What's a safe speed limit?

brianman · Jul 9, 2014

Alexander said:
Although the speed limit is 65, everyone consistently drives 75 to 80 mph. If your driving the speed limit on that section of the 14 freeway, you're actually a hazard. It's the only freeway I know where the CHP won't pull you over unless your going more then 20 mph over the limit. Simply because EVERYONE is driving that fast.

A certain Canadian video comes to mind....

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jerry33 said:
Because they're going 20 mph over the speed limit, they likely don't have the sight distance required to have even a reasonable chance of avoiding anything like a stopped car. Speed limits aren't just for revenue enhancement--although some are, and those train drivers to ignore the speed limits.

If it's not unsafe to have most drivers at 10mph over the posted limit, then the posted limit is wrong.
If it is unsafe to have most drivers at 10mph over the posted limit, then the lackluster enforcement is wrong.

In short, no matter what the drivers are doing the governing and/or policing bodies are incorrect in at least one way.

JRP3 · Jul 10, 2014

The problem is no matter what the posted limit reducing it by 10 mph would always be "safer". "Safe" is relative.

NoMoGas · Jul 10, 2014

At the risk of stating the obvious, posted speed limits are the ABSOLUTE MAXIMUM speed permitted by law. Period. There is no exception for flow of traffic, how far over we can get away with etc. It is sheer nonsense to say it's unsafe to drive the limit so I must speed faster then the limit. Trucks and trailers are capped in California at 55 which can be 15 slower then cars posted limits, works out just fine. If you want to speed just own it, we all do it. But if you're doing 70 and someone flies up behind you at 80, it's a 10mph differential not a justification to speed.

The fun and games end when someone gets hurt or killed. Trust me if you are doing 20 over the limit (reckless driving in ca) and end up in a fatal wreck you will be charged with vehicular manslaughter. So instead of manufacturing reasons to speed, just slide out of the fast lane and let the morons pass.

scaesare · Jul 10, 2014

jerry33 said:
Because they're going 20 mph over the speed limit, they likely don't have the sight distance required to have even a reasonable chance of avoiding anything like a stopped car. Speed limits aren't just for revenue enhancement--although some are, and those train drivers to ignore the speed limits.

Without conjecturing about the driver going over the limit (as far as I know we have no data on this), I will say that even at 55MPH and with clear sightlines and plenty of distance, if the car was "immobilized", as the earlier post suggested, this may have caught the driver by surprise.

The reason I say this is because that may mean the Toyota was slowing down without brake lights. If a car rapidly decelerates (or indeed is stopped) on a highway where there's no obvious obstruction in front of him, and there's no brake lights visible, it can be hard to recognize the driver in front of you is not moving all of the sudden. This can be exacerbated if a car in front of you changes out of the lane at the last second, and you have only a short time to assess the situation.

I've had it happen to me, and I tend to try to give myself adequate following distance, although here in the NoVA region outside of DC that is a challenge...

brianman · Jul 10, 2014

JRP3 said:
The problem is no matter what the posted limit reducing it by 10 mph would always be "safer". "Safe" is relative.

No, it won't. Especially from 0 to -10.

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NoMoGas said:
At the risk of stating the obvious, posted speed limits are the ABSOLUTE MAXIMUM speed permitted by law. Period.

No, it's not. If the law isn't enforced, in some senses it does not exist. (I'll stop there before we get into national politics.)

Lloyd · Jul 10, 2014

From NMA

rabar10 · Jul 10, 2014

JRP3 said:
The problem is no matter what the posted limit reducing it by 10 mph would always be "safer". "Safe" is relative.

brianman said:
No, it won't. Especially from 0 to -10.

brianman · Jul 10, 2014

The first sentence wasn't being pedantic, though I'll admit the second was a humor attempt that could come off as such.

Suppose the speed limit is 30mph and people are driving 40mph because the road really should have a higher limit in the opinions of the populace. If you drop that to 20mph, I would argue you've created a more hazardous situation rather than less. One of the reasons is that some drivers will stick to the limit of 20 which creates an even bigger gap between the "rigorous law abiders" and the natural driving speed of others.

It also means that some people going 40 will now slam on the brakes to drop to 20 when they (think they) see an officer nearby. Compare this with dropping from 40 to 30 from the perspective of the cars behind them.

dsm363 · Jul 10, 2014

By and large though when someone says something fairly obvious and any reasonable person knows what they are talking about you can reasonably assume they mean what they say. If you think you may be misreading it, send a PM. Of course going from 0 to -10 wouldn't be safer. No one would ever suggest that but the main point of slower being safer in a wreck stands.

brianman · Jul 10, 2014

dsm363 said:
but the main point of slower being safer in a wreck stands.

Okay now I'm really confused. Perhaps I misread, but I thought JRP was talking about the impact of lowering the posted speed limit not on the difference in damage (human and metal) at various speeds of wrecks.

dsm363 · Jul 10, 2014

brianman said:
Okay now I'm really confused. Perhaps I misread, but I thought JRP was talking about the impact of lowering the posted speed limit not on the difference in damage (human and metal) at various speeds of wrecks.

Well if speed limit is 40 and people obey it a crash is more severe than if it is 30 and people obey it. People don't obey it though.

ACDriveMotor · Jul 10, 2014

I would submit that crashes aren't safe, period. People can be injured or die in relatively low closing velocity crashes regardless of the absolute value of posted speed limits. It is the dV that matters in the relevant physics.

http://www.nhtsa.gov/people/injury/enforce/speed_forum_presentations/ferguson.pdf

JRP3 · Jul 10, 2014

Let's face it, if the posted speed limit was 20 mph and enforced within a 10 mph range few would ever die or be injured in modern vehicles. Not saying this is realistic or desirable.

brianman · Jul 10, 2014

JRP3 said:
Let's face it, if the posted speed limit was 20 mph and enforced within a 10 mph range few would ever die or be injured in modern vehicles. Not saying this is realistic or desirable.

Right, because the street would be either conjested (and the police force exhausted) OR the street would be completely unused because it would be comically inefficient.

JRP3 · Jul 10, 2014

Government mandated electronic speed control would eliminate the need for enforcement. Limit pack voltage to 48V and current to 400 amps, make vehicle bodywork the consistency of marshmallows. (Again, not realistic or desirable.) What is your counter argument, that higher speeds are really safer?

bonnie · Jul 10, 2014

Is it REALLY that hard to stay on topic? Or are you all just taking pride in how fast you can derail things?

brianman · Jul 10, 2014

JRP3 said:
Government mandated electronic speed control would eliminate the need for enforcement. Limit pack voltage to 48V and current to 400 amps, make vehicle bodywork the consistency of marshmallows. (Again, not realistic or desirable.) What is your counter argument, that higher speeds are really safer?

And there we are. That didn't take long. Not in this country please. I can think a lot of other countries where such an approach would be more appropriate.

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bonnie said:
Is it REALLY that hard to stay on topic? Or are you all just taking pride in how fast you can derail things?

Give it two more posts, and we'll be discussing the impact of CC (climate change) on ACC (adaptive cruise control). They show up in every thread anyway.

NigelM · Jul 10, 2014

bonnie said:
Is it REALLY that hard to stay on topic? Or are you all just taking pride in how fast you can derail things?

~15 posts on speed limits....I carved it out into this thread.

JRP3 · Jul 11, 2014

bonnie said:
Is it REALLY that hard to stay on topic? Or are you all just taking pride in how fast you can derail things?

Active minds wander freely.

ACDriveMotor · Jul 11, 2014

Since this is now a thread about safe speed the discussion is re-railed (un-derailed?) apparently.

What's a safe speed limit?

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