Brake reaction time

The distance in which the vehicle comes to rest after the driver discovers a hazard that requires stopping. Includes driver reaction time, brake reaction time, and braking time. Toxemia... 

The prebraking distance includes perception time plus reaction time. Perception time is the time for recognizing that one should start braking. Reaction time is the time necessary to move the foot onto the brake pedal and begin braking. 

Johansson G. and K. Rumar (1971). Drivers brake reaction times. Hum. Fact., 13(1), 23-27. Kahane C. J. and E. Hertz (1998). The long-term effectiveness of the Center High Mounted Stop Lamp in passenger cars and light trucks. NHTSA Technical Report No. DOT HS 808 696. U.S. Department of Transportation, Washington DC. 

McKnight, A. J. and D. Shinar (1992). Brake reaction time to center high-mounted stop lamps on vans and trucks. Hum. Fact.., 34(2), 205-213. 

Perception Reaction Time And Brake Reaction Time... 

It should be clear by now that it takes time to see and respond . The expression to stop on a dime is just that an expression. The time it takes from the moment a sound wave reaches our eardrum, or a light ray impinges on our retina, until we initiate a response to that stimulus is known as perception reaction time. In driving, the time that passes from the moment a stimulus - such as a brake light or a stop light - appears until we actually reach the brake pedal is known as brake reaction time (BRT). 

Table 5-4. Total stopping distances from different speeds assuming a braking reaction time of 2.5 seconds, (from Leibowitz et al., 1998, with permission from Elsevier).

As we move away from the sterile laboratory environment to a more complex one such as a driving simulator, or an experimental study on the road, or a naturalistic road study we can expect perception reaction times and brake reaction times to increase. And they do. In a review of 31 studies of brake reaction time. Green (2000) noted that mean times varied from a short 0.42 seconds (when drivers in a simulator responded to an expected light while impaired by carbon monoxide Wright and Shephard, 1978) to a high of 1.95 seconds (for older drivers responding to an unexpected stop by a policeman Summala and Koivisto, 1990). 

Figure 5-2. Perception reaction times (PRTs) and foot movement times (MTs) to a brake light, in a laboratory situation. PRTs are from the onset of the brake light to the initial release of the accelerator pedal. MTs are from the accelerator pedal to the brake pedal. Total braking reaction time is the sum of PRT and MT (from Warshawsky-Livne and Shinar, 2002, with permission from Elsevier).

Table 5-5. Drivers average brake reaction times in a car-following situation in response to different stimuli as a function of signal quality, driver status (standing or moving) and expectancy. Note that the reaction times increase as the driving situation becomes more complex and the event uncertainty increases (from Matson, Smith and Hurd, 1955, as cited by Shinar, 1978, with permission from McGraw Hill).

In an attempt to consider that variability, and to identify different components of brake reaction time that can be affected by it, McGee et al. (1983) reviewed the literature on individual differences in reaction times. Their summary of reaction times is reproduced in Table 5-6. In... 

Table 5-5. Brake reaction times to unexpected roadway hazards based on the component times for different proportions of the populations, from the 50 to the 99 percentiles. Based on data from different sources (from McGee et a ., 1983).

We can get an appreciation for the variability in actual brake reaction times from the results of a field study by Johansson and Rumar (1971). In their study, drivers were stopped and notified that somewhere down the road within the next 10 km they will hear a klaxon (an electrically... 

Figure 5-3. Distribution of driver brake reaction times to a loud horn. The narrow distribution on the left is of the experimenter s reaction times. The drivers reaction times are the true break reaction times, after subtraction of the experimenter s mean reaction time (from Johansson and Rumar, 1971, with permission from the Human Factors and Ergonomics Society).

Figure 5-4. Cumulative brake reaction time distributions of young drivers to a high-contrast obstacle on the road under three levels of expectancy x = unalerted , o = surprise , and A = brake . See text for explanation (from Olson and Sivak, 1986, reprinted with permission from the Human Factors and Ergonomics Society).

As can be seen from the cumulative distributions of reaction times, the brake reaction time is plotted on the X axis, and the percent of trials in which the drivers responded within each BRT is plotted on die Y axis. It is quite obvious that the lower the expectancy, the slower the reaction time. Thus, if we look at the 50 percentile of responses, we see that in the surprise condition the BRT was 1.1 seconds, in the alerted condition it was 0.7 seconds, and in the... 

Table 5-7, Brake reaction times of unsuspecting drivers to the change of a traffic signal light from green to yellow in the approach to different intersections in the same general geographic area (from Wortman and Matthias, 1983).

Table 5-8. Brake reaction time of unsuspecting drivers to various traffic control devices and roadway situations in Australia 85 Percentile in seconds (fi om Triggs and Harris, 1982).

Still, given the critical role that reaction time plays in emergency crash-avoidance situations, we must make some design decision concerning brake reaction times. This has in fact been done and various reaction times are commonly assumed for various design consideration, such... 

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... 

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