▁Michigan . ▁Origin ally ▁ending ▁at ▁F ife ▁Lake ▁on ▁the ▁north ▁end , ▁the ▁highway ▁was ▁extended ▁to ▁Pet os key ▁in ▁the ▁late ▁ 1 9 3 0 s . ▁Further ▁changes ▁were ▁made , ▁starting ▁in ▁the ▁ 1 9 5 0 s , ▁to ▁convert ▁segments ▁of ▁the ▁road ▁to ▁a ▁full ▁fre ew ay . ▁The ▁state ▁started ▁this ▁conversion ▁simultaneously ▁at ▁two ▁locations : ▁heading ▁north ▁from ▁Three ▁R ivers , ▁and ▁heading ▁both ▁north ▁and ▁south ▁from ▁a ▁point ▁in ▁southern ▁Kent ▁County . ▁A ▁third ▁segment ▁was ▁built ▁south ▁of ▁Cad illa c ▁and ▁over ▁subsequent ▁years ▁Michigan ▁filled ▁the ▁g aps ▁in ▁the ▁fre ew ay . ▁Cad illa c ▁and ▁M anton ▁were ▁by pass ed ▁in ▁the ▁early ▁part ▁of ▁the ▁ 2 1 st ▁century , ▁resulting ▁in ▁the ▁current ▁fre ew ay ▁configuration . ▁Another ▁large - scale ▁construction ▁project ▁in ▁ 2 0 0 0 ▁re built ▁an ▁unusual ▁section ▁of ▁the ▁fre ew ay ▁through ▁Grand ▁Rap ids ▁known ▁as ▁the ▁S - Cur ve . ▁Two ▁brid ges ▁formerly ▁used ▁by ▁US   1 3 1 ▁have ▁been ▁l abeled ▁by ▁the ▁Michigan ▁Department ▁of ▁Transport ation ▁( MD OT ) ▁as ▁historic ▁structures ; ▁one ▁of ▁them ▁has ▁been ▁listed ▁on ▁the ▁National ▁Register ▁of ▁Historic ▁Places ▁( NR HP ). ▁ ▁Pl ans ▁to ▁further ▁extend ▁the ▁fre ew ay ▁have ▁either ▁been ▁can ce led ▁or ▁placed ▁back ▁under ▁study . ▁Up gr ades