Some state routes built on freeway alignments may be upgraded to Interstate Highway standards ( or already built to Interstate standards ) and receive Interstate designation , such as the case with Pennsylvania Route 60 being largely replaced by I-376 . On the other hand , some routes are devolved to lower authorities , as with US 61 in Minnesota , which became Minnesota State Highway 61 from Duluth to the Canada – US border . At times , a state can abandon a number as the reason for state maintenance of the entire route no longer exists ; Arizona devolved the short Arizona State Route 62 to Mohave County government after a mine in Chloride closed and so did the economic purpose of the town . At the extreme a decommissioned route may be demolished , as was done with California State Route 480 . Once part of the Interstate Highway System , it required retrofitting to remain in service after the 1989 Loma Prieta earthquake to remain in use ; instead the highway was demolished
1989 Loma Prieta earthquake
1989 Loma Prieta earthquake
Decommissioned highway