SR 4B begins at a quadrant roadway intersection with SR 4 (Dixie Highway) and Ross Road in eastern Fairfield. Here, the connector road is located in the northwest quadrant of the intersection. The route travels north as a divided four-lane road first crossing over a CSX railroad and intersecting Port Union Road. The next three intersections SR 4B has (from south to north: Symmes Road, Tylersville Road, and Hamilton–Mason Road) are superstreet intersections. The roadway briefly expands to three lanes in each direction between Symmes Road and Tylersville Road as it crosses over a Norfolk Southern railroad. This segment also features the Fairfield-Hamilton city boundary. After the Hamilton–Mason Road intersection, SR 4B comes to a diamond interchange with SR 129 (Butler County Veterans Highway). North of Princeton Road, the route shrinks to an undivided two-lane road, passes under an overpass carrying Milliken Road, and ends at a signalized intersection with SR 4. The entirety of SR 4B is included as a part of the National Highway System.