To simulate some of the toughest conditions a truck and trailer combination will face, the J2807 “Highway Gradeability” tests take place on a well-known stretch of Arizona highway, the 11.4-mile-long Davis Dam Grade. If trucks are not tested on this specific stretch of steep road, they can be run in a simulation using a “climactic” wind tunnel. Ambient temperature plays a significant role in this test with a minimum temperature of 100 degrees required at the base of the grade. In addition to a hot climate outside the truck, the test requires the air conditioning system to be set at maximum cold, with outside air selected (not recirculating) and the fan running at full blower speed.
Once those criteria are met, the evaluation can begin on the famous stretch of SR 68 between Bullhead City and Golden Valley, Arizona. To pass this test, a truck-and-trailer combination must be able to drive at 40 mph (35 mph for dualies) and never drop below that speed until the end of the test segment at the peak of Union Pass. Testdrivers are allowed to go faster than the minimum speed requirement in the sections of the grade where posted speed limits are 55 mph and 65 mph, but there are other requirements the vehicle must still meet. Under “drivetrain system performance,” the J2807 standard requires there be no component failures, along with no “check engine” lights or any other alerts or warnings for the driver. The “cooling system performance” requirement also requires zero part failures, no error codes, no driver warnings of any other kind, and no loss of coolant fluid during the test.