two thirds of a second. (according to the diagram of shortest stopping distances in my Highway Code ISBN 0115509623)

If using a cell phone.... about twenty minutes.

I've heard 3/4 second in the traffic schools that I've attended, so I'm sure that's the figure according to the California Vehicle code. I figure it's probably about 3/8 second, if you're paying attention and driving on cruise control.

About one second.

Ther last person who answerd this question must have been sleeping when he timed himself. I tried this at a police road show a few years ago and the average time was 0.4 seconds, this test was done by watching a video and reacting to what happens on the screen.

Highway code tests were done where a driver was asked to watch a light bulb, and react by pressing the brake pedal when the light was illuminated. The results claim a reaction time of 0.68 seconds. This is clearly an unrealistic reaction time as the test subjects were expecting the stimli required. More recently, tests done using a video simulated driving scenario allowed the test subjects to drive for a considerable time before a hazard was presented to them and real reaction times were established ranging from 1.4 to 1.9 seconds dependant on age/experience.

1) "While every person is different, the average “perception and reaction time” is around 1.5 seconds for a sober driver in daylight conditions. The amount of time needed can increase during poor weather conditions, at night, or when a driver is impaired by drugs or alcohol. The more time it takes to react, the longer the total stopping distance will be. On an average day, 1.5 seconds will have gone by before you’ve even touched the brake pedal." Source and further information: http://www.firerescue1.com/Columnists/Chris-Daly/articles/239741-Stopping-Distances-Part-1/ 2) "The defense in the Jones family's case argued that Susan would have had plenty of time to avoid the collision because the "standard" perception-reaction time is 1.5 seconds. (19) Most people do begin to respond to simple stimuli within 1.5 seconds, with the fastest response time probably being around .75 seconds. But the studies that support this general rule were based on tests of straightforward situations that required predetermined, simple responses. Also, the tests did not measure the time it took the subject to execute the action. We argued that such studies are not appropriate for calculating perception-reaction time under the conditions that existed during Susan's accident. The defense also attempted to compare Susan's perception-reaction time to an "average" or "norm" reported in older studies. We countered this by showing that recent, more accurate studies reported their results as percentiles, not as averages or medians. Because the median or average does not take into consideration the scatter of the data, using percentiles produces a more accurate figure when determining the meaning of a particular result. For example, if Susan's results were at the 85th percentile, it would mean that 85 percent of the test subjects responded in that amount of time or less. That is certainly a better indicator of what is "normal" or "prudent" than the average of the results. (Note that the question is not how Susan performed as compared to an "average," but whether her performance fell within a range associated with representative individuals performing the same sort of task.)" Source and further information: http://goliath.ecnext.com/coms2/gi_0199-6285488/In-the-eyes-of-the.html Further information: http://www.harristechnical.com/articles/human.pdf

i was at the Ontario Science center toronto. they had an ininteractive.. ummmm... thingy... and you sit in a fake car and test your responce time. i say its normally .5 seconds... but after practice people could get down too about .2-.3 seconds.