Work on the part west of I-805 and the I-5 interchange started in May 1984, with the construction of a detour for I-5; USACE paid for some of the costs, and federal funds related to the Interstate Highway System were also used. That same year, the county agreed to create a wildlife preserve on of marshland to resolve the environmental concerns. Meanwhile, the existing part of the South Bay Freeway had become the "most dangerous five-mile stretch of highway in the county", as declared by the local fire chief, due to the 282 traffic accidents that had occurred on the road from 1977 to January 1985. By early 1986, the extension of the SR 54 freeway to El Cajon was declared a "lower priority" by Caltrans.