Headway comfortable

Lewis-Evans, B., de Waard, D., and Brookhuis, K.A. 2010. That s close enough—a threshold effect of time headway on the experience of risk, task difficulty, effort, and comfort. Accident Analysis and Prevention, 42, 1926-1933. 

Taieb-Maimon, M. and D. Shinar (2001). Minimum and comfortable driving headways reality versus perception. Hum. Fact, 43(1), 159-172. 

When we drive behind another vehicle in traffic, we do not maintain a fixed distance or time to the car ahead. Instead, we oscillate between some minimal safe headway that we try not to go under, and a headway that we consider neither too far not too close. These two extremes define our range of comfortable headways (Ohta, 1994). To avoid colliding with a vehicle ahead of us, we therefore have to maintain a time headway that is longer than our brake reaction time in that situation. Based on studies of brake reaction times, a commonly recommended headway is 2 seconds, and a method that is commonly recommended to drivers in order to apply that rule is to wait until the lead vehicle crosses a definable point (such as a roadside post) and then count two seconds (e.g. twenty one, twenty two ) if we pass the definable point before we finish our coimting than our gap is too short. This is known as the 2-seconds rule. In contrast to... 

In a series of studies that we conducted in Israel we looked at drivers choices of safe and comfortable headways, tiieir ability to verbally and non-verbally estimate headways, the relationship between the headways drivers keep and their skills, their ability to improve their judgments, and the potential for feedback devices as learning tools to increase headways. The following is a brief description of these studies and their results. 

Drivers estimation of minimum safe headways and comfortable headways... 

In the first study (Taieb-Maimon and Shinar, 2001), experienced drivers with Snellen visual acuity of 6/9 or better were asked to drive on a four lane divided highway behind a lead vehicle. An experimenter that drove the lead vehicle adjusted its speed in a random fashion from 50 to 100 km/hr. At each speed, the driver in the following car was asked to follow the lead car by keeping a minimal safe distance at vdiich he or she would still be able to stop in time should the driver of the lead car bre suddenly . Once the drivers reached that headway they were asked to estimate that gap - either in terms of meters, car-lengths, or seconds. Then the drivers were asked to slow down so that the gap widened significantly. They were then asked to follow the lead vehicle at what they considered a comfortable distance. Once this procedure was completed the lead driver selected another speed and the whole sequence was repeated. 

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