Speed limits on freeways vary, though many drive faster. Why?

Driving on the freeway in metro Detroit can spur a lot of questions: Why won’t they let me over? Who is honking? Where is my exit?

And on some area freeways, there is one ever-present question: If the speed limit is 55, why is everyone driving 80 mph?

The freeway system in metro Detroit is a complex set of arteries, built in pieces, responsible for moving millions of drivers every year at a variety of speeds. While some freeways, like the Lodge Freeway (M-10), say 55 mph is the limit, the Chrysler Freeway on the other side of Woodward posts 70 as the top speed.