Drivers in the city spend an average of 31 hours a year in traffic, according to the latest figures from traffic information website, INRIX
However, the number of hours drivers in Belfast spend in congestion has dropped by nearly eight hours in 2012.
All of the 18 UK cities analysed showed a decline in traffic congestion in 2012.
Bryan Mistele, chief executive officer, INRIX, said: "There has always been strong correlation between the state of the economy and the level of traffic congestion on our roads.
"It tells us if people are employed and driving to work, going out to eat or doing some shopping, as well as whether or not businesses are shipping products," he added.
"Considering unemployment hit record highs in 2012 and European household wealth dropped 13.6% to 10.9 trillion dollars (Â£7.13 trillion) , it is hardly surprising that traffic levels have dropped significantly."
Belfast is the sixth most congested city in the United Kingdom, according to a report published on Wednesday.