Sustrans Cymru - an organisation that promotes greener transport - has condemned the potential M4 Toll as "poor value for money".
A spokesman said that a "more cost effective way to reduce congestion would be to invest in shifting these journeys to public transport."
"The Welsh Government acknowledges that 40% of journeys on this stretch of the M4 are local trips of under 20 miles," he added.
More top news
The Trussell Trust said its network distributed more than 1.3 million three-day food supplies in the year to March.
The statue of the suffragist holding a banner reading ‘Courage calls for courage everywhere’ will be the first of a woman in Parliament Squa
A judge has said doctors at Alder Hey Children’s Hospital could stop providing life-support treatment to the 23-month-old.