Traffic levels were up in Belfast yesterday morning compared to the same day last week.
Since lockdown was put into force in March the public has been urged to stay at home and only travel for essential purposes.
But data published by location technology firm TomTom showed there was more traffic across the UK's major cities compared with the previous week. The congestion level in London at 8am was 19%, up from 16% last week.
Other cities to experience an increase included Belfast, from 12% to 15%.
Birmingham was up from 9% to 11%; Cardiff from 8% to 11%; Edinburgh from 12% to 15%, and Manchester from 10% to 13%.
The figures represent the proportion of additional time required for journeys compared with free-flow conditions.
Anecdotal evidence suggests traffic levels here have been increasing gradually.
Meanwhile, there was a 10% increase in London Underground journeys early yesterday compared with the same period last week.
Demand between 5am and 6am was up compared with last week, but down from Wednesday.
People in England are being urged to return to work but avoid public transport.
Communities Secretary Robert Jenrick said he would be prepared to board a packed bus or train to commute to work as the coronavirus lockdown is eased, although he acknowledged overcrowding was a problem.
"We have given guidance that to protect yourself and others you could choose to wear a face covering," he said.
"You should be taking precautions like social distancing if you can.
"I appreciate that isn't always possible and some of the scenes... show buses and Tubes too full to be able to sit two metres apart, and that's a problem."