Michigan Highway 21 once ran from Holland to Port Huron, all the way across the state, but after a couple of trimmings, it now runs from Grand Rapids to Flint. Interstate 69 supplanted Michigan Highway 21 east of Flint; what's more, a deletion of the route in the Grand Rapids area led a western, severed former portion of the route to be renumbered as Michigan Highway 121. In the present day, Michigan Highway 21's western end is on the east side of Grand Rapids, at an intersection with Michigan Highway 44 that's very near Interstate 96. From there, Michigan Highway 21 heads east through Ionia, St. Johns, and Owosso. The eastern extent passes through downtown Flint to end just east of there. Interstate 475 catches the eastern end of the route, where the frontage roads, dubbed "Chavez Drive", provide full access to onramps and from offramps.
My photo of Michigan Highway 21 comes from Owosso, Michigan. Not many vehicles are heading west on Michigan Highway 21 to turn onto the southeasterly Michigan Highway 71, but nevertheless, a guide assembly shows those westbound drivers how and where to do that. That's the guide assembly shown in this photo. A trip around eastern Michigan, including Metro Detroit and the Thumb region, allowed me to snap this photo of Michigan Highway 21 in April 2021.