You still drive on the right in Missouri. It's not Australia or England. So what's this sign doing at the westbound exit from Interstate 44 onto Missouri 66 in Jasper County? Eastbound traffic at this point is directed onto a service road for the freeway. The Keep Left sign combined with the Wrong Way sign is intended to keep eastbound traffic from driving into the westbound exit.
Photo courtesy of David Backlin (taken March 2004)