Driver Behavior as a Function of Ambient Light and Road Geometry

OBJECTIVES To determine how ambient light (day versus night) and road geometry affect driving behavior,especially the speeds that drivers choose when not constrained by lead vehicles.METHODSRecently, it has become technically easier to observe how people drive b offering them longtermuse of highly instrumented vehicles. Much of this type of work has been done in connectionwith large-scale field operational tests (FOTs) of various innovative vehicle systems. Theinformation obtained is in many ways complementary to information from observation of traffic.Traffic observation often provides information about a large number of drivers, but at a relativelycoarse level and in a spatially and temporally limited context (i.e., observing how a large numberof drivers negotiate a particular intersection). In contrast, long-term use of highly instrumentedvehicles is more restricted in terms of how many drivers can be observed, although the feasiblenumbers are now reasonably high. On the positive side, data from instrumented vehicles canoffer very detailed information about driving behavior over many miles and many days.In this paper, we present results from a database of driving behavior that was derived from arecent FOT for an adaptive cruise control (ACC) system (although the data used here are all fromphases of the study that involved only normal vehicle equipment). The FOT involved tenidentical cars that were instrumented for a variety of types of data. The most important data forpresent purposes were: speed, yaw rate, location from the Global Positioning System (GPS), andpresence or absence of a lead vehicle within about 100 m based on the forward-looking sensorsof the ACC system. The instrumented cars were driven by a total of 108 participants, each ofwhom was given a car to use as his or her own vehicle in normal driving for either two or fiveweeks. The participants were sampled from licensed drivers in southeastern Michigan, andrepresented a wide range of age and driving experience.RESULTSResults will be reported in terms of speed as a function of horizontal road curvature in light anddark conditions, and as a function of driver age and gender, all for situations in which there is nolead vehicle within about 100 m. CONCLUSIONSCurrent evidence about headlighting suggests that drivers’ ability to see and negotiate theroadway is virtually unaffected by differences in ambient light, although their ability to perceiveand avoid objects on the road, such as pedestrians, is greatly reduced when headlamps are themain source of light. There is also evidence that drivers do not markedly reduce their speed inconditions of low ambient light. The current analysis allows us to determine how drivers react tospecific road geometries in light and dark conditions. This has implications for how well drivers’perceptual abilities match their driving behavior, and also for assessing the potential benefit of avariety of innovative headlighting systems that are currently being designed to adapt in variousways to vehicle speed and road geometry