London's reputation as Britain's worst city for drivers may have to be revised, after a new study found that Belfast and Bristol suffer more from congestion.
Research from sat nav firm TomTom showed that typical journey times in the Northern Ireland capital were 32 per cent longer than they would be if traffic was moving freely.
This would turn a half-hour drive into a journey lasting 40 minutes.
Drivers in Bristol face similar delays: here, the busy roads mean trips take 31 per cent more time than they would in an ideal world.
Meanwhile in London, where a central congestion zone has been in effect since 2003, average delays are just 27 per cent.
Top 12 most congested cities in the UK
From most to least congested:
Unsurprisingly, the picture is significantly worse at peak times.
Belfast traffic moves 72 per cent more slowly during the morning and evening rush hours.
This means a motorist facing what should be a 45-minute commute would take more than an hour and a quarter to get to work.
This would result in a total of 141 extra hours every year being spent on the road as a result of high traffic volumes.
In Bristol, journeys take 56 per cent longer in rush hours – the same as in London.
Congestion across the UK
Other busy areas included the Leeds/Bradford conurbation, where average journeys take 26 per cent longer, Nottingham and Manchester (both 24 per cent).
TomTom compiled its Congestion Index from billions of pieces of data fed to it every day by users of its sat-nav devices all over the globe.
This allows the firm to calculate how long journeys should take when roads are clear and speed limits being observed.
And the information is then compared with actual journey times in 161 cities around the world.
The figures are regularly used to help local authorities plan their transport policy said the firm's head of traffic, Ralf-Peter Schafer.
"This detailed knowledge of the entire road network, helps businesses and governments make more informed decisions about how best to tackle and avoid congestion," Shafer said.
"Our traffic database contains over 6 trillion data measurements.
"This helps us determine which routes are the least busy and what times of day are best."
Congestion around the world
Motorists in Belfast and Bristol can take consolation they don't live in Moscow or Istanbul, to name two of the world's busiest cities according to TomTom.
Congestion in the Russian capital means an average trip takes 66 per cent longer than it should.
And journeys during the evening rush hour in Moscow are extended by a hugely frustrating 138 per cent.
In Istanbul, typical journey times are 55 per cent longer but 125 per cent longer in the evening.
Bad car day
The study also identified each city's most congested day of 2012 – with Thursdays and Fridays in the winter appearing to be the worst times to drive.
In Belfast the busiest day on the roads was Thursday 6 December.
In Bristol it was Friday 23 November and in London, Friday 19 October.
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