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Or, more interesting, a correlation between innumeracy and traffic deaths. It turns out that the distance required to bring a car to a stop (after reaction time

by lutusp 13y ago

Or, more interesting, a correlation between innumeracy and traffic deaths. It turns out that the distance required to bring a car to a stop (after reaction time) is proportional to the square of the vehicle's speed. This is something that most people don't know, and that young drivers ignore at their peril. After the driver reacts and presses on the brake pedal, on dry, level pavement, a car requires about 20 feet to stop at 20 miles per hour, 80 feet at 40 miles per hour and 180 feet at 60 miles per hour (all approximate distances). Simple equation (reaction time not included): y = v^2 / 20 v = velocity MPH y = stopping distance in feet Another reason to learn some mathematics and science (it's based on the kinetic energy of the moving car). :)

joosters 13y ago
Is that relevant? Most fatalities are not because the car drove straight into a stationary object directly in front of them on the road. So, total stopping distance doesn't come into play as you describe it. Collisions mostly happen because of the actions of car drivers who are going roughly the same speed as you. Not saying that speed is a factor, just that stopping distance isn't the thing. Perhaps you should discuss kinetic energy instead?
- jakobe 13y ago
  Stopping distance is extremely important. Here are a few examples of typical car accidents: - a driver in foggy weather crashes into a traffic jam - a car crosses an intersection at a red light, is hit by a car from the other direction - car hits a child running on the street - driver looses control, hits a tree at 60mph - reckless driver tries to overtake, hits car coming their way These types of accidents are the most lethal, and they are all due to stopping distance (and could be avoided by driving at a lower speed)
  - lutusp 13y ago
    > - a driver in foggy weather crashes into a traffic jam This is a particularly dangerous and often misunderstood case, because staying several car lengths away from the car ahead won't do any good if that car suddenly collides with a stationary car in front of it that's hidden by the fog. When the car you're following comes to a sudden stop, all the rules about safe following distance go right out the window. This is why professionals sometimes recommend just getting off the road when fog prevents a reasonable amount of visibility. > These types of accidents are the most lethal, and they are all due to stopping distance (and could be avoided by driving at a lower speed) Very true.
- lutusp 13y ago
  > Is that relevant? Only when a misjudgment of stopping distance is a factor, in one way or another. I'll bet that the car driven by actor Paul Walker's friend -- the car that crashed and killed both of them -- was an example where the friend thought he had enough distance for a safe stop. But at the estimated speed -- "more than 100 MPH" -- more than 500 feet would have been required and just wasn't there, before a sharp turn they didn't manage. > Most fatalities are not because the car drove straight into a stationary object directly in front of them on the road. Yes, but all such accidents involve cars hitting each other or objects along the road, or rolling over during efforts to stop them, and similar causes. All these examples involve energy management, and in each case, the driver couldn't safely dissipate the car's kinetic energy. > Collisions mostly happen because of the actions of car drivers who are going roughly the same speed as you. Not in any number of cases, like crossing over the center divider, or hitting a roadside object, or losing control in bad weather, or fog collisions, etc. etc.. And even if two cars have a relatively low-speed collision while both traveling at high speed, then the problem becomes controlling the cars after the collision and avoiding hitting other cars or obstacles, many of which are are stationary. > Not saying that speed is a factor, just that stopping distance isn't the thing. Of course it is. If you want to avoid crashing into another car, you have to maintain a safe distance. If your car is carrying too much kinetic energy, you can't dissipate the energy in advance of getting intimate with the other car, or a tree, or a center divider through which you roll your car uncontrollably. > Perhaps you should discuss kinetic energy instead? Say what? How did you miss the kinetic energy equation I included in the post to which you're replying? I even included the words "kinetic energy" to avoid any possible confusion.

by lutusp 13y ago

joosters 13y ago

Is that relevant? Most fatalities are not because the car drove straight into a stationary object directly in front of them on the road. So, total stopping distance doesn't come into play as you describe it. Collisions mostly happen because of the actions of car drivers who are going roughly the same speed as you. Not saying that speed is a factor, just that stopping distance isn't the thing. Perhaps you should discuss kinetic energy instead?

jakobe 13y ago
Stopping distance is extremely important. Here are a few examples of typical car accidents: - a driver in foggy weather crashes into a traffic jam - a car crosses an intersection at a red light, is hit by a car from the other direction - car hits a child running on the street - driver looses control, hits a tree at 60mph - reckless driver tries to overtake, hits car coming their way These types of accidents are the most lethal, and they are all due to stopping distance (and could be avoided by driving at a lower speed)
- lutusp 13y ago
  > - a driver in foggy weather crashes into a traffic jam This is a particularly dangerous and often misunderstood case, because staying several car lengths away from the car ahead won't do any good if that car suddenly collides with a stationary car in front of it that's hidden by the fog. When the car you're following comes to a sudden stop, all the rules about safe following distance go right out the window. This is why professionals sometimes recommend just getting off the road when fog prevents a reasonable amount of visibility. > These types of accidents are the most lethal, and they are all due to stopping distance (and could be avoided by driving at a lower speed) Very true.
lutusp 13y ago
> Is that relevant? Only when a misjudgment of stopping distance is a factor, in one way or another. I'll bet that the car driven by actor Paul Walker's friend -- the car that crashed and killed both of them -- was an example where the friend thought he had enough distance for a safe stop. But at the estimated speed -- "more than 100 MPH" -- more than 500 feet would have been required and just wasn't there, before a sharp turn they didn't manage. > Most fatalities are not because the car drove straight into a stationary object directly in front of them on the road. Yes, but all such accidents involve cars hitting each other or objects along the road, or rolling over during efforts to stop them, and similar causes. All these examples involve energy management, and in each case, the driver couldn't safely dissipate the car's kinetic energy. > Collisions mostly happen because of the actions of car drivers who are going roughly the same speed as you. Not in any number of cases, like crossing over the center divider, or hitting a roadside object, or losing control in bad weather, or fog collisions, etc. etc.. And even if two cars have a relatively low-speed collision while both traveling at high speed, then the problem becomes controlling the cars after the collision and avoiding hitting other cars or obstacles, many of which are are stationary. > Not saying that speed is a factor, just that stopping distance isn't the thing. Of course it is. If you want to avoid crashing into another car, you have to maintain a safe distance. If your car is carrying too much kinetic energy, you can't dissipate the energy in advance of getting intimate with the other car, or a tree, or a center divider through which you roll your car uncontrollably. > Perhaps you should discuss kinetic energy instead? Say what? How did you miss the kinetic energy equation I included in the post to which you're replying? I even included the words "kinetic energy" to avoid any possible confusion.