US 99 – Five Mile Grade

Historical Tour of old US 99

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Five Mile Grade : Castaic

Five Mile Grade from Castaic. Concrete in foreground marks one of the Palomas Creek bridges from 1951.
Five Mile Grade from Castaic. Concrete in foreground marks one of the Palomas Creek bridges from 1951.
Truck Escape Ramp in 1968 before the new southbound lanes were opened. Note the downhill traffic still using the roadway. Photo Courtesy - Gordon Glattenberg
Truck Escape Ramp in 1968 before the new southbound lanes were opened. Note the downhill traffic still using the roadway. Photo Courtesy – Gordon Glattenberg
Truck Escape Ramp in use.
Truck Escape Ramp in use.
Map of the Truck Escape Ramp.
Map of the Truck Escape Ramp.

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%.

This map shows all of Five Mile Grade from Castaic to Violin Summit. Note the two crossovers on each end of the grade.
This map shows all of Five Mile Grade from Castaic to Violin Summit. Note the two crossovers on each end of the grade.
This photo shows the highway in 1948 near the top of the grade just after it was widened.
This photo shows the highway in 1948 near the top of the grade just after it was widened.
About 2/3 up the grade, the highway split for a short distance as this map shows. The roadway to the right is the 1933 alignment and to the left is the 1948 widening. When Five Mile Grade was redone as a freeway, the split was removed and the new roadway took the 1948 side. The 1933 side was then buried and torn up.
About 2/3 up the grade, the highway split for a short distance as this map shows. The roadway to the right is the 1933 alignment and to the left is the 1948 widening. When Five Mile Grade was redone as a freeway, the split was removed and the new roadway took the 1948 side. The 1933 side was then buried and torn up.
Photo of the split near Violin Saddle from the 1950's.
Photo of the split near Violin Saddle from the 1950’s.
Five Mile Grade from Violin Summit in 1958. Courtesy - Caltrans.
Five Mile Grade from Violin Summit in 1958. Courtesy – Caltrans.

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