Cajon Pass is a mountain pass in southern California dividing the San Gabriel and San Bernardino mountains. Cajon Summit is located on Interstate 15 approximately 11 miles south of Victorville, CA. Interstate 15 connects to both I-70 and I-40 and links the Los Angeles area ports to the Midwest and eastern US.

Southbound I-15, from the Cajon Summit, has a steep vertical descent of about 1160 feet over the first 5 miles with a continued lesser descent for about 12 more miles. The reported grade for the southbound descent is 6% over 4 miles. A truck scale is located about five miles south of the summit. Interstate 15, between Cajon Summit and the truck scales, has a very steep 6% grade segment. Since trucks will likely have to stop at the truck scale on this grade, using a low gear it is extremely important to conserve their brakes.

Northbound I-15 from Cajon Summit to Victorville has a vertical descent of only 1,144 feet over 11 miles. This descent is a very mild and steady, a 1 to 2% grade.

Cajon Pass is well known for being the inspiration behind Clessie Cummins' "Jake Brake". In 1931, most heavy trucks were powered by gasoline engines. Cummins was promoting the diesel engine both as a better alternative and to raise publicity for the diesel engine. He and a crew of two other men attempted to set a new cross country truck speed record. The route for this trip took them across Cajon Pass that at the time was traversed by U.S. Route 66. As legend has it, the truck reached Cajon Pass after sunset on the fifth day.
Cummins knew there was a grade ahead but did not recognize the Spanish word Cajon on the sign marking the pass to be the "Kayhone" pass he was looking for. As a result the truck started down the grade in too high of a gear causing Cummins and crew to be subjected to a white knuckle ride to the base where they narrowly escaped a collision with a train's caboose at a rail crossing. After this trip, it is said that Cummins was determined to make his diesel powered trucks perform as good as gasoline powered trucks on downgrades. Years later, Cummins created the Jacobs Engine Brake that allows diesel engines to perform much better on downgrades.

Pass Name: Cajon Pass
Traversed by Highway: I-15
Summit Elevation: 4260 ft
Summit Conditions: Large brake check area for southbound trucks

Base Elevation: 3100 ft
Vertical Distance: 1160 ft
Driving Distance: 5 miles
Posted Speed Limit: 70 mph/ 45 mph for trucks
Steepest Reported Grade: 6 % for 4 miles
Calculated Average Grade: 4.3%
Number of Lanes: Four southbound
Runaway Ramps: One on right 2.9 miles from summit
Brake Check Stations: One at summit
Required Stops: One at a weigh station, 5.2 miles from summit

Mile Marker Elevation Change in Elevation Percent Grade
0 4260 ft.
1 4149 ft. 111 ft. 2.1%
2 3851 ft. 298 ft. 5.6%
3 3563 ft. 288 ft. 5.4%
4 3349 ft. 214 ft. 4.0%
5 3100 ft. 249 ft. 4.7%
6 3000 ft. 100 ft. 1.8%
7 2942 ft. 58 ft. 1.0%
8 2863 ft. 79 ft. 1.4%
9 2883 ft. -20 ft.
10 2680 ft. 203 ft. 3.8%
11 2463 ft. 217 ft. 4.1%
12 2246 ft. 217 ft. 4.1%
13 2073 ft. 173 ft. 3.2%
14 1940 ft. 133 ft. 2.5%
15 1839 ft. 101 ft. 1.9%
16 1745 ft. 94 ft. 1.7%

Cajon Pass Southbound

Crash : John C. Glennon, Chartered Contact Us Links Home