Road speed limits in the United Kingdom

[6] A report published in 2010 by the Department for Transport regarding Portsmouth City Council's 20 mph (32 km/h) speed limit on 255 miles (410 km) of the city's 272 miles (438 km) of roads found a small 1.3 mph (2.1 km/h) reduction in traffic speed and a small 8% increase in the number of serious accidents – neither of which were statistically significant – and a 21% reduction in the number of accidents.

[10] A report published in 2008 estimated that following the introduction of 20 mph (32 km/h) zones in London, a reduction of casualties by 45% and KSI by 57% occurred.

[12] Research carried out for the Department for Transport, to provide supporting evidence for Local Transport Note 1/11 on shared space, showed that in all of the ten shared space sites that were studied, that although they all had speed limits of 30 mph (48 km/h), that the average speeds on them was around 20 mph (32 km/h).

These can be changed in response to weather, traffic levels, time of day or for other reasons with the currently applicable speed limit displayed using an electronic road sign.

[15] Variable speed limits were introduced on some congested major routes as an element of controlled motorway techniques to improve traffic flows for given prevailing conditions.

[citation needed] Rarely, minimum speed limits are used, such as through the Mersey Tunnels, to maintain free flow and safe passage through otherwise hazardous or enclosed areas.

[18] Contrary to popular belief, there is no minimum speed limit on motorways, although certain classes of slow vehicles (as well as those of any class that cannot maintain 25 mph (40 km/h) on the level whilst unladen) are prohibited on safety grounds and drivers are expected to not cause unnecessary obstruction by driving unusually slowly.

[21] The 70 mph (113 km/h) limit on previously unrestricted roads was introduced in 1965 following a number of serious motorway accidents in fog earlier the same year.

[20] The Parliamentary Select Committee for Transport Safety published a report entitled 'The Ending the Scandal of Complacency' in 2007 which highlighted how casualty levels rise with increasing speed and recommended reducing speed limits on streets with high pedestrian populations and on dangerous rural roads.

"Travelling too fast for conditions" (but within the prevailing speed limit) was recorded as one of the contributory factors in a further 8% of all collisions (and 9% of all fatal, 9% of all serious and 8% of all slight accidents),[n 3] The UK government publishes Reported Road Casualties Great Britain (RRCGB) each year, based on road traffic casualties data (STATS19) reported to the police, which has been collected since 1949, and with additional data going back to 1926.

The 2009 edition also summarised the characteristics of speed related fatal collisions as typically occurring on unclassified rural 60 mph (97 km/h) speed limit roads, the driver being a male under the age of 30, with the collision types being head-on, lost control or cornering and the cause being loss of control whilst cornering or overtaking and the contributory factors being excess or inappropriate speed, loss of control, aggressive, careless or reckless behaviour or in a hurry.

In 2024 it emerged Conservative Party politicians in England had been running popular Facebook groups opposed to the 20 mph (32 km/h) speed limit in Wales.

The Locomotives Act 1865 (the 'Red Flag Act') reduced the speed limit to 4 mph (6.4 km/h) in the country and 2 mph (3.2 km/h) in towns and required a man with a red flag or lantern to walk 60 yd (55 m) ahead of each vehicle, and warn horse riders and horse drawn traffic of the approach of a self-propelled machine.

5. c. 50), created by Leslie Hore-Belisha, the then Minister of Transport, introduced a speed limit of 30 mph (48 km/h) in built-up areas for cars and motorcycles which came into effect on 18 March 1935.

[44] The definition of a built-up area was based on the presence of street lighting,[45] which had previously been mandated by the Public Health Act 1875.

[47] A 20 mph (32 km/h) night-time speed limit for built-up areas was introduced in 1940 as an attempt to halt the increase in the number of road casualties occurring during the World War II blackouts.

[53] Following a series of serious motorway multiple crashes in the fog in 1965, Tom Fraser, the then Minister of Transport, following consultations in early November with the police and with the National Road Safety Advisory Council (NRSAC), concluded that the crashes were caused by vehicles travelling too fast for the prevailing conditions.

[54] On 25 November 1965 the government announced that a temporary 30 mph (48 km/h) speed limit would be applied to sections of motorway (there were 350 mi (560 km) of it at that time) affected by fog, ice or snow and that a general maximum speed limit of 70 mph (113 km/h) would be applied to all otherwise unrestricted roads, including motorways, for a trial period of four months starting just before Christmas.

[22] The four-month trial 70 mph (113 km/h) speed limit on 100,000 mi (160,000 km) of previously unrestricted roads and motorways was introduced at noon on 22 December 1965.

[55] Also on that day, the power for the police to apply advisory speed limits of 30 mph (48 km/h) to motorways affected by bad weather was also introduced.

The advisory limit was activated by the use of flashing amber lights placed at 1 mi (1.6 km) intervals along the motorways.

[55] In April 1966 Barbara Castle, the new Minister of Transport, decided to extend the experimental 70 mph (113 km/h) limit for a further two months to allow the Road Research Laboratory (RRL) time to collect data as there was still no conclusive evidence of its effectiveness.

[56] In May 1966 Barbara Castle extended the experimental period by a further fifteen months to 3 September 1967 as "the case is not proven" but there were signs of crash rate reduction.

[60] On 22 December 1965, a temporary 70 mph (113 km/h) speed limit was introduced on previous unrestricted roads and motorways for 4 months.

[63] Due to the 1973 oil crisis, a temporary maximum national speed limit of 50 mph (80 km/h) for all roads, including motorways, was introduced on 8 December 1973.

[n 8] The Road Traffic Regulation Act, which was passed in 1984, includes legislation relating to speed limits.

[73] In March 2009 the Government consulted on reducing speed limits on rural roads (on which 52% of fatalities had occurred in the previous year) to 50 mph (80 km/h).

It explained that 'crashes were more likely on rural parts of the road network, upon most of which the national speed limit of 60 mph (97 km/h) applies'.

[74] In February 2010 the Department for Transport undertook a consultation to set a 65 mph (105 km/h) speed limit for all buses, minibuses and coaches with more than eight passenger seats.

[77] In 2022, the Welsh government passed a law to make 20 mph (32 km/h) the default speed limit for built up areas in an effort to reduce the risk of road accidents.