Google maps marks data out of typical traffic for that day and time in the week, basically meaning that if on a Thursday, at 3 pm, there is a wait time reported of 2 hours, where there is typically a reported wait time of 30 minutes during that same weekday and time, then it is marked as above usual traffic (and there are other factors google marks data with - a larger range than just saying "above usual traffic").
You may be familiar with the interesting phenomenon where pizza locations near the Pentagon seem to get large spikes in traffic right before major events - a great example being the recent strikes on Iran, which also raised traffic significantly for nearby pizza shops. Using the Google Maps API, this process can be automated and visualized, as seen here.
