▁of ▁White water , ▁where ▁a ▁new ▁by pass ▁has ▁been ▁constructed . ▁It ▁is ▁currently ▁two - lane , ▁but ▁can ▁be ▁expanded ▁to ▁four ▁lan es . ▁U . S . ▁ 1 2 ▁continues ▁west ▁to ▁Mad ison . ▁As ▁US ▁ 1 2 ▁ne ars ▁Mad ison , ▁it ▁mer ges ▁with ▁US ▁ 1 4 , ▁US ▁ 1 5 1 ▁and ▁US ▁ 1 8 , ▁to ▁form ▁the ▁West ▁B elt line ▁Highway , ▁a ▁four ▁to ▁six - lane ▁fre ew ay ▁that ▁enc ir cles ▁the ▁south ▁and ▁west ▁port ions ▁of ▁the ▁city , ▁with ▁a ▁speed ▁limit ▁of ▁. ▁ ▁From ▁Middle ton , ▁the ▁highway ▁continues , ▁on ▁a ▁, ▁four - lane ▁road ▁completed ▁in ▁ 2 0 0 4 , ▁to ▁cross ▁the ▁Wisconsin ▁River ▁at ▁Sau k ▁City . ▁ ▁Illinois ▁ ▁In ▁Illinois , ▁US ▁ 1 2 ▁is ▁an ▁ar ter ial ▁surface ▁road ▁that ▁runs ▁from ▁Richmond , ▁sout heast ▁to ▁Des ▁Pla ines . ▁It ▁then ▁turns ▁due ▁south , ▁continu ing ▁through ▁the ▁Chicago ▁metropol itan ▁area , ▁joining ▁with ▁U . S . ▁Route ▁ 4 5 . ▁In ▁Stone ▁Park , ▁U . S . ▁Route ▁ 2 0 ▁joins ▁U . S . ▁ 1 2 / 4 5 . ▁In ▁H ick ory ▁Hills , ▁U . S . ▁ 4 5 ▁continues ▁south , ▁while ▁U . S . ▁ 1 2 / 2 0 ▁runs ▁due ▁east