 M @-@ 81 is maintained by the Michigan Department of Transportation ( MDOT ) like other state highways in Michigan . As a part of these maintenance responsibilities , the department tracks the volume of traffic that uses the roadways under its jurisdiction . These volumes are expressed using a metric called annual average daily traffic , which is a statistical calculation of the average daily number of vehicles on a segment of roadway . MDOT 's surveys in 2010 showed that the highest traffic levels along M @-@ 81 were the 17 @,@ 839 vehicles daily between Van Gelsen Road and Frank Street in Caro ; the lowest counts were the 3 @,@ 527 vehicles per day east of Cass City to the M @-@ 53 intersection . No sections of M @-@ 81 have been listed on the National Highway System , a network of roads important to the country 's economy , defense , and mobility . 
 M @-@ 81 is maintained by the Michigan Department of Transportation ( MDOT ) like other state highways in Michigan . As a part of these maintenance responsibilities , the department <a href='uninflect' title='1'><mark>tracks</mark></a> the volume of traffic <a href='null_relcl' title='2'><mark>that</mark></a><a href='uninflect' title='3'><mark>uses</mark></a> the roadways under its jurisdiction . These volumes are expressed using a metric called annual average daily traffic , which <a href='drop_aux' title='4'><mark>is</mark></a>a statistical calculation of the average daily number of vehicles on a segment of roadway . MDOT <a href='null_genetive' title='5'><mark>'s</mark></a>surveys in 2010 showed that the highest traffic levels along M @-@ 81 <a href='uninflect' title='6'><mark>were</mark></a> the 17 @,@ 839 vehicles daily between Van Gelsen Road and Frank Street in Caro ; the lowest counts <a href='uninflect' title='7'><mark>were</mark></a> the 3 @,@ 527 vehicles per day east of Cass City to the M @-@ 53 intersection . No sections of M @-@ 81 <a href='been_done' title='8'><mark>have</mark></a> been listed on the National Highway System , a network of roads important to the country <a href='null_genetive' title='9'><mark>'s</mark></a>economy , defense , and mobility . 
M @-@ 81 is maintained by the Michigan Department of Transportation ( MDOT ) like other state highways in Michigan . As a part of these maintenance responsibilities , the department track da volume of traffic use tdaroadways under its jurisdiction . These volumes are expressed using a metric called annual average daily traffic , which a statistical calculation of thdaverage daily number of vehicles on a segment of roadway . MDOT  surveys in 2010 showed that thedaghest traffic levels along M @-@ 81 was the da@,@ 839 vehicles daily between Van Gelsen Road and Frank Street in Caro ; the lowest counts was the 3 @,@ 527 vehicles per day east of Cass City to the M @-@ 53 intersection . No sections of M @-@ 81 done been listed on the Ndaonal Highway System , a network of roads important to the codary  economy , defense , and mobility .