect driving speed.

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Traffic congestion and roadworks

Traffic congestion occurs when traffic demand exceeds road capacity, or when an incident such as a traffic crash, a vehicle breakdown occurs or Meer

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