 Route 181 originated as an alignment of State Highway Route 6 @-@ A , a spur of State Highway Route 6 ( now U.S. Route 46 ) from Dover to Ross Corner . The designation was assigned in 1938 , eleven years after the then @-@ current highway system in New Jersey was started . The state highway route designation remained intact for fifteen years , until January 1 , 1953 , when the routes in state of New Jersey underwent a large renumbering . Route 6 @-@ A became Route 15 , running along NJ 181 's alignment from Jefferson to Sparta . The Sparta Bypass was constructed in 1974 , and upon completion , Route 15 was taken off of the Jefferson – Sparta alignment , which was re @-@ designated Route 181 . 
