A 50mph speed limit could be introduced on a 10-mile stretch of the M4 through Newport to ease congestion.
The M4 through Newport is seen as a bottleneck
A park-and-ride scheme and an uphill hard shoulder lane are other measures suggested by consultants.
They are included in a report, released by the Welsh Assembly Government, to look at improvements at the rush-hour bottle-neck.
They are seen as short-term solutions before work on a planned £350m M4 relief road starts.
The 50mph limit is suggested for the M4 between junctions 24 and 28, Coldra and Tredegar Park.
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.
Improved lighting, chevron road markings to encourage cars to keep their distance are also being suggested.
The Making Better Use study by Capita Symonds was commissioned in 2002 for the assembly government.
M4 IMPROVEMENT IDEAS
50mph speed limit, junctions 24-28
Better lighting, junctions 29-34
Park and ride
Improvements at High Cross junction
Hard shoulder climbing lane, jct 32 westbound
The park-and-ride scheme, which would be the most costly of the measures, would involve providing express buses between strategic points along the M4 and also into Newport and Cardiff.
It would need to involve a further feasibility study, says the report.
More radical ideas rejected included using hard shoulders for buses and closing junction 26 eastbound at Malpas and junction 25 at Caerleon.
Plans for a 14-mile relief road between Magor and Castleton - which is likely to be a toll motorway - were announced in late 2004.
But work would not start for five or six years and business leaders in south Wales have already expressed concern at the economic impact of congestion, around the Brynglas tunnels at Newport.
The relief road, between junctions 23 and 29, is expected to cost at least £350m and is likely to be tolled, but faces opposition from environmental groups.
Economic Transport Minister Andrew Davies said in December that work on the road, through the former Llanwern steelmaking site, could start in the next five years.
It is part of the assembly government's 15-year transport plan.