Motorists increased their speeds on Bedford's main routes last year as coronavirus lockdown restrictions sparked a drop in traffic levels, figures reveal.
The RAC says some drivers across the country took advantage of the emptier roads to drive at "dangerous speeds", including in residential areas.
Department for Transport (DfT) data shows cars and light vans travelled at an average speed of 27.2mph on 'A' roads in Bedford last year.
That was up from 25.7mph in 2019 – a rise of 6 per cent.
The A5141 had the biggest rise in speeds, up 22 per cent to 16.4mph, followed by the A5134, up 15 per cent to 21.6mph.
This was caused by a steady increase in speeds following the imposing of Covid-19 stay-at-home restrictions in March last year, the DfT said.
Densely populated areas had the biggest rise in average speeds – up 13 per cent – compared to a 4 per cent rise on rural roads.
Simon Williams, RAC road safety spokesman, said the impact of the pandemic on the country's roads was "something of a double-edged sword".
He added: "On the one hand, fewer delays is positive and may well have led to an improvement in overall air quality, but on the flipside, we know that some drivers have taken advantage of quieter roads by driving at dangerous speeds.
"This has been a particular problem on 30mph roads in residential areas."
Mr Williams said it is important police forces continue to crackdown on excessive speeders and that there are consequences for their "totally unacceptable" actions.
The figures cover only 'A' roads, which account for around 10 per cent of England's highway network but carry around a third of all traffic.
Speeds were measured using samples of vehicles recorded at different times of the day.
The data also reveals the impact of quieter roads on delays along the country's A roads last year.
In Bedford, road users were held up 33.5 seconds per mile on average compared to the pace they would have made if travelling up to the speed limit in free-flowing conditions.
That was a decrease of 20 per cent compared to 2019.
The road with the biggest drop in delays was the A5141, with a 32 per cent fall in the average hold-up time.
The DfT said the average speed of motorists across the main road network, including motorways, stood at 61.8 mph last year – below the speed limits for the majority of roads where vehicles were recorded.
The department also said average speeds and delays are returning to pre-pandemic levels as Covid-19 restrictions continue to be eased.
But this has not been welcomed by environmental group Friends of the Earth, which now wants increased funding for public transport and cycle ways to keep people away from their cars.
Jenny Bates, a FotE campaigner, said: "There's a serious risk that the benefits to our health and environment that came with quieter roads are going to become a distant memory."