Auto safety and human adaptation

Issues in Science and Technology, Winter 2000/2001 by Smiley, Alison

Although the amount of time that drivers spend looking at navigation displays raises safety concerns, there is also reason to believe that drivers adapt appropriately to increases in traffic. The time drivers spend glancing at signs in high-density traffic is about half that found in low-density traffic. Similarly, drivers using a map-based navigation system in an on-road study had glance durations 30 percent less than those in a simulator study where the traffic demands were lower.

An on-road study using a map display navigator examined the influence of traffic density on attention to the display. Subjects used the system to drive in unfamiliar areas that varied greatly with respect to traffic density. The driving difficulty of various road sections was rated and compared to driver eye scan patterns. As driving difficulty increased, the probability of a glance to the roadway center increased, whereas the probability of a glance to the navigational display decreased. In addition, the length of glances to the roadway center increased for high-density as compared to low-density traffic and even more so when critical incidents occurred.

These data suggest that most drivers will tailor their glances at in-vehicle displays or tasks to the driving workload. However, it is necessary to examine changes in the detection of on-road hazards to be sure that safety is not compromised. Such an approach was taken in a study using the Federal Highway Administration driving simulator to compare driver detection ability, as well as car control, for various types of navigation systems, including maps, auditory messages, and visual displays. The detection task involved watching dashboard instrument gauges for out-of-range indications. Various driving scenarios were used to vary the difficulty of driving and the difficulty of the detection task. Drivers appeared to cope with greater display complexity and greater task difficulty by dropping their speed and by reducing the attention paid to the detection task. The detection task was performed most poorly for the paper map group and next most poorly for the complex map display. Overall, subjects missed 16 percent of the signals presented. Older subjects using the complex map display or the paper map missed large numbers of signals (approximately 40 and 50 percent, respectively). Other types of visual and auditory devices (with the exception of the paper map) were associated with much lower miss rates.

Although this study did examine changes in attention, the task used was one of watching gauges inside the car. The more critical task in driving is watching the road for hazards such as pedestrians, bicyclists, or debris. The effect of navigation systems on such detection remains to be studied.

There has been little research addressing how any high-tech device changes the extent of driving. One Japanese experiment demonstrates some interesting adaptive effects of a navigation system. The results showed that lost drivers benefited from car navigation information and revised their route more easily than those who used maps. Users of car navigation systems appeared to worry less about the consequences of becoming lost and therefore intentionally traveled more on neighborhood streets to avoid congested arterial streets. Widespread use of such systems and traffic congestion information may increase neighborhood congestion unless countermeasures are taken.