Knowledge Resources

The U.S. DOT sponsored an independent evaluation of a field operational test (FOT) of three advanced intelligent vehicle safety systems (IVSS): collision warning systems (CWS), adaptive cruise control (ACC), and advanced braking systems (AdvBS).

• CWS installed on fleet vehicles (tractors) used in-cab visual displays and audible alarms to notify drivers to take corrective action if forward radar sensors detected a potential crash.
• ACC maintained set headways between tractors and lead vehicles, and was designed to operate as a conventional cruise control system if no lead vehicle was present.
• AdvBS installed on fleet vehicles used air disc brakes and an electronically controlled braking system to enhance braking performance and reduce stopping distances.

Data acquisition systems (DAS) were used to assess safety impacts "with" and "without" IVSS technologies installed on 100 trucks for 30 months starting in 2001. The following three combinations of IVSS technology were evaluated.

• CWS
• ACC + AdvBS
• CWS + ACC + AdvBS (bundled system)

Impacts on crash rates were estimated based on an analysis of the frequency and severity of rear-end driving conflicts encountered. A driving conflict was defined as a safety-critical situation that had potential to result in a crash if the driver did not react quickly or sufficiently.

FINDINGS

The results indicated that trucks equipped with CWS or the bundled system (CWS + ACC + AdvBS) can avoid up to 21 percent or 28 percent of rear-end crashes, respectively.

CWS was the most effective IVSS technology. The safety benefits, however, were dependent on the percentage of time the trucks were traveling at highway speeds (speeds greater than 55 mi/hr). The analysis indicated that CWS equipped trucks that travel at highway speeds more than 75 percent of the time have a statistically significant reduction in exposure to conflicts. However, CWS equipped trucks that spend less than 35 percent of their time at highway speeds are exposed to more conflicts than trucks without CWS.

Historical data show that 40 percent of all tractor-trailer rear-end crashes and 36 percent of large truck rear-end crashes are preceded by a conflict that involves a truck driving at a constant speed that encounters another vehicle driving more slowly in the same lane (General Estimates System (GES) and Fatality Analysis Reporting System (FARS): 1999 through 2003). The results of the FOT indicate that trucks equipped with CWS can eliminate up to 52 percent of these types of conflicts and the bundled system can eliminate up to 61 percent.