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Downhill Speed Information System
pic of speed advisory sign

Truckers get a white-knuckle experience traveling Interstate 84 from La Grande to Pendleton as they lose 2,000 feet of elevation and twist through a double hairpin turn at a 6% downgrade on Emigrant Hill, also known as Cabbage Hill. Now a new advisory system is cautioning transponder-equipped trucks about the steep downgrade so drivers will slow to a safe speed. The system is linked with the Green Light  preclearance system at the Emigrant Hill weigh station. If a truck is equipped with a Green Light transponder, a variable message sign displays a personalized message for the truck and a recommended speed that is based on that truck´s weight as recorded when it passed the Emigrant Hill weigh station. Watch an mpg movie of the sign in action.

Emigrant Hill, from mileposts 219 to 228, has historically experienced a plague of crashes. In the five-year period from 2003 through 2007, the area had 51 truck crashes involving a fatality, injury, or disabling damage to any vehicle, including 31 in which a truck was at-fault. The crashes resulted in 21 injuries and 2 deaths.

The new speed advisory system is designed to help inexperienced drivers who don´t realize how difficult it is to slow to a safe speed once they get started down this hill. When following trucks here it´s not uncommon to see smoke coming from the back of a truck as its brakes heat up. Emigrant Hill has a runaway ramp that trucks can use as a last resort to escape serious trouble.

Recommended speed
pic of recommended speed sign

At Emigrant Hill, an Interstate 84 roadside sign shows recommended speeds for trucks with five axles or more on such downgrades, ranging from 37 mph for trucks weighing between 60,000 and 65,000 lbs. to 18 mph for trucks weighing between 75,000 and 80,000 lbs.

The new advisory system displays one of these recommended speeds whenever it recognizes a transponder-equipped truck that was weighed in-motion upstream at the Emigrant Hill weigh station. However, a transponder-equipped truck that weighs less than 60,000 lbs. or more than 80,000 lbs. sees a personalized message with no indication of a recommended speed. The variable message sign just shows the company name and a STEEP DOWNGRADE warning. Eventually the system will be enhanced to show recommended speeds for other truck weights.

International Road Dynamics (IRD), Saskatoon, Canada, worked with the Oregon Department of Transportation to install the system in December 2002. It´s the world´s first advisory system capable of displaying a personalized message that includes both a trucking company name and a recommended safe speed for the truck. IRD has installed a similar system in Colorado on Interstate 70 at the summit of one of the Rocky Mountains. It also uses weigh-in-motion scales to determine the recommended speed for each truck, but it doesn´t have transponder-recognition capabilities.

A Downhill Speed Information System has long been a part of Green Light program plans. When Oregon administrators gathered in 1993 to write a strategic plan for using intelligent transportation systems for commercial vehicle operations, their vision included such safety enhancements: Site-specific highway warning systems could be installed at areas where weather-related hazards for trucks are common. Certain mountain passes will be equipped with devices that measure the speed of passing trucks and provide a variable message sign to indicate safe operating speed under existing weather conditions.

Road and weather information systems are now deployed throughout Oregon and travelers can get real-time information at ODOT´s TripCheck Web site.