The Big Question: Will reduced speed limits across Britain improve road safety?

Why are speed limits in the news?

The Department for Transport has announced the first major overhaul of speed limits since 1993. It is asking councils in England to review the limits imposed on all roads in their areas - including A, B and unclassified routes - to see whether they need amending. Similar instructions are also about to be sent out to traffic authorities in Scotland and Wales by their devolved administrations.

The new guidance does not affect motorways or the major A-roads, for which the Highways Agency takes responsibility. The Department wants any changes implemented within five years, but anticipates that many would take place much sooner than that. Stephen Ladyman, the Transport Minister, says he is encouraging lower limits where evidence warrants it but that authorities should consider increasing limits if it can be done safely.

What are the rules and how could they change?

England is criss-crossed by a road network of almost 300,000km, including 6,500 km of motorways and A-roads.

Originally there were no limits on motorways, but after a series of pile-ups in fog in the 1960s the limit of 70mph was introduced. The Government sets the overall framework for the speed limits across the country, but traffic authorities have the authority to vary them according to local conditions. Drivers are banned from exceeding 70mph on motorways and dual carriageways, 60mph on single carriageways and 30mph in built-up areas.

Ministers stress those limits will not be altered. The expectation is that councils in many areas will cut the limits from 60mph to 50mph or even 40mph on rural roads, where more than half of fatal accidents take place. More 20mph limits could be set in busy urban areas, although they could be eased to 40mph in quiet suburban areas.

The Government wants to address the confusion drivers can face on some rural roads, which have varying speed restrictions as they pass between different local authority areas. It also points out that many roads are now better designed and have been re-engineered - perhaps with traffic lights installed - since the limits were set. Councils are also being told to examine other ways of encouraging restraint by drivers. Suggestions include landscaping as well as "education, driver information, training and publicity".

Why does the Government back lower limits?

The Department of Transport insists it is not influencing local authorities in any particular direction and stresses that councils are free to allow higher speeds on roads in sparsely populated areas with good safety records.

But there is little doubt as to ministers' preference for lower limits - not least because the feel they could have a dramatic impact on the death toll on the nation's roads. Six years ago they set a target of cutting numbers of fatalities and serious injuries by 40% by the year 2010, rising to 50% among children. Research has discovered that each 1mph reduction in speed can cut the number of accidents by 5mph.

Are there environmental benefits?

Encouraging drivers to slow down would produce an environmental dividend. Cutting the speed limit on motorways to 60mph would reduce CO2 emissions by 18 per cent; simply enforcing the existing 70mph limit would cut them by 10 per cent. In 1994, the French Government enforced strict speed limits on main motorways and succeeded in reducing emissions by 19 per cent and accidents by 30 per cent.

Tony Blair's administration is reluctant to follow suit because of the expense and manpower involved. Ministers are also conscious of the fury they could face from motorists if more speed cameras were fitted. Their caution was lambasted this week by the Commons environmental audit select committee. It said: "Beyond its direct impact, a new policy on speed limits would help to raise awareness of the reality of climate change and of the need for everyone to take action on it."

How has the speed limit initiative been received?

Rural communities have complained that major roads passing through have become rat runs for motorists using them as alternative routes. It has therefore been enthusiastically welcomed by the Campaign to Protect Rural England. Sean Spiers, its chief executive, said: "There is a crying need for this and we know that lots of villages are lobbying their local authorities to introduce 30mph speed limits."

Both the RAC and the AA admit that speed limits need revising. Edmund King, of the RAC Foundation, said: "We do have some limits on A-roads, where there isn't pedestrian or cycle access, where the limit is 40mph, whereas in other cases they would be 60mph. But there are country roads going through villages where the limit is 60mph, when it should be 30mph."

Andrew Howard, the AA Motoring Trust's head of road safety, said: "In a rural context, no-one who lives in a country town would expect to have to drive 20 miles at 30mph to get to the next town. "On the flip side, people who live on a narrow road from a village to a hamlet would not expect to have cars doing 60mph on it."

So will motorists' behaviour change?

Anyone who has been in the slow lane of the motorway doing a steady 70mph watching a procession of cars rush past knows what a tall order that could be. And many police forces have historically turned a blind eye to modest speed violations. But that has changed in the era of speed cameras and drivers have found it easier to pile up penalty points. Even Mr Ladyman once accumulated nine points for speeding offences. Today he says he is a "sinner who repenteth" and that his experiences changed the way he behaves behind the wheel of his red Alfa Romeo GT.

There is evidence that behaviour can change over time. Attitudes to drinking and driving have been transformed and wearing a seatbelt - once regarded as nanny state meddling - has become second nature. To force British motorists to drive more slowly will be more challenging. It could require tougher action by police, courts and ministers.

Should driving speed limits be lowered?

Yes...

* Numbers of deaths and serious accidents - particularly among children - could be cut substantially

* CO2 emissions would be lowered, helping to tackle global warming

* Villages and rural communities cursed by motorists racing along major A-roads would breathe a sigh of relief

No...

* Unreasonably low limits would fail to win the support of the instinctively law-abiding motorists

* With traffic congestion worsening in many parts of the country, lower limits could aggravate the problem

* Suspicions could be aroused that yet more speed cameras are being installed as an easy revenue-earner rather than safety device