The state government began planning a major expansion of SR 539 to a four-lane highway in the late 1980s to accommodate local population growth and increased cross-border freight traffic. The corridor had been studied for widening in 1970 due to a high rate of fatalities compared to other rural highways in the state, but the projected traffic volumes did not justify expansion at the time. The highway was later identified as among the state's most dangerous, with 714 collisions and nine deaths from 1988 to 1993 and 314 collisions and three deaths from 1999 to 2003. The first phase of the project, covering between Horton Road in Bellingham to Ten Mile Road near Laurel, was approved for design work in 1999.