 The highway turns westward along Wirtz Road and past the southern terminus of county road F @-@ 97 in the northern part of Gladwin County . Near a crossing with the Cedar River , M @-@ 18 turns north along Bard Road and then west again along Renas Road . The highway returns to its northerly course when it turns to run along Clarwin Road , which runs along the Clare – Gladwin county line . The roadway angles to the northwest briefly , cutting across the extreme northeast corner of Clare County as the highway crosses into Roscommon County . Through the southern portion of the county , the road runs through the Roscommon forest management unit of the Au Sable State Forest as it approaches Prudenville . In that community , M @-@ 18 turns northeasterly and runs along M @-@ 55 along the eastern shore of Houghton Lake . The two highways separate on the eastern edge of town , and M @-@ 18 turns northward , intersecting the northern end of M @-@ 157 . M @-@ 18 continues north , parallel to Interstate 75 ( I @-@ 75 ) near Higgins Lake ; M @-@ 18 crosses I @-@ 75 at exit 239 south of Roscommon . 
