North of this freeway interchange, M-18 is also the route of Business Loop I-75 (BL I-75). The combined BL I-75/M-18 runs north near the Roscommon Conservation Airport and turns northeasterly into town. In the middle of Roscommon, BL I-75 turns northwest along Old 76 Road, and M-18 continues northeasterly across a line of the Lake State Railway. The highway continues independently to the northwest over the South Branch of the Au Sable River and out of town. It then turns due east along the Roscommon–Crawford county line. This section of the county line also forms the southern boundary of the Huron National Forest. M-18 curves to the northeast off the county line into the national forest territory where it meets F-97 for a second time. At this junction, F-97 merges with M-18 and the two roads run due north to a junction with M-72 west of Luzerne. At this intersection, F-97 continues north and M-18 terminates in rural Crawford County.