The TomTom Traffic Index is based on 19 trillion data points collected over nine years from 390 cities, according to the Dutch company.

Each city's congestion level was given a percentage score out of 100, with levels ranging from 66% in the most congested cities to 9% in the least.

TomTom defined the congestion level as the "increase in overall traffic times when compared to a free flow situation (an uncongested situation)."

Ralf-Peter Schaefer, VP TomTom Traffic, said in a statement that the traffic index is "designed to help drivers, cities and transport planners to understand traffic congestion and, most importantly, how to reduce it."

25. London, UK (40%)

24. Taipei, Taiwan (40%)

23. Tianjin, China (41%)

22. Shanghai, China (41%)

21. St Petersburg, Russia (41%)

20. Kaohsiung, Taiwan (41%)

19. Buenos Aires, Argentina (42%)

18. Shijiazhuang, China (42%)

17. Santiago de Chile, Chile (43%)

16. Hangzhou, China (43%)

15. Shenzhen, China (44%)

14. Guangzhou, China (44%)

13. Moscow, Russia (44%)

12. Los Angeles, USA (45%)

11. Changsha, China (45%)

10. Beijing, China (46%)

9. Tainan, Taiwan (46%)

8. Rio de Janeiro, Brazil (47%)

7. Chengdu, China (47%)

6. Istanbul, Turkey (49%)

5. Bucharest, Romania (50%)

4. Chongqing, China (52%)

3. Jakarta, Indonesia (58%)

2. Bangkok, Thailand (61%)

1. Mexico City, Mexico (66%)