Traffic is a growing problem in cities worldwide.

Some cities have taken steps to cut congestion. Among those is London, which puts a fee on most vehicles driving in a designated congestion charge zone. But others have yet to find a real solution.

TomTom, a navigation and mapping company, has ranked the European cities it says have the worst traffic. The company collected data over nine years and gave each city a congestion score out of 100. The annual score, most recently updated with 2016 data, shows how much extra travel time it takes to get around a particular city.

Scroll down to see which European cities have the worst traffic:

13. Naples, Italy, received a score of 33%, meaning it takes drivers 33% more travel time to get to their destination in the city. The score is 2 percentage points higher than its one from the year prior.

12. Cologne, Germany, edges out Naples with a score of 34%. That's a big jump from 2015's score of 30%.

11. Warsaw, Poland, secured a score of 37%, which is actually a 1-point improvement from 2015.

10. Athens, Greece, tied Warsaw with a score of 37%, but its congestion increased slightly since 2015.

9. Manchester, England, got a score of 38%, which is only a 1-point difference from the year prior.

8. Brussels got a score of 38%, a 3-point increase from the year before.

7. Paris also got a score of 38%, a 2-point increase from the year before.

The warning is the starkest yet about the impact of leaving the customs union and having to introduce customs declarations (Getty)

6. Rome is known to have a traffic issue. The city secured a high score of 40%, a 2-point increase from the year before.

5. Marseille, France, got a score of 40%, a 2-point increase from 2015.

4. London has made an effort to cut traffic with a congestion pricing system, but it still has bad congestion. It secured a score of 40%, a 2-point increase from the year before.

3. Saint Petersburg, Russia, received a score of 41%, a 1-point uptick from the year prior.

2. Moscow got the same score as it did in 2015: 44%. Despite the city's major traffic issues, TomTom gave the city its parking award.

“Moscow's drivers have benefited from the implementation of a new intelligent transport system initiative, combined with major changes in parking policy, including pricing and enforcement,” TomTom said on its website. “These changes have reduced search time for a parking space by 65%.”

1. Bucharest, Romania, has the worst traffic in Europe, with a score of 50%, a massive 7-point increase from the year before.