THE M4 could be widened and two new tunnels built under plans to ease congestion at one of its busiest spots.
The idea is among a series of options the Welsh Government is considering to ease traffic between junctions 23 and 29a - the exits for Magor and Castleton respectively.
Tailbacks are common along the busy 13-mile stretch of road, which "frequently exceeds capacity", and a report warns things could get worse in the future.
The Welsh Government has launched a consultation exercise about improving traffic flow on the stretch of road. Proposals on the table include widening the Brynglas tunnels, building a new dual carriageway and encouraging more people to use public transport.
Transport minister and Labour AM Carl Sargeant said: "Improving access to our schools, hospitals and workplaces is essential if we are to improve efficiency and productivity and, in turn, make us more competitive. I would urge people to share their views and experiences by taking part in this important consultation so we can ease the flow on the M4 and make this vital transport artery work better into the future."
Traffic problems between junctions 23 and 29a have been an issue for motorists and business for a number of years. Previously, blueprints for a tolled relief road were drawn up - but scrapped in 2009.
A year later, work on widening the carriageway between junction 32, which serves Cardiff, and junction 29, the western entrance to the Welsh capital, was completed - at a cost of around £50 million. The scheme was hailed a success - reducing congestion as well as accidents.
However, the Westward route going from the Severn Bridge towards Newport has continued to pose problems for many businesses, commuters and tourists - despite the introduction of a variable speed limit zone.
Among the new proposals is boring two new tunnels - expanding the carriageway to four lanes in each direction for nine miles. However, such a move is estimated to cost £550 million. Another proposal would see a dual carriageway being built to the south of Newport.
Officials said it would be "demand led" and "built in phases" and, unlike the originally-intended relief road, it would not be a motorway.