How long can a semi-trailer be on all other roads?

Answer: B — 60 feet

Length limits for a semi-trailer depend on the road type. In Missouri, trailers are limited to 53 feet on interstates, but on all other roads the maximum is 60 feet. This distinction lets longer trailers be used where roads can accommodate them while keeping highway safety consistent. So the longest allowed semi-trailer on non-interstate roads is 60 feet. The 53-foot limit is for interstates, and 55 or 62 feet aren’t the standard limits in Missouri.