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<p>Typically, variable mandatory speed limits are set by an automated system in response to changes in the speed and flow of traffic, although the Highways Agency can set them manually if needed. Variable speed limits are used to control traffic at times of heavy congestion to improve traffic flow, or following an incident for safety reasons. They are also used to ensure the safety of road workers when cones are being set out.</p><p>This automated system is based on research undertaken to establish the optimum speeds for maximising traffic flow. The rules governing these speeds are set via algorithms which are calibrated according to traffic flow. The automation of the system ensures a rapid response and also consistency across the motorway network.</p><p>Highways Agency operators can also manually set signs and signals. To do this they must select an appropriate reason within the technology system, which will</p><p>automatically assign an appropriate speed for that incident. For example, an unconfirmed incident would generate 50 mph in all lanes but a lane closure would generate 40 mph speeds in the adjacent lanes to preserve safety. Again, this ensures consistency across regions.</p><p>Operators do have delegated authority to override a speed limit with a lower speed, if required for safety reasons such as reducing the likelihood of secondary collisions following an incident. This is governed by Highways Agency procedures and is only done at the request of a traffic officer or police officer at the scene, or if adverse driver behaviour is observed by CCTV.</p><p>Under these procedures, control centre operators must check the validity of both automatic and manual speed setting. If an operator becomes aware of a speed limit which is not credible or appropriate to traffic conditions, he or she should take immediate action to remove it.</p> |