When hitting the road on the Wednesday before Thanksgiving or the Friday before Christmas—among the busiest days of the year—planning down to the hour can make a difference. With the help of Google Maps, we’ve charted the traffic patterns around four of the country’s biggest cities.

The data from Chicago, D.C., Los Angeles, and New York City reveal that on the Wednesday before Thanksgiving, 4 p.m. is the worst time to travel, while 5 p.m. is the worst time to travel on the Friday before Christmas.

Methodology: Google Maps analyzed the total number of cars on the road at a given time, looking at the speed of vehicles with location-services-enabled android smartphones. Traffic is measured for the year 2013.