Originally Posted by Thrakos
Not entirely correct; It is a combination of inattention / driver distraction / driver impairment / inexperience and speed that cause collisions and crashes.
Remember, though, that the higher the speed, the less time you have to react. The average perception/reaction time for humans is 1.5seconds - for driving, we can break that down to 0.75s to perceive "trouble" and 0.75s to react to it; the higher the speed, the further you will have traveled in that 1.5 seconds. This of course can translate into a more severe crash/collision when something might have been avoidable all together.
(Yes, many other factors come into play (environmental / driver / vehicle condition(s)), but suffice it to say that speed is a factor... (though never the sole factor))
Your 2nd point is nonsensical. Are you suggesting that an absence of speed limits would reduce congestion?
The statistics speak for themselves. The amount of speed induced accidents are so low they are not worth mentioning. Yes it is possible that excessive speed could be a factor in an accident. I was referring more to what is actually happening on the roads though, and in that light, speeding is not even a factor worth looking at.
The speed limit itself does cause congestion. That's a bit bold, as congestion is more a factor of people not driving in their correct lane. But if you have vehicles in both lanes, one travelling say 68km/h, and the other trying to pass at 72km/h(both drivers may think they are travelling at the 70km/h speed limit according to their speedo). Then you have vehicles behind them travelling at 75km/h. Suddenly you have a huge congestion problem.
With the absence of a speed limit(or a reasonably set speed limit that was an actual maximum and not the expected rate of travel), slower vehicles would move right, and faster vehicle would filter though and reduce congestion.