Traditionally a motorway had 3 lanes of live traffic and a hard shoulder. With a predicted 60% increase in traffic by 2040, the Government has been forced to look at how best to increase capacity without widening the road.
This has led to the introduction of Smart Motorways, the first of which was successfully trialled on the M42 in 2006 with the opening up of the hard shoulder to traffic at times of peak congestion.
There are now 3 types of Smart Motorways (previously known as Managed Motorways) in operation in England. These are:
Dynamic hard shoulder running
This involves opening the hard shoulder as a running lane to traffic at busy periods to ease congestion. This system is in operation on the M42, M1, M6, M4 and M5. Motorways with dynamic hard shoulder running have a solid white line; this differentiates the hard shoulder from the normal carriageway. This lane should NOT be used if a red X is displayed on the gantry sign above the lane. On a dynamic smart motorway the emergency refuges are spaced 500-800 meters apart.
All lane running
This type of Smart Motorway uses the hard shoulder as a permanent 'live' running lane for traffic and was first trialled on the M25. All running lanes have broken white lines, with the former hard shoulder lane only being closed in an emergency. On all running motorways the emergency refuges are spaced 2.5 km apart.
There is some debate as to whether All Lane Running is as safe as one with a permanent or temporary hard shoulder. Louise Ellman, Chair of the Transport Select Committee said on the 30th June 2016:
Highways England's analysis of the safety of smart motorways with all lanes running that incorporate the MIDAS queue protection system give a safety benefit (reduced risk of injury collisions) of about 19% compared with the baseline of a traditional dual 3-lane motorway with continuous hard shoulders. With MIDAS (Motorway Incident Detection and Automatic Signalling). Inductive loops detect the volume and speed of traffic and send data automatically to the local control centre and to overhead variable message gantries in the form of pre-set messages.