This study was a field validation of the effectiveness of an auxiliary high-mounted stoplamp in reducing rear-end collisions. A previous study (DOT-HS-803-467), using taxi-cabs, found a 54 percent reduction in relevant rear-end impacts to vehicles equipped with the auxiliary stoplamp.
The present study used 5,400 telephone company passenger vehicles, half test, half control, which accumulated 55 million miles during a 12-month continuous data collection period. The results showed a statistically significant 53 percent reduction in relevant rear-end impact rate in the test group as compared to the control group. The findings were thus consistent with the previous study on taxicabs.