Fewer than four in every 10 miles of A-roads in Renfrewshire are dualled, a new report has revealed.

Experts at the AA motoring organisation have said converting single-carriageway A-roads into dual-carriageways can "improve traffic flows and air quality whilst reducing collisions."

However, analysis of figures provided by the Department for Transport (DfT) shows only 39% of Renfrewshire's A-roads are currently dualled.

As dual-carriageways have extra lanes and a barrier between vehicles travelling in opposite directions, it is easier and safer for slower traffic to be overtaken.

Speed limits on dual-carriageways are up to 70mph, whereas single-carriageway roads can be no more than 60mph.

Edmund King, AA president, said: "The dualling of key A-roads greatly enhances connectivity and indeed road safety.

"Improving unsafe, congested, single-carriageway roads and building essential bypasses can improve traffic flows and air quality whilst reducing collisions.

"It is important to have a good network of connected and dualled A-roads, which are vital for the economy and environment.

"Congestion costs businesses billions of pounds and is detrimental to air quality and CO2 emissions."

Steve Gooding, director of motoring research charity the RAC Foundation, added: "For a whole array of financial and environmental reasons, it is implausible to think that we'll see a large-scale initiative anytime soon to dual our single-carriageway A-roads.

"A more practical and cost-effective answer to improving safety on A-roads is probably to 'engineer out' identified problems and hazards, rather than try to upgrade hundreds of miles of routes, with all that entails."

The DfT has said it is committed to reducing collisions and improving the roads network.

A spokeswoman added: "Our £24billion road strategy will ensure we have a network that is safe, reliable and well-maintained."