The government is being urged to “get cars off the road”, as traffic in Britain returns to levels seen before the coronavirus lockdown.
Between 87% and 105% of the usual amount of vehicle journeys for the time of year have happened in the past two weeks, official figures show.
The Lib Dems said it was time to “fundamentally” rethink transport and the Greens warned of “gridlock”.
But a drivers’ rights group said busy roads were a sign of economic recovery.
The Association of British Drivers added that many people were using cars because they were still “nervous” about getting infected on trains and buses.
Boris Johnson has promised a “green recovery” from the cornavirus pandemic.
Last month, the prime minister said £2bn would be spent on encouraging walking and cycling, as part of an effort to improve health and fitness, and build on changes in transport use during lockdown.
In April, after restrictions on movement were imposed, journeys in motor vehicles dropped to 23% of the usual level in Britain. They have steadily increased since then.
But cycling surged in popularity during lockdown, hitting a peak of almost four times the usual level over the May Bank Holiday weekend.
This has since declined, but is still well above the average, with critics of the government saying it must do more to get people on to bikes.
Liberal Democrat environment spokeswoman Wera Hobhouse said: “The Covid crisis created an opportunity to fundamentally rethink how we use our road networks, but the government failed to be radical enough to deliver permanent change.
“Breathing fresher air and having more space on the roads for cycling was, for many, the only silver lining of the Covid-19 lockdown.”
She added that “to get cars off the road, local authorities need to be given the power and the resources to adapt road layouts to create distinct cycle lanes, separating cyclists from traffic”.
For Labour, shadow environment minister Ruth Jones said it was “concerning” that pollution levels were rising.
She called for an “urgent” inquiry into the “combined impact of air pollution and Covid on black, Asian and minority ethnic communities”.
Across Britain, around a quarter of the usual number of train journeys are happening at the moment.
For bus journeys, about half the normal amount are happening in London, and about two-fifths elsewhere in Britain.
Green Party transport spokesperson Caroline Russell said: “Public transport capacity is still much reduced from normal with the ongoing need to stay physically apart.
“If just a fraction of the people who usually catch the bus or train get into a car these traffic levels will quickly result in gridlock and a pollution spike, so it’s crucial local authorities help people make local journeys on foot and by bike.”
The government is trialling the use of rental electronic scooters, which it says could reduce urban road congestion in a way that “allows for social distancing”.
Roads into Devon and Cornwall are expected to be gridlocked for much of the weekend, with tourists arriving in their tens of thousands and bad weather forecast.
Association of British Drivers spokesman Roger Lawson said: “Everybody wants quieter roads, including drivers, but we disagree on how to do it.
“In many places putting in cycle lanes has squeezed traffic and made congestion worse. There’s been no provision for better roads, which would ease things.”
The AA said that, despite traffic returning to near-average levels overall, the situation was “far from normal” because more people were holidaying in Britain during the pandemic.
“The key question is what happens when the kids go back to school?” a spokesman said.
The Department for Transport was approached for a comment.