ABSTRACT
Drivers are often poor at judging speed and distances. Laboratory studies (e.g. Groeger, Grande & Brown, 1991) and field trials (Cavallo & Laurent, 1989) indicate that drivers greatly misjudge the time it will take to reach a stationary object in their path or adjacent to their path (e.g. Groeger & Cavallo, 1991). The results of many studies indicate that when drivers would actually take some 2 to 3 seconds to reach the distant object their estimates are highly accurate, but beyond this distance they systematically underestimate the time it would take to reach the object. If these results were directly applied to the car following task, one might expect that alert drivers following other vehicles at short headways (i.e. temporal separations of less than 2 seconds) do so willingly. One would also expect that drivers choosing to leave longer following distances will actually follow substantially further behind than they would wish. Such longer headways do not directly reduce safety, although they may encourage other drivers to make unsafe use of these longer gaps in traffic, but they certainly reduce the numbers of vehicles which can use any particular stretch of roadway.
