An annual global traffic report shows most cities’ average traffic speed fall last year, likely due to congestion factors.

The TomTom Traffic Index, which examined traffic conditions in 500 cities over 62 countries and six continents, its widest scope to date, found that 76% of cities’ overall average speeds fell year-over-year, though average speeds under optimal, free-flowing traffic were flat or slightly improved in most cities. It attributed the disparity to dynamic congestion patterns, including weather, rather than road infrastructure issues.

The index ranks the world’s slowest cities, putting Barranquilla, Colombia, as the slowest at an average travel time per six miles of about 35 minutes, or an average speed of 10.3 mph, followed by three cities in India. Rounding out the five slowest is London at just over 32 minutes, or 11.2 mph.

The most congested city, though, is Mexico City, with a congestion level of 52%.

Strikingly, no U.S. city, including Los Angeles and New York City, which just imposed congestion pricing on drivers this month, ranked high on various measures of bad traffic.

The index also ranks cities based on the most time lost due to rush-hour jams.

“The combination of population and economic growth is putting significant strain on our transportation networks,” said TomTom Vice President of Traffic Ralf-Peter Schäfer in a press release on the index.

“Outdated infrastructure and inefficient road planning fail to keep pace with demand. Additionally, the surge in e-commerce has led to a rise in freight traffic, further complicating the situation. Without a shift towards more regulation and sustainable transportation options, we risk worsening congestion that impacts everyone in our cities.”

LEARN MORE: Good News on Traffic Deaths