A smart motorway is a number of systems that work together to keep traffic flowing as smoothly as possible. They can be controlled (or automatically respond) to incidents and increases in traffic volume that would usually cause bottlenecks and traffic jams
What do smart motorways do?
- Open the hard shoulder as an extra lane to increase capacity
- Reduce the speed limit to keep all vehicles moving at the same speed
- Close a lane because of an obstruction
- Meter traffic onto the motorway using traffic lights on slip roads
- Display warnings or instructions to drivers, for example, to turn on headlights, not to overtake, etc
How do smart motorways control traffic?
- Sensors in the road and traffic controllers watching video feeds of traffic can decide to modify the system
- Prominent gantries over motorways display variable speed limits signs (if no speed limit is shown, it is 70mph)
- Each lane has a red X; if the red X is on, you must not use the lane otherwise you risk a fine and points on your licence.
- Slip roads have traffic lights around half way down to release vehicles at regular intervals rather than them bunching up and causing other traffic on the motorway to have to slow down
- Intelligent LED road studs (cat’s eyes) are beginning to be used which are more effective at directing drivers
- Eventually, smart motorways will communicate directly with smartphones to give real-time advice on alternative routes
What are the different types of smart motorway?
There are four types.
- Through junction running: this is hardly used now and is used to describe when a hard shoulder could be used before a junction to effectively lengthen the slip road off the motorway
- All lane running: Variable speed limits are used and the hard shoulder becomes a permanent lane. Gantry signs show speed and lane closures.
- Dynamic hard shoulder: Variable speed limits are used and the hard shoulder is used in some places to avoid congestion.
- Controlled motorways: Variable speed limits are used without the hard shoulder which is reserved for breakdowns and emergencies.
Are speed cameras active at all times?
Yes, even when variable signs are not active. Speed cameras also can be programmed to catch drivers exceeding a temporarily lower variable limit, e.g. 40mph. This can lead to some high fines if drivers see an essentially clear motorway and believe that the sign is ‘wrong’ and speed up to 70mph.