 DE 1 was first designated in the 1970s between Fenwick Island and US 113 in Milford , replacing a portion of DE 14 and following the newly constructed Milford Bypass . DE 14 between Fenwick Island and Milford had been built as a state highway in the 1920s and 1930s and was widened into a divided highway between the 1950s and 1970s . In the 1980s , a limited @-@ access Relief Route for US 13 was proposed between Dover and the Wilmington area in order to relieve that route of beach traffic . This relief route would be incorporated into DE 1 in 1988 , with the route extended up US 113 between Milford and Dover to connect to the Relief Route . The tolled DE 1 freeway between Dover Air Force Base and Christiana opened in multiple stages between 1991 and 2003 , and at a cost of $ 900 million was the largest public works project in Delaware history . The concurrent US 113 designation north of Milford was removed in 2004 . Upgrades continue to be made to DE 1 such as the construction and improvement of interchanges as well as widening portions of the road . 
