EARLIER this week, councillors in Edinburgh voted to turn the capital into a "20mph city".

 

Under the plans, 80 per cent of of the city - including the entire city centre - will install blanket 20mph speed limits for drivers. Cue the inevitable jokes from the capital's congestion-weary motorists: "That fast, in Edinburgh?!"

Part of the rationale behind the scheme of course is to encourage people to get out of their cars and walk or cycle instead.

There are also hopes that it will cut the number of road traffic collisions.

Glasgow City Council is also pressing ahead plans to introduce 11 new 20mph zones in addition to the city's existing 54 existing low speed sites. Glasgow already has part-time 20mph zones around every school to safeguard pupils coming and going in the mornings and late afternoon.

The rollout in Edinburgh has not been without controversy, with opponents complaining that it will lengthen journey times, increase tailgating and deter trade.

Critics have also lambasted it as toothless, with the police admitting that it will not be routinely enforced and existing speed cameras unable to detect motorists exceeding 20mph.

In Brighton, the introduction of wall-to-wall 20mph zones engendered a sort of inverted Nimbyism. In essence, homeowners in Brighton were delighted to have a 20's plenty zone on their own doorstep when the council rolled them out across the town centre and residential streets in April 2013, but their support dwindled as soon as they drove much beyond their own neighbourhood.

That said, where 20mph zones have been widely implemented, researchers have noted a "cultural change" among drivers who begin to adapt and view travelling at 20mph as the norm even if they do not expect to be stopped by the police.

In fact, during the first nine months of the policy in Brighton not one driver was prosecuted for speeding - instead police cautioned or "spoke to" motorists caught exceeding the limit.

Nonetheless, figures published in August last year went on to reveal a 17 per cent decline in collisions and a 12 per cent drop in casualties in the areas where the 20mph zones had been introduced. In 2013/14 there were 54 fewer road traffic collisions compared to the three-year average of 318 from 2010-2013. Likewise there were 327 road casualties after the zones became live compared to an average of 371.7 during the three previous years.

Similar patterns have been noted in other studies. A paper published by the British Medical Journal found that between 1986 and 2006 in London, 20mph zones were associated with a 42 per cent reduction in casualties. In comparison, London as a whole experienced a 29 per cent reduction in casualties.

However, in other locations - such as Warrington and Middlesbrough - researchers found 20mph zones made "little or no significant difference" to collision and casualty rates.

As with a lot of research, the conclusion has been that "more data is needed" before 20mph zones can be declared a success or a damp squib.

Edinburgh will be Scotland's first major test case.