Effect of Environmental Optical Flow Rates on Driving Speed Control

A driving simulation experiment was performed to investigate the effect of environmental optical flow rates manipulated by drivers eye-levels(EL) on their driving speed control and information processing. In this experiment, subjects at four ELs(2, 4, 6, and 8 feet) were asked to drive without the aid of a speedometer under varying road conditions and driving target speeds. The results showed (1) significant effects of EL and road complexity on drivers driving speed control: drivers at higher ELs and simple road condition generally drove faster than those were at lower ELs and complex road condition. But this tendency was restricted to only the EL-4 and EL-6 comparison: more extreme ELs did not increase the effects. Also (2) effect of EL and road complexity interacted with target speed condition. For example, higher EL did not induce faster driving speed at the lowest target speed condition, but difference in driving speed due to road condition was found only at the lowest target speed condition. (3) The drivers in the lower ELs(2 or 4 feet) undershot at the higher target speeds, whereas, the drivers in the higher ELs(6 or 8 feet) overshot at the lower target speeds. Therefore, (4) the description of the functional relationship between the EL and driving speed requires considering different road types and target speeds together, as no single function characterized all conditions.