Historical Tour of old US 99
Five Mile Grade : Castaic
US 99 started its climb over the Liebre Mountains here. This grade is five miles long – hence the name. This section was completed in 1933 and widened to four lanes in 1948. Both sides of the highway once went on this side as evidenced by the Truck Escape Ramp further up. That ramp, constructed in 1958, was heavily used until January 20, 1970 when the new southbound lanes for I-5 were opened.
This segment of I-5 is very unusual as the northbound and southbound sides have been switched, sometimes called the “English Switch”. Northbound, which uses the old grade US 99 used, is west of the southbound lanes. A completely new roadway was built for the southbound lanes on a different ridge east of the old grade. This was done to create a shallower grade for downhill traffic. The old grade was 6%, whereas the new downhill grade is only 4%.
Go North on US 99 to Bakersfield
Go South on US 99 to Los Angeles
Return to US 99 Introduction