hawkeye08
Elite Member
Just a quick internet search brings a wealth of information. From one article, you can see in the summary that the time varies greatly, depending on the situation. (http://www.harristechnical.com/articles/human.pdf)
5 seconds seems like a good compromise for this discussion.
SUMMARY
So what's a reconstructionist supposed to use? Sadly, there's no definitive answer except that 1.75 sec (daytime) and 2.5 sec (nighttime) are probably good places to start. Dr. Robert Dewar, who has conducted research on human factors in traffic safety since 1971, sums it up best this way. "The proper 'reconstruction' of a traffic accident must take into account the various potential human factors that could have contributed to the accident. After all, driver error (and pedestrian error) becomes a contributing factor in the vast majority of traffic accidents."
Some studies indicate that at night, because of restricted vision and driver expectation, that the time to perceive, react and maneuver is considerably longer. In a video presentation prepared by the 3M Company, "The Beauty of Conspicuity," a section on Decision Sight Distance explains that the Federal Highway Administration (FHWA) commissioned Biotechnology to study the time/distance situation regarding nighttime rear-end accidents.
The study results show that a driver "with average reflexes, eyesight, decisiveness and sobriety, driving an average car" [at 60 miles an hour] will take almost three seconds to see and recognize a hazard, almost seven seconds to decide on a course of action, and almost four-point-five seconds to complete a maneuver."
This is not to say, the study goes on, that the rule to allow 100 feet of stopping distance for each 10 mph, is entirely invalid. But at night, when a tractor-semitrailer is blocking the road, motorists must identify the problem when they are one-quarter mile away. Therefore, in the 14.5 seconds necessary to see, perceive (recognize), decide what to do, and then do it, a vehicle will travel 1,276 feet. If the recognition begins a quarter mile away (1,320 ft), the motorist has a "cushion" of 44 feet.
5 seconds seems like a good compromise for this discussion.
SUMMARY
So what's a reconstructionist supposed to use? Sadly, there's no definitive answer except that 1.75 sec (daytime) and 2.5 sec (nighttime) are probably good places to start. Dr. Robert Dewar, who has conducted research on human factors in traffic safety since 1971, sums it up best this way. "The proper 'reconstruction' of a traffic accident must take into account the various potential human factors that could have contributed to the accident. After all, driver error (and pedestrian error) becomes a contributing factor in the vast majority of traffic accidents."
Some studies indicate that at night, because of restricted vision and driver expectation, that the time to perceive, react and maneuver is considerably longer. In a video presentation prepared by the 3M Company, "The Beauty of Conspicuity," a section on Decision Sight Distance explains that the Federal Highway Administration (FHWA) commissioned Biotechnology to study the time/distance situation regarding nighttime rear-end accidents.
The study results show that a driver "with average reflexes, eyesight, decisiveness and sobriety, driving an average car" [at 60 miles an hour] will take almost three seconds to see and recognize a hazard, almost seven seconds to decide on a course of action, and almost four-point-five seconds to complete a maneuver."
This is not to say, the study goes on, that the rule to allow 100 feet of stopping distance for each 10 mph, is entirely invalid. But at night, when a tractor-semitrailer is blocking the road, motorists must identify the problem when they are one-quarter mile away. Therefore, in the 14.5 seconds necessary to see, perceive (recognize), decide what to do, and then do it, a vehicle will travel 1,276 feet. If the recognition begins a quarter mile away (1,320 ft), the motorist has a "cushion" of 44 feet.