 M @-@ 18 is maintained by the Michigan Department of Transportation ( MDOT ) like all other state trunkline highways . As a part of these maintenance responsibilities , the department tracks the traffic volumes along the roads under its jurisdiction using a measurement called annual average daily traffic ( AADT ) . This is a metric for the level of traffic along a roadway segment for any average day of the year . In 2009 , MDOT calculated that 14 @,@ 017 vehicles used the section of M @-@ 18 along the M @-@ 61 concurrency , the highest traffic levels along M @-@ 18 . The lowest AADT was found along the highway in Crawford County in the 2009 surveys . Commercial traffic varied between the 50 trucks daily in Crawford County and the 214 trucks a day north of Gladwin . No section of M @-@ 18 has been listed on the National Highway System , a network of roads important to the country 's economy , defense , and mobility . 
