M-3 is a north–south state trunkline highway in the Detroit metropolitan area of the US state of Michigan. For most of its length, the trunkline is known as Gratiot Avenue . The trunkline starts in Downtown Detroit and runs through the city in a northeasterly direction along one of Detroit's five major avenues. The highway passes several historic landmarks and through an historic district. It also connects residential neighborhoods on the city's east side with suburbs in Macomb County and downtown.