The 15 US cities with the absolute worst traffic

AP Photo/Jae C. Hong

Auto and tech companies are pouring money into car-sharing and autonomous driving as traffic becomes a bigger issue in cities.

It's such a problem that the average US commuter spends 42 hours stuck in traffic a year, according to a report by the Texas Transportation Institute.

TomTom, a navigation and mapping company, ranked US cities that have the most traffic congestion in its 2017 Traffic Index.

After collecting data over a nine-year time span, TomTom measured the extra travel time experienced by drivers over an entire year. TomTom assessed 189 cities overall and gave each a congestion score out of 100. Each percentage represents how much extra travel time it took on average to make any trip, anywhere in the city.

Here are the most congested cities in the US: