A major accident occurred on March 5, 1983, when a collision involving a patrol car and another car with three Secret Service agents inside occurred, killing all three Secret Service agents. This was due to the unusual curve that the road takes on near the end of its course in Mariposa County, created in order to support the hills of the Sierra Nevada. The patrol car was hired for a visit that Queen Elizabeth II was planning to Yosemite National Park in March 1983.