 A road bearing the M @-@ 81 designation has existed since at least July 1 , 1919 , when the state initially numbered its trunkline highways . Since that time , it has been extended , rerouted or shortened several times . These changes resulted in essentially the modern highway routing by 1926 ; the highway was fully paved in the 1940s . A change made in 1929 was reversed in 1933 , and an extension through downtown Saginaw in the 1960s was overturned in the 1970s . The last change was the construction of a pair of roundabouts at the I @-@ 75 / US 23 interchange in 2006 . 
