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Respectfully, I did, and you're failing to acknowledge what I wrote in my initial posting. > it is saying that speed differential is more dangerous than speed

Respectfully, I did, and you're failing to acknowledge what I wrote in my initial posting. > it is saying that speed differential is more dangerous than speed. No it's not, the article is saying that a delta in speed is a factor in crash frequency. (And no, I didn't copy paste the whole abstract, because I was posting the part of the abstract germane to the quote I cited from the original article.) > This is a horrible starting model. The severity of crashes is physics, but the frequency can't be looked at in isolation. No, it's still a good starting model. If you read all the way to the end of that abstract, I think you'll see my point: > Without exception, a vehicle that moved (much) faster than other traffic around it, had a higher crash rate. With regard to the rate of a (much) slower moving vehicle, the evidence is inconclusive. So, much faster moving vehicles always had higher crash rates, while much slower vehicles... inconclusive. There's a saying in statistics (George Box) that all models are wrong, but some models are useful. I think you'll find examples where speed isn't a problem, but those aren't the norm. If you're looking for a simple univariate model that goes a good long ways toward explaining vehicle safety, I'd challenge you to come up with a better one than what I've proposed here.

Ygg2 12y ago
> Without exception, a vehicle that moved (much) faster than other traffic around it, Emphasis mine. Your slower moving vehicle could relate to vehicles moving slower than other cars. Which is what gp claimed.
nyc640 12y ago
The article isn't claiming that faster speed == safer. It clearly states that raising the speed limit has little effect on the speed that most people travel. The only group of people whose driving speed it significantly affects is the 10% of people who follow the speed limit exactly (who are usually the slowest drivers). Therefore, by raising the speed limit, a large majority of drivers will drive at the same speed (no faster), but the slowest drivers will speed up and the speed differential drops, making the roads safer, as your linked article agrees with. There was little evidence presented that justified the assumption that most people won't drive any faster with a raised speed limit, but if we take that as true, then its conclusion is consistent with the research you linked. It is NOT making the claim that driving faster is safer. In fact, it again clearly states that in an ideal world, everybody would just travel at slower and safer speeds, but that we can't effectively enforce such a low speed limit.
cbsmith 12y ago
As the article states, the 85th percentile rule is as old as the hills, and the principle about speed differential is as well. All the data I've ever seen would appear to support it. Do you have any theories as to why states with higher speed limits (or in Montana's case, no speed limits) don't have terribly different worse outcomes from those that have lower ones?

Ygg2 12y ago

> Without exception, a vehicle that moved (much) faster than other traffic around it, Emphasis mine. Your slower moving vehicle could relate to vehicles moving slower than other cars. Which is what gp claimed.

nyc640 12y ago

The article isn't claiming that faster speed == safer. It clearly states that raising the speed limit has little effect on the speed that most people travel. The only group of people whose driving speed it significantly affects is the 10% of people who follow the speed limit exactly (who are usually the slowest drivers). Therefore, by raising the speed limit, a large majority of drivers will drive at the same speed (no faster), but the slowest drivers will speed up and the speed differential drops, making the roads safer, as your linked article agrees with. There was little evidence presented that justified the assumption that most people won't drive any faster with a raised speed limit, but if we take that as true, then its conclusion is consistent with the research you linked. It is NOT making the claim that driving faster is safer. In fact, it again clearly states that in an ideal world, everybody would just travel at slower and safer speeds, but that we can't effectively enforce such a low speed limit.

cbsmith 12y ago

As the article states, the 85th percentile rule is as old as the hills, and the principle about speed differential is as well. All the data I've ever seen would appear to support it. Do you have any theories as to why states with higher speed limits (or in Montana's case, no speed limits) don't have terribly different worse outcomes from those that have lower ones?