 A short stretch of MT 48 near what would become MT 1 existed by at least 1924 . By 1927 , a short , dirt , unimproved connector road existed near the location of MT 48 . By at least 1937 , that route had been paved , and connected U.S. Route 10 ( US 10 , now MT 1 ) to US 10S ( now I @-@ 90 ) . MT 48 was officially designated on May 16 , 1938 . By 1949 , all but 0 @.@ 046 miles ( 0 @.@ 074 km ) of MT 48 had been reconstructed along its current route . US 10 had been renumbered as US 10A by 1951 . Since then , both segments of US 10 have been redesignated and improved . In 1978 , the final 0 @.@ 046 miles ( 0 @.@ 074 km ) of the highway was reconstructed . MT 48 has not been worked on since . 
