Three auxiliary routes of Arkansas Highway 18 exist in Northeast Arkansas, with one former alignment.
Arkansas Highway 18 Spur is a spur route that runs to Newport Municipal Airport. The route is in length, and two-lane, undivided.
Arkansas Highway 18 Spur is a spur route in Jonesboro known as Dr. Martin Luther King Jr. Drive. The route is in length, connecting Highway 18 to I-555. Dr. Martin Luther King Jr. Drive is two-lane undivided. Its entire length is concurrent with U.S. Route 78 (US 78).
Arkansas Highway 18 Business is a business route in the small town of Manila. It connects US 78 and Highway 18 to Highway 77 (Beauchamp Street).
The Arkansas State Highway Commission created Highway 18B on March 7, 1962 from a former alignment of Highway 77 through downtown Manila. It was redesignated along another former alignment of Highway 77 on June 23, 1965, now running along West Lake Street.
Arkansas Highway 18 Spur is a former spur route between Leachville and Manila in Mississippi County, Arkansas.