6 6 ▁runs ▁for ▁ ▁as ▁an ▁almost ▁entirely ▁a ▁north – s outh ▁und iv ided ▁surface ▁highway ▁in ▁western ▁Michigan ▁from ▁the ▁Indiana ▁state ▁line ▁north ▁to ▁Lake ▁Michigan ▁at ▁Char le vo ix . ▁Most ▁of ▁the ▁highway ▁is ▁two - lane ▁und iv ided ▁rural ▁highway . ▁There ▁is ▁a ▁section ▁south ▁of ▁Battle ▁Creek ▁that ▁is ▁a ▁four - lane ▁express way . ▁Running ▁north ▁into ▁the ▁C ere al ▁City , ▁M - 6 6 ▁is ▁concurrent ▁with ▁I - 1 9 4 , ▁which ▁is ▁a ▁full ▁fre ew ay . ▁This ▁section ▁along ▁I - 1 9 4 ▁is ▁listed ▁on ▁the ▁National ▁Highway ▁System ▁( N HS ), ▁a ▁system ▁of ▁high ways ▁important ▁to ▁the ▁nation ' s ▁economy , ▁defense , ▁and ▁mob ility . ▁Another ▁section ▁of ▁M - 6 6 ▁is ▁included ▁on ▁the ▁N HS ▁where ▁it ▁is ▁concurrent ▁with ▁either ▁M - 7 2 ▁or ▁U . S . ▁Highway ▁ 1 3 1 ▁( US   1 3 1 ) ▁in ▁K alk aska ▁or ▁An trim ▁count ies . ▁ ▁Indiana ▁to ▁I onia ▁M - 6 6 ▁is ▁a ▁four - lane ▁highway ▁that ▁connect s ▁with ▁State ▁Road ▁ 9 ▁( SR   9 ) ▁at ▁the ▁Indiana ▁state ▁line ▁in ▁southern ▁St . ▁Joseph ▁County . ▁The ▁highway ▁runs ▁north ▁to ▁St urg is ▁through ▁farm ▁land ▁where ▁it ▁turns ▁east ▁through ▁town ▁running ▁concurrent ly ▁with ▁US   1 2 ▁on ▁Chicago