A total of 16 drivers (8 ages 16-30, 8 ages 65 or older) drove a driving simulator at approximately 45 mi/hr while following either a car, pickup truck, school bus, or tractor trailer. They drove on a winding two-lane road as they normally would, but were instructed not to pass the lead vehicle. The variance of the lead vehicles was either low (4.2 mi/hr) or high (for the car and pickup truck only, 7.1 mi/hr). They also identified signs when they appeared. In general, older drivers followed at a greater distance than younger drivers (469 vs. 282 ft) and some older drivers followed so the lead vehicle would be out of sight (600 ft). These following distances, corresponding to headway times of 4.3 and 7.1 s, are much greater than are typically reported from on-the-road studies. Although subjects followed cars about 10 percent closer than other vehicles, there were no other effects of vehicle type or its speed variability (within the range explored) on following distance. Further, both mean lateral position and the standard deviation of lateral position were unaffected by lead vehicle type or their speed variance, though there were significant individual differences. The lack of influence of vehicle characteristics may result from the absence of following traffic (and a rear view mirror to see such) in this simulation, so the pressure to keep up with traffic was missing. This suggests that following studies may require simulations to include a rear visual channel. (Author/publisher)
Abstract