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
Ross Brennan, 28, conspired with Aarron Gledhill, 30, to import and sell powerful class A drugs to thousands of customers.
Pyongyang's foreign minister said Donald Trump's aggressive rhetoric is regarded as a legitimate "declaration of war".
Former congressman Anthony Weiner has been jailed over an underage sexting scandal which helped rock Hillary Clinton's election campaign.