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Is Every Speed Limit Too Low?

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Re: Is Every Speed Limit Too Low?

#11

Post by colanderman »

_archon_ wrote: post #4

I found myself disagreeing with the premise that highway speed limits don't influence people's driving speed. I may simply be part of the 15%, but consider the following anecdata: On I-90 in upstate NY, the "speed limit" is 65. I've gone by several state troopers at 70-75 without issue or confrontation. I don't go faster, not because traffic dictates, but I'm concerned about litigious policemen. To put it in Freakono…

It's not an arbitrary premise, it's studied:

“Over the years, I’ve done many follow up studies after we raise or lower a speed limit,” Megge tells us. “Almost every time, the 85th percentile speed doesn’t change, or if it does, it’s by about 2 or 3 mph.”

Re: Is Every Speed Limit Too Low?

#12

Post by astral303 »

colanderman wrote: post #11
_archon_ wrote: post #4

I found myself disagreeing with the premise that highway speed limits don't influence people's driving speed. I may simply be part of the 15%, but consider the following anecdata: On I-90 in upstate NY, the "speed limit" is 65. I've gone by several state troopers at 70-75 without issue or confrontation. I don't go faster, not because traffic dictates, but I'm concerned about litigious policemen. To put it in Freakono…

It's not an arbitrary premise, it's studied: “Over the years, I’ve done many follow up studies after we raise or lower a speed limit,” Megge tells us. “Almost every time, the 85th percentile speed doesn’t change, or if it does, it’s by about 2 or 3 mph.”

Thank you for the scientific backup.

Re: Is Every Speed Limit Too Low?

#13

Post by _archon_ »

colanderman wrote: post #11
_archon_ wrote: post #4

I found myself disagreeing with the premise that highway speed limits don't influence people's driving speed. I may simply be part of the 15%, but consider the following anecdata: On I-90 in upstate NY, the "speed limit" is 65. I've gone by several state troopers at 70-75 without issue or confrontation. I don't go faster, not because traffic dictates, but I'm concerned about litigious policemen. To put it in Freakono…

It's not an arbitrary premise, it's studied: “Over the years, I’ve done many follow up studies after we raise or lower a speed limit,” Megge tells us. “Almost every time, the 85th percentile speed doesn’t change, or if it does, it’s by about 2 or 3 mph.”

Yes, according to that article. What I'm driving at is that making an arbitrary change based on how drivers react to an improper restriction may in fact lead to imposing another improper and arbitrary restriction. A change of 5 mph either way won't change anything fundamental, and so a traffic study will report minimal changes.

Re: Is Every Speed Limit Too Low?

#14

Post by arthurdenture »

wahsd wrote: post #7
Symmetry wrote: post #3

Their reasoning about the dangers of low speed limits make a lot of sense when you're looking at highways, but I don't think they'd necessarily apply to city or residential streets where there are frequent red lights, pedestrians, etc. Of course, the right thing to do there is probably to configure the roads so that people drive more slowly naturally by narrowing lanes, having trees on the side of the road, etc.

It doesn't even make any sense regarding highways. Ignoring their embarrassingly flawed standard for setting speed limits based on a percentile of speed limited traffic, there are so many other factors that go into the danger of traffic that are wholly and totally separate from speed. I would argue that the speed is exponentially less significant than the skill and training and experience of the drivers. Take a compa…

> The USA's per capita automobile death rate is over twice as high as Germany's, in spite of speed limits in general being lower in Germany and there being far more and more generous roads in the USA. [...] Statistically speaking though, you would think that more driving on wider, bigger roads and in less densely populated areas would lead to less accidents and not more.

The relationship between forgiving roads and safety does not necessarily run in the direction you assume. People generally drive at a speed that feels safe, so a road that feels safe will have faster speeds. Faster speeds don't necessarily lead to more crashes, but they definitely lead to a higher rate of serious injuries and fatalities.

Given a difference in fatality rate between two developed countries, I'd definitely look at factors like traffic engineering before jumping to the conclusion that, say, Americans are just worse drivers than Germans.

Re: Is Every Speed Limit Too Low?

#15

Post by peatmoss »

This article ignores a lot of peer-reviewed literature from planning, public health / injury prevention, and civil engineering in favor of some folksy wisdom of a lieutenant cop. A good starting mental model is that vehicle speeds increase both the frequency and severity of crashes.

The article weakly, and quietly made an argument that I do agree with. Namely, roadway design needs to accompany speed limits to ensure people actually drive the desired speeds. Wide lanes, big setbacks, homogenous environments encourage speeding regardless of what is posted. But let's be clear, we should have our design follow our policy, not our policy follow bad designs that were put in place by roadway engineers of yesteryear.

That message seemed to be lost in the race to tell us something tantalizingly counterintuitive. I love "everything we know is wrong" storytelling as much as the next guy, but only when that's actually backed up with solid evidence. Take for example this gem from the article:

> “We all speed, yet months and months usually pass between us seeing a crash,” Lt. Megge tells us when we call to discuss speed limits. “That tells me that most of us are adequate, safe, reasonable drivers. Speeding and traffic safety have a small correlation.”

That would seem to be at odds with this peer reviewed article (sorry, paywall, but you can read the abstract):

> Respectively, they found evidence for an exponential function and a power function between speed and crash rate. Both types of studies found evidence that crash rate increases faster with an increase in speed on minor roads than on major roads. At a more detailed level, lane width, junction density, and traffic flow were found to interact with the speed–crash rate relation.

Link to article: http://www.sciencedirect.com/science/article/pii/S0001457505...

Priceonomics's banner ad tells me it is selling a new book titled "Everything is Bullshit." Quite right.

Re: Is Every Speed Limit Too Low?

#16

Post by mikeash »

_archon_ wrote: post #4

I found myself disagreeing with the premise that highway speed limits don't influence people's driving speed. I may simply be part of the 15%, but consider the following anecdata: On I-90 in upstate NY, the "speed limit" is 65. I've gone by several state troopers at 70-75 without issue or confrontation. I don't go faster, not because traffic dictates, but I'm concerned about litigious policemen. To put it in Freakono…

Here's some support from a different direction.

Starting a couple of years ago, Virginia started bumping up the speed limit on the more rural sections of interstates from 65 to 70MPH. Part of the stated rationale was that a lot of people speed anyway, but a lot of other people drive the speed limit, and this disparity is dangerous. By bumping up the limit, you're in essence telling the law-abiding drivers "it's OK to keep up with traffic" and the gap in speeds will narrow.

In my experience, the opposite happened. It seems that the people who were driving 65 before don't want to go any faster. The people who were speeding before still constrained their speed to some factor above the speed limit, and now they go even faster still. Previously, the spread was around 65-75, now it's more like 65-80.

In contrast, the interstates around DC are all limited to 55, yet people regularly do 70 there as well.

It seems clear to me that, while speed limits don't impose an iron control on vehicle speeds, they do influence it.

A sibling poster mentions studies that say it changes little if at all. Perhaps what's "clear" to me isn't true. However, I wonder just how those studies were performed. How long did they wait after the changed limit to measure the change in speed? Most traffic on most roads consists of people who make the trip regularly, and it will take time for them to change their habits, up or down.

Re: Is Every Speed Limit Too Low?

#17

Post by nostromo »

wahsd wrote: post #7
Symmetry wrote: post #3

Their reasoning about the dangers of low speed limits make a lot of sense when you're looking at highways, but I don't think they'd necessarily apply to city or residential streets where there are frequent red lights, pedestrians, etc. Of course, the right thing to do there is probably to configure the roads so that people drive more slowly naturally by narrowing lanes, having trees on the side of the road, etc.

It doesn't even make any sense regarding highways. Ignoring their embarrassingly flawed standard for setting speed limits based on a percentile of speed limited traffic, there are so many other factors that go into the danger of traffic that are wholly and totally separate from speed. I would argue that the speed is exponentially less significant than the skill and training and experience of the drivers. Take a compa…

Per-capita is a bad way of measuring auto-fatalities.

The US is very spread out and requires a lot of driving. For example, just driving from SF to LA requires more driving than Cologne to Berlin.

Per mile driven is much better, and it narrows the US gap with other countries substantially. (The US is slightly lower than Japan, slightly higher than France.)

Re: Is Every Speed Limit Too Low?

#18

Post by tux1968 »

peatmoss wrote: post #15

This article ignores a lot of peer-reviewed literature from planning, public health / injury prevention, and civil engineering in favor of some folksy wisdom of a lieutenant cop. A good starting mental model is that vehicle speeds increase both the frequency and severity of crashes. The article weakly, and quietly made an argument that I do agree with. Namely, roadway design needs to accompany speed limits to ensure…

There is conflicting evidence on the matter. A local (Vancouver) video[1] circulating here had some strong arguments that our speed limits are kept needlessly low. If you're interested in such things, it's a well done video and worth the 15 minutes it takes to watch.

[1] http://www.vancitybuzz.com/2013/09/speed-does-not-kill-vanco...

Re: Is Every Speed Limit Too Low?

#19

Post by tunesmith »

Raising the speed limit to the 85%/15% ratio isn't necessarily the safest way to handle the driving. If there's a road where more than 15% of drivers are going faster than the speed limit, one option is to raise the speed limit, but the other option is to change the road so people won't drive so fast on it.

Re: Is Every Speed Limit Too Low?

#20

Post by colanderman »

wahsd wrote: post #7
Symmetry wrote: post #3

Their reasoning about the dangers of low speed limits make a lot of sense when you're looking at highways, but I don't think they'd necessarily apply to city or residential streets where there are frequent red lights, pedestrians, etc. Of course, the right thing to do there is probably to configure the roads so that people drive more slowly naturally by narrowing lanes, having trees on the side of the road, etc.

It doesn't even make any sense regarding highways. Ignoring their embarrassingly flawed standard for setting speed limits based on a percentile of speed limited traffic, there are so many other factors that go into the danger of traffic that are wholly and totally separate from speed. I would argue that the speed is exponentially less significant than the skill and training and experience of the drivers. Take a compa…

I don't think you're disagreeing with the article's premise. Your "horrible drivers" can include people who either drive far too fast or far too slow, thus creating a speed differential. Lt. Megge's idea concedes that you can't get the fast drivers to slow down, but maybe you can get the slow drivers to speed up.

(Aside, I agree 100% about more rigorous licensing. I spend 3 hrs on the highway each day; easily 80% of the drivers I see are utterly incompetent: texting, driving slow in the left lane, passing on the right, lights off at night, falling asleep, etc. Heck, I saw one driver eating out of a bowl with both hands.)

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