The momentum point is very valid. But the slower speeds provide more time for drivers and others to react. That in turn gives you much more time to break and scrub off that extra momentum.
At 50kph your reaction distance is about 15 meters, at 25kph it’s half that at 7.5meters. (Assuming reaction time of 1 second, which seems to be a realist value).
7.5 meters is quite a bit of distance, and in a busy city will make a lot of difference.
that is a bold statement to make from the video information we got, at least in my opinion. I would estimate the speed to be at least 50 km/h which gives 25 m as a very rough estimate for the stopping distance without reaction time. It's probably better than that but not 8 m.
But I do agree that the car doesn't seem to have stopped at all and missed the victim completely.
Speed determines time to stop including stopping distance and reaction time. For every second of reaction time per 10kmph you add about 4 meters of distance travelled before you even hit the brakes. So best case if you aren't looking at your HVAC, at 50kmph you will start the stopping process in about 28 meters, and at 60kmph it will be 33.3m and take longer to stop once you hit the pegs.
Doesn't sound like heaps but that is actually your margin for error, just 4m. If something jumps out in front of you at 28 meters away, at 50 you will have had 4 meters to stop, which modern cars can do, and at 60 you will hit them at the full 60kmph. The Australian government has some great road safety clips on the subject, I might try and find them.
That calculation would probably be wrong anyway, unless you have a lot of practical experience with emergency braking. I constantly underestimate my reaction times.
At 38 MPH, the car would cover that distance in 0.7 seconds. That is on the low end of human reaction times for braking, so an average person might not have time.
50 ft is 15 meters and change, at regular car speeds that is much shorter than your reaction speed. It's essentially an accident waiting to happen. At highway speeds you should be looking about 200 ft ahead of you for safe driving. See the 'two second rule', and that's for clear skies, daylight:
!!!! 2 meters separation at 70 km/h gives you a tenth of a second to react to anything the car in front of you does, that's flatly insane. Where in the world do people drive like that?
Seriously, that's objectively insane. Try the ruler drop test for reaction times if you don't believe me, a 10th of a second to even initiate your response isn't realistic and obviously gives no time for the response itself to have effect. What I'm saying is that at a tenth of a second, you can't even start to press the brake pedal in time, let alone have enough time to actually slow down.
In America, with only 2 meters between vehicles the traffic would be inching forward at a snails pace, under 20 km/h at least. "Stop and go", as in people would stop their car and then drive forward slowly when a larger gap ahead of them appears.
> In other words, these drivers did not leave enough distance to react and brake.
Again, recommended following distance is ~250-300 feet when stopping & reaction time can be 350-400 feet. This is OK when the car in front of you brakes, because you'll both be decelerating with a similar profile and you'll have more than 250-300 feet to stop. It is not OK when the car in front of you stops substantially faster than braking with no warning because it has hit an unknown obstacle.
No it's not, and hitting the brakes isn't "full control". Honestly, how long do you think it would take you to hit the breaks if something jumped out at you? It would be almost instant.
Edit: ok, I was just making a bit of a joke at first, but I looked it up. Reaction times vary by person, but tend to be between 0.75 and 3 seconds. 2.5s is used as a standard, so I guess I have to conceded that 1.25s is pretty good... I guess, for whatever that's worth.
Probably want to get those brakes checked. Stopping distance from 65 MPH should be no more than about 150 feet. Reaction time at 100 feet/second will probably be another 100-150 feet.
With instantaneous reaction time, the actual braking distance is around 10m unless you jump in front of an escalade or a land rover...
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