You might think that 30mph was chosen using scientific evidence but you would be wrong....

Back in 1934, just prior to the introduction of the 30mph speed limit, there were only around one-tenth of the cars on the road today, but four times as many associated deaths.

There had previously been a blanket 20mph speed limit, set in the 1903 Motor Car Act, but it was repealed for light vehicles in 1930. The spate of deaths caused a change of heart in government in 1934 and 1935, with 30mph brought in for built-up areas.

You might think that 30mph was chosen using scientific evidence but you would be wrong....

"It was pulled out of a hat," says Rod King, founder of the 20's Plenty for Us campaign, which believes that the 30mph limit today is no longer appropriate, credible or acceptable.

"The 30mph limit is compromised beyond belief," says King. Cities including London, Manchester, Birmingham, Bristol, Bath, Cambridge, Liverpool, Oxford, Brighton, Newcastle and Edinburgh, have introduced 20mph limits on some roads in their jurisdiction. The Lib Dems have even considered 10mph limits in some areas.

While motoring organisations the RAC and the AA have expressed support for 20mph limits outside schools, they oppose a blanket change from 30 to 20.

Today there are three typical speed limits across the UK:

• a 30mph limit on roads with street lighting (which is taken to indicate a built-up area)
• a 60mph national speed limit on single carriageways
• and a 70mph top speed on dual carriageways and motorways

The limits are meant to keep everybody safe. The Department for Transport (DfT) says that for every 1mph the average speed of vehicles reduces on roads, there are 6% fewer accidents.
Speed limits should be "evidence-led and self-explaining", the DfT explains, and "should be seen by drivers as the maximum speed rather than as a target speed at which to drive irrespective of conditions". Road safety in the UK is relatively good, with one death on the roads for every 20,000 cars.