Figures released in the Assembly show that traffic volumes on all classes of road fell in 2006 — following years where the trend had been inexorably upwards.

Responding to a question from East Antrim MLA Ken Robinson, Regional Development Minister Conor Murphy said that the motorway network saw the greatest reduction in traffic — a fall of 2.54 per cent during 2006.

Traffic on B class roads was down 2 per cent and vehicles on trunk roads fell by 1.26 per cent. The smallest reduction was on A class roads where the fall was 0.19 per cent.

Roads Service said it believed the fall in traffic was largely down to drivers making alternative plans to avoid major roadworks on the motorway network.

The figures are estimates based on vehicle counts at 270 sites across Northern Ireland.

Andrew Howard, head of road safety at the AA, said he believed the figures for the rest of the UK showed similar falls in traffic.

“During July and August 2006 there were what was perceived to be very high prices for fuel,” he said.

“It was also believed at the time to have been a fairly poor summer – these two factors combined meant some people did not take a second holiday within the UK.

“There are also more people working from home and improving public transport in Northern Ireland would also have had an impact.”

Mr Howard said he believed that the current record fuel prices, if they remain for a long enough period, may force drivers to drastically rethink their travel plans.

“In the long term, if you are living in Armagh and working in Belfast, you may decide to relocate because of the expense involved in travelling to work every day,” he said.

Friends of the Earth transport campaigner Lisa Fagan said she was surprised by the fall in traffic.

“These figures are something of a conundrum because they buck the trend of recent years when we have seen traffic volumes rise relentlessly,” she said.

“It may be that carbon-conscious motorists are beginning to car-share and use improving public transport. Alas, I suspect that to avoid roadworks on the Westlink and elsewhere, motorists have switched to roads that are not monitored.

Mr Robinson said he was surprised at the decrease as traffic still seemed to be growing on major routes from his constituency into Belfast. He claimed roads had become saturated because Planning Service had allowed developers to build without insisting that they upgrade the road network to absorb the extra traffic.

“On the continent you see complete roads with storm water gullies and street lights – everything is in place before construction begins but here we build first, then worry about the roads,” he said.