There are no state routes which duplicate an existing U.S. or Interstate highway in Ohio.

Ohio distinguishes between "state routes", which are all the routes on ODOT's system, and "state highways", which are the roads on the state route system which ODOT maintains, i.e. those outside municipalities,[2] with a special provision for Interstate Highways.

ODOT permits business routes but only "where an ODOT-maintained highway has been constructed on a new alignment which bypasses the CBD [central business district] of a municipality and no other ODOT-maintained highway provides a direct two-way connection between the bypass route and the CBD, or where the existing guide signing does not adequately direct the driver from the bypass route to the CBD and back to the bypass route.

[5] Main Market Roads, the most important of the system, were defined on April 15, 1913.

[citation needed] In 1935 the Ohio General Assembly passed a law which added 5,000 miles of roads to the state highway system over a 12-month period.