Quote:
Originally Posted by keyur What's with you and the speed limits and ABS?
ABS kicks in when :
1. There is relative speed difference after braking
2. There is sudden deceleration due to braking (not gradual).
This has nothing to do with speed! |
Let me clarify again.
Speed has to do with the driver's ability to react, and therefore whether or not ABS activates. In this case it is because someone was at a speed above both the recommended envelope and their personal abilities and experience, and then could not react appropriately when confronted with an unfamiliar situation. Even in the cases you have mentioned, if the surface and tyre are very grippy (hot road and tyres) the extent of ABS activating will be very low. It only prevents wheels from locking, so that you have traction at all times when braking. It does not retard or enhance actual braking performance (theoretically a little shorter stopping distance, but that varies by implementation).
As for the speed limit, it is mentioned keeping in mind at what distances obstacles become apparent, the nature of the road and all its users, and the average stopping time of every different kind of vehicle on the road.
Once you are outside those limits you are on your own and cannot blame the machinery for failures. It's like overclocking a computer. You can do it and do it safely and push everything beyond recommended spec (and even compete for the highest levels of push), but you cannot blame the hardware for failures, loss of money or warranty.
To get back to this situation - had the speed been lower, panic braking may not have been necessary -> no ABS would have kicked in -> the pedal action would have been normal -> the driver would not have panicked -> accident would not have happened.
Let's assume the car was travelling at 140 km/h at the point in time the brakes were applied, this is about 38 meters per second. At 80 km/h the speed is about 22 meters per second. In the 7-8 seconds of a braking action required the car would have travelled an additional 50 meters if it was at the higher speed, which means the obstacle had to be seen 50 meters before it actually appeared.
Also keep in mind I have not accounted for the much higher (2x) braking forces required to slow down something with much more momentum. In reality from 60mph the total braking distance (to zero) is close to 130 meters (panic braking including a one second delay between recognising the obstacle and applying the brake) for an average European sedan. From 50mph the distance is close to 80-90 meters. At 100mph the distance is close to 250 meters. These are very long distances, you have to see a 100 meter track to understand what we are talking about.
I really respect your fortitude in stopping to help. Much admired and one of the things I wished I had done. However not sure that the accident was due to ABS, but an irresponsible and inexperienced driver. That's all.
Frankly, the first time I felt ABS working it scared the hell out of me, but in that case I kept my foot buried as hard as I could as I didn't have an option. I was at about 90 and a trailer decided my lane was more appetising than the one they were on. I had no choice but to keep it buried because I would have gone under the trailer, the car stayed on line, obeyed the steering, and slowed down sufficiently to avoid any mishap. Since then, I know exactly what to expect and thank the manufacturer for putting it in there.