Travel Time Index (TTI): How slow traffic gets. The higher the number, the slower the traffic tends to get, compared to when the road is clear.
Daily Congested Hours: The total number of hours, per day, that traffic is significantly slowed
Thrillist Congestion Index (TCI): To figure out the total congestion index, we divided the total hours of daily congestion by the TTI, then multiplied that figure by the PTI, to give a true indication of how much time the traffic really does kill out of an average day.
Roughness (not shown): The International Roughness Index (yes, this actually exists) looks at road roughness by daily miles traveled. We weighted roads by how many miles they're driven each day, to account for real-world misery.