Question to the Department for Transport:

To ask the Secretary of State for Transport, what the criteria are for activating an average speed monitored stretch of motorway; what measures are in place to (a) prevent an artificially low speed limit being implemented and (b) ensure that an average speed limit camera check is in place for no longer than necessary; and if he will make a statement.

Average speed cameras are only used on motorways through roadworks for the safety of those travelling and working on the road. These limits are normally set at 50mph in accordance with published standards and in agreement with the police. Highways England can increase this speed limit to 55 mph or 60 mph where it is safe to do so. These speed restrictions are lifted once the roadworks are completed.

Highways England uses variable speed limits on smart motorways to manage traffic flows at busy times and in response to incidents on the network. A system of road sensors is used to detect actual vehicle speeds and the rate of flow of traffic on a motorway. Based on this information an algorithm is used to determine whether a reduced speed limit is required in order to maintain safety or optimise traffic flow. The algorithm works out the optimum speed for traffic by comparing the observed vehicle speed and traffic flow against the historical norm for a particular stretch of road. The automated system then activates the reduced speed limit at a level that will maintain safety and allow traffic to flow as freely as possible. Speed limits are set to 40mph to maintain safety when a slow moving or stopped vehicle is detected and are set to 50 or 60 mph to optimise traffic flow based on a number of factors detected by the sensors, including average speed, flow rate and traffic density.

The algorithm ensures that speed limits are returned to 70 mph as soon as the detected traffic parameters indicate that this can be done safely. Highways England traffic operations staff are also able to activate or deactivate variable speed limits manually based on observed traffic patterns should this be required.

These measures ensure that automated variable speed limits are set appropriately and that variable speed limits do not remain in place for longer than is necessary.

Highways England routinely monitors, reviews and learns lessons on the performance of variable speed limits on smart motorway schemes to ensure that the speed limits that are set are appropriate for the traffic conditions.