A 50MPH speed limit could be imposed on the M4 near Newport in a move designed to ease crippling congestion.

It is one of several suggestions put to the Assembly by consultants hoping to solve the daily bottle-neck problems around the Brynglas Tunnels.

It is hoped the measures, which include junction improvements, better lighting, using the hard shoulder as an extra lane and a park-and-ride scheme along the M4, will provide short-term solutions before work begins on the planned £350 million M4 relief road, scheduled to be completed by 2012.

The relief road will link Junction 23A at Magor and Junction 29 at Castleton and run south of Newport.

Consultants from Capita Symonds, who wrote the report, suggested imposing the new speed limit on the stretch of road between junctions 24 and 28 but an Assembly spokesman refused to confirm this has been agreed. The spokesman for Economic Development and Transport Minister Andrew Davies said: "Some of the measures are in place already and some are yet to be decided on.

"Many of the schemes proposed, particularly the short and medium-term ones, will be implemented as soon as possible because they are designed to reduce congestion and in that way, aid the south Wales economy."

The Assembly spokesman said the cost of the measures was incorporated into the 15-year, £8 billion transport review announced last December.

The study"s authors believes that it could help improve traffic flows, reduce serious accidents due to sharp-braking, as well as bring some improvements in air quality for residents living nearby.

Improvements at the High Cross junction and chevron road markings to encourage cars to keep their distance are also being suggested.

An idea for a park-and-ride scheme which would involve providing express buses between strategic points along the M4 and also into Newport and Cardiff would need further feasibility studies, according to consultants.

The Making Better Use study was commissioned in 2002 for the Assembly government.

Work is due to begin on the relief road in 2010. The road, which is likely to be tolled, faces opposition from environmental groups.