Arkansas Highway 18 is a state highway of 20.4 miles (32.8 km) in Mississippi County.

AR 312 begins at AR 18 south of Blytheville. The route runs east cross over I-55, followed by a junction with US 61/AR 148. AR 148/AR 312 concur east until AR 312 turns north with AR 239. These two routes cross I-55 again heading north, with AR 312 eventually turning east alone as Promise Land Road.

AR 312 crosses I-55 for a third time before briefly joining with AR 151 heading north. The route then joins with AR 18 east, eventually turning due north to terminate at AR 150 near Number Nine.