If drivers can easily get the information they need and know what to expect, they can manage themselves in traffic more effectively. And traffic engineers try to oblige. As head of the human factors program for the U.S. Federal Highway Administration, Alexander developed the concepts of Driver Expectancy and Positive Guidance that play an important role in the design of today's highways. But while engineers have made great gains in providing guidance cues for drivers there are still many problems. The down side of making roads and traffic more predictable is the complacency this can engender in drivers.
Drivers gather much of their information subconsciously.
In a non-threatening environment inattention becomes the threat, and it can lead to disaster, particularly when a driver is impaired. The impairment doesn't have to be alcohol or drugs. Fatigue, distractions, or anything else that affects the ability to efficiently divide attention, select information, and make decisions, can cause problems. In the Curnoe case, some of the cyclists recall a striking visual effect in a nearby field as a barn appeared to be floating in flood waters from the Thames river. This could be a powerful draw on the attention of a driver who has missed seeing hazards on the roadway.