A dynamic truck down hill speed warning system installed on I-70 in Colorado reduced the average speed of passing trucks by approximately 5.2 mi/hr.
Date Posted
09/19/2001
Identifier
2007-B00478
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Evaluation of Downhill Truck Speed Warning System on I-70 West of Eisenhower Tunnel

Summary Information

In May 1998, a downhill speed warning system was deployed on a mountainous highway outside of Denver. The system was designed to influence driver behavior and reduce vehicle speeds as trucks emerged from the I-70 Eisenhower Tunnel and approached a 10-mile section of downhill grade (5 to 7 percent).

The system used weigh-in-motion sensors, inductive loop detectors, and computer hardware and software to monitor vehicle speed, weight, and axle configuration for trucks. A computer algorithm was used to compute a safe descent speed for each type of vehicle weighing more than 40,000 pounds, and a recommended speed/warning message was posted on a dynamic message sign (DMS) at the end of the tunnel.

To evaluate system impacts, truck weight, speed, and axle configuration data were collected upstream and downstream of the posted downhill warning message. At the Dumont weigh station located upstream of the tunnel, video camera and weigh station data were collected to supplement the weight and speed data collected by the WIM system inside the tunnel and at a video camera located at the tunnel exit. Two miles downstream, another video camera system was installed.

Truck activity was monitored with the system "on" and the system "off." The system was "on" from 11 AM to 1 PM on May 19 and May 21, 1999, and the system "off" from 11AM to 1PM on June 2 and June 4, 1999. Weather conditions were similar on each day and speed data upstream and downstream of the dynamic message sign was able to be calculated for approximately 30-40 trucks during each 2-hour sampling period. A two-tailed t-test was used to compare average truck speeds with and without the system active and an analysis of covariance model was used to account for an increased number of lighter (i.e. faster) trucks observed when the system was "off."
FINDINGS

The results of the study indicated the system was effective at warning truck drivers of dangerous behavior. The analysis showed that the average speed of passing trucks decreased by about 5.2 miles per hour with the system active.
Goal Areas
Deployment Locations