stevei wrote:
SafeSpeed wrote:
stevei wrote:
The HGV 40 limit may have contributed to it, but it doesn't sound like it caused it. It sounds like the cause was an impatient driver overtaking at an inappropriate time rather than calmly driving along at 40 mph.
In an individual case you'll always be right.
However if we could look at national statistics another picture will be emerging. I'd feel comfortable calling the changes cause and effect.
Be careful, though, that is dangerously close to being the opposite of the argument that shows speeding to not cause accidents. Speeding is very common, yet accidents very rare, so speeding cannot be said to cause accidents. HGVs adhering to the 40mph limit are very common, yet accidents are very rare, so HGVs travelling at 40mph cannot be said to cause accidents. Except you're saying they do, which would imply you would have to accept the same can be true for speeding. I'd rather go for the more obvious and direct cause which is an inappropriate overtaking move - I'd hazard a guess that such action leads to an accident in a far greater proportion of cases than the act of driving an HGV at 40mph.
Perhaps you're right to highlight that 'speeding does not cause accidents' is fundamentally a weak argument. The way I see it, we should always be looking for policies where the (real world) benefits outweigh the disadvantages and side effects.
I am certain that the side effects of modern speed enforcement are far greater than the benefit (+potential benefits). I also think the side effects of HGV40 are far worse than the benefits.
Returning to the 'speeding does not cause accidents' statement, we're really looking at quantifying the small potential benefits of speed camera policy. This observation helps us to put the potential benefit in context. i.e. if few crashes have speeding as a cause or contributory factor then the potential benefit of eliminating speeding must be small.
Then there's the other thing we were talking about recently. We compared the large incidence of speeding in normal driving with the small incidence of excessive speed in crashes. I don't take the large ratio as lack of evidence of causation - rather I take the large ratio as evidence of different populations. (i.e. speeding does not take place where and when crashes are likely)
Bottom line: "speeding does not cause accidents" is a simplified argument.