Should cars have built-in speed limit?

Phys251 said:

That's not necessarily true and I can prove it. Here is a counterexample. Quote:

"GDOT officials are considering raising the speed limit to 70 in urban areas - or places with populations of 50,000 or more. The agency raised the speed limit to 65 mph along a 27-mile stretch of I-285 in November. Department records show that drivers traveled at 65.4 mph after the limit was raised, compared with 65.5 mph from before. The limit had been 55 mph."​

My preliminary research suggests that raising speed limits on interstates, particularly rural interstates, can be a reasonable course of action (PDF). But raising speed limits on surface streets is not:

The results of the model estimations showed that, for the speed limit ranges currently used, speed limits did not have a statistically significant effect on the severity of accidents on Interstate highways. However, for some non-Interstate highways, higher speed limits were found to be associated with higher accident severities, suggesting that
future speed limit changes, on non-Interstate highways in particular, need to be carefully assessed on a case-by-case basis.​

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That doesn't prove anything since we don't know what stretch of road they're talking about or what it looks like. I specifically said "unless the road is obviously hazardous at those higher speeds". For example, few people will drive 80 MPH on a hilly 2-lane even if the speed limit is set to 90 MPH. Most drivers have at least some sense of what's safe and what isn't. Since the average speed driven didn't change in this case, that tells me the State finally got the speed limit right. It in no way implies that all or even most interstates are signed correctly or that higher posted limits won't result in higher average speeds.


It all depends on what the limit was before the change. I can certainly show that 55 MPH was safer than the (mish-mash but) higher speed limits we have now. That's ancient history at this point. The percent of speeders was higher at 55 (because drivers knew it was low-balled) but the fatality rate was lower.


PS

A survey of Indiana drivers in the fall of 2005 (a few months after Indiana Interstate speed limits were raised) found that under free-flow conditions, drivers reported driving an average of nearly 11 mph over a 55-mph Interstate speed limit, about 9 mph over a 65-mph Interstate speed limit, and less than 8 mph over a 70-mph speed limit (27).

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Your own study proves my case. Average speeds all of them over the speed limit went up with higher speed limits:

55/66
65/74
70/77

DVSentinel said:

Enjoy the read. But I am not going re-address points already made. Or don't and just let everyone know that you are only interested in being antagonistic and don't really have a point to make.

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I'm not. I'm simply asking for a post number, because I don't feel like searching through nearly 300 posts. Or are you bluffing?

MoSurveyor said:

That doesn't prove anything since we don't know what stretch of road they're talking about or what it looks like. I specifically said "unless the road is obviously hazardous at those higher speeds". For example, few people will drive 80 MPH on a hilly 2-lane even if the speed limit is set to 90 MPH. Most drivers have at least some sense of what's safe and what isn't. Since the average speed driven didn't change in this case, that tells me the State finally got the speed limit right. It in no way implies that all or even most interstates are signed correctly or that higher posted limits won't result in higher average speeds.

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I don't think it has much at all to do with what drivers perceive as safe. If they can show me that they can solve complicated physics equations in their head, in like, three seconds, then maybe I'll believe the line that an individual inherently knows what's safe on the road. The bottom line is that the maximum safe speed, whatever it may be, is a result of a mathematical function, not a personal perception.

It all depends on what the limit was before the change. I can certainly show that 55 MPH was safer than the (mish-mash but) higher speed limits we have now. That's ancient history at this point. The percent of speeders was higher at 55 (because drivers knew it was low-balled) but the fatality rate was lower.

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That makes sense. People, some in particular, don't want to admit that in general, slower driving = safer driving. The notion that it's the speed differential and not the aggregate speed is a myth. But the trick is to find the right balance between safety and speed.

PS
Your own study proves my case. Average speeds all of them over the speed limit went up with higher speed limits:

55/66
65/74
70/77

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Different strokes for different folks. If that turns out to be the dominant trend, then that is a reason to keep highway speed limits LOW and enforce them hard.

jmotivator said:

An Experiment: Push the gas pedal all the way down while you are on the highway... I would suggest you will find your car already has a speed limit. :rock

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Any tech data to support that? Short of just not going any faster most cars to not have a top speed limiter.

How about we just ban cars altogether. No cars, no car deaths.

Phys251 said:

I'm not. I'm simply asking for a post number, because I don't feel like searching through nearly 300 posts. Or are you bluffing?

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No, not bluffing. You want me to give you that information because you don't want to go back and read the post. Well, I would have to go back and reread them to get that information. I don't want to do that.

CRUE CAB said:

Any tech data to support that? Short of just not going any faster most cars to not have a top speed limiter.

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First, lighten up, it's a joke..

Secondly, it is simple physics. As a car increases in speed the wind resistance pressing in the opposite direction also increases. When the wind resistance equals the car's power output (/w gravity assist) the car will stop accelerating and reach it's speed limit.

jmotivator said:

First, lighten up, it's a joke..

Secondly, it is simple physics. As a car increases in speed the wind resistance pressing in the opposite direction also increases. When the wind resistance equals the car's power output (/w gravity assist) the car will stop accelerating and reach it's speed limit.

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Drag, not wind resistance is the greater force.

DVSentinel said:

Drag, not wind resistance is the greater force.

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Yeah, sorry for the careless post. Either way, the joke has been officially killed via analysis.

DVSentinel said:

No, not bluffing. You want me to give you that information because you don't want to go back and read the post. Well, I would have to go back and reread them to get that information. I don't want to do that.

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Exactly what I thought. You have nothing. Next!

Phys251 said:

I don't think it has much at all to do with what drivers perceive as safe. If they can show me that they can solve complicated physics equations in their head, in like, three seconds, then maybe I'll believe the line that an individual inherently knows what's safe on the road. The bottom line is that the maximum safe speed, whatever it may be, is a result of a mathematical function, not a personal perception.

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You can certainly put it in terms of mathematics but you'd have to measure people's reaction times in various circumstances and conditions; you'd have to measure each cars responses in steering, suspension, braking, acceleration, etc, etc and update them all as components wear and maintenance is done; you'd have to mark every single section of road to show it's design speed - and a thousands other little things that drivers adjust to everyday just from overall driving experience as well as experience with their vehicle.

A gymnast doesn't do Newtonian physics in their head when they do a routine on the parallel bars or whatever. They know what their body can do and they do it. Driving is the same way. Spend all your time actually thinking about driving and you'll be paying more attention to your thoughts than to the actual act of driving. What nonsense! You know how far you can see, you can feel the road through the wheel, you feel the slight drift and response of the car from moment to moment - all sorts of little clues that let you know what is and isn't safe and most of them unconscious, just like any other physical endeavor.

Phys251 said:

That makes sense. People, some in particular, don't want to admit that in general, slower driving = safer driving. The notion that it's the speed differential and not the aggregate speed is a myth. But the trick is to find the right balance between safety and speed.

Different strokes for different folks. If that turns out to be the dominant trend, then that is a reason to keep highway speed limits LOW and enforce them hard.

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According to the traffic engineers I've talked to, that is the trend, and I've seen it in various studies (like the one you linked), as well. It's why I take the position I do when it comes to speeding. (There are even some situations where I slow down below the average speed because I see a hazard most others apparently don't.) If you push enforcement too much you create problems. If you low-ball the speed limit too much you create problems. Traffic engineers and law enforcement do a balancing act to keep traffic flowing as fast and safe as they can. I don't often question their signage but I do ignore it sometimes and just pay the fine if I'm caught - no harm, no foul.

MoSurveyor said:

You can certainly put it in terms of mathematics but you'd have to measure people's reaction times in various circumstances and conditions; you'd have to measure each cars responses in steering, suspension, braking, acceleration, etc, etc and update them all as components wear and maintenance is done; you'd have to mark every single section of road to show it's design speed - and a thousands other little things that drivers adjust to everyday just from overall driving experience as well as experience with their vehicle.

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All of which are excellent reasons why we shouldn't necessarily leave people to their own devices. Even if they can somehow, by some miracle, solve a multivariate function in their heads within a fraction of a second, then there are the psychological and physiological factors: Confirmation bias. Cultural expectations. Distractions. Alcohol. Hell, when you think of it in these terms, one wonders why the national speed limit isn't 20 miles per hour.

A gymnast doesn't do Newtonian physics in their head when they do a routine on the parallel bars or whatever. They know what their body can do and they do it. Driving is the same way. Spend all your time actually thinking about driving and you'll be paying more attention to your thoughts than to the actual act of driving. What nonsense! You know how far you can see, you can feel the road through the wheel, you feel the slight drift and response of the car from moment to moment - all sorts of little clues that let you know what is and isn't safe and most of them unconscious, just like any other physical endeavor.

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Bad analogy. First of all, gymnastics is a spectacularly dangerous sport. Secondly, I am not aware of a single instance of any of those horrific gymnastics injuries that injured an innocent bystander--and if they have occurred, I bet that they are extremely rare. Third, if you want to solve all the physics equations that correspond to this:


Including margin of error (which is why this was such a spectacular vault!), then be my guest. Take as much time as you need.

According to the traffic engineers I've talked to, that is the trend, and I've seen it in various studies (like the one you linked), as well. It's why I take the position I do when it comes to speeding. (There are even some situations where I slow down below the average speed because I see a hazard most others apparently don't.) If you push enforcement too much you create problems. If you low-ball the speed limit too much you create problems. Traffic engineers and law enforcement do a balancing act to keep traffic flowing as fast and safe as they can. I don't often question their signage but I do ignore it sometimes and just pay the fine if I'm caught - no harm, no foul.

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Do you realize that you are inadvertently making an argument for keeping speed limits low and strictly enforcing them? I think we need to wake up and ask ourselves, as a nation, when is enough enough? When are we going to stop sacrificing 30,000+ people every year on the altar of reckless, careless, and otherwise dangerous driving? And no that does not immediately imply that speed = bad, and thus, less speed = good. We've got to be able to move from point A to point B. The question is what price we're willing to pay to do so.

Mathematician said:

I'm going to dodge the question and say we should hurry up and develop automobiles which run only on auto-pilot. This would solve the issue in the OP, plus a significant number of other problems.

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No more DUIs. People could go out and get drunk again, but this time with no fear of hurting or killing anyone, plus no fear of tickets and/or prosecution.

radcen said:

No more DUIs. People could go out and get drunk again, but this time with no fear of hurting or killing anyone, plus no fear of tickets and/or prosecution.

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Unless they vomit on the autopilot and it malfunctions.

Phys251 said:

All of which are excellent reasons why we shouldn't necessarily leave people to their own devices. Even if they can somehow, by some miracle, solve a multivariate function in their heads within a fraction of a second, then there are the psychological and physiological factors: Confirmation bias. Cultural expectations. Distractions. Alcohol. Hell, when you think of it in these terms, one wonders why the national speed limit isn't 20 miles per hour.

Bad analogy. First of all, gymnastics is a spectacularly dangerous sport. Secondly, I am not aware of a single instance of any of those horrific gymnastics injuries that injured an innocent bystander--and if they have occurred, I bet that they are extremely rare. Third, if you want to solve all the physics equations that correspond to this:

Including margin of error (which is why this was such a spectacular vault!), then be my guest. Take as much time as you need.

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The analogy was about solving equations for physical activities as opposed to just doing it by training your body and using your experience. Apparently you do everything by solving the motion equations, first - makes one wonder how you can even walk down the street. Do you actually have to constantly say to yourself, "I shouldn't go past the curb when there's traffic in the street"? :lol:

Phys251 said:

Do you realize that you are inadvertently making an argument for keeping speed limits low and strictly enforcing them?

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If that's what you're getting from my argument then you're not reading very well. I specifically stated "keep traffic flowing as fast and safe as they can." You seem to have missed that.

Phys251 said:

I think we need to wake up and ask ourselves, as a nation, when is enough enough? When are we going to stop sacrificing 30,000+ people every year on the altar of reckless, careless, and otherwise dangerous driving? And no that does not immediately imply that speed = bad, and thus, less speed = good. We've got to be able to move from point A to point B. The question is what price we're willing to pay to do so.

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We've made that choice, where have you been? How many years did you drive under the 55 MPH federal speed limit?

MoSurveyor said:

The analogy was about solving equations for physical activities as opposed to just doing it by training your body and using your experience. Apparently you do everything by solving the motion equations, first - makes one wonder how you can even walk down the street. Do you actually have to constantly say to yourself, "I shouldn't go past the curb when there's traffic in the street"? :lol:

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There are clear right-of-way rules for cars and pedestrians. One can choose to follow those rules or to take one's life or future in someone else's hand. For someone to make the case that such right-of-way laws need to be changed or do not deserve to be followed, fine, but the burden is on those who make this choice. Intuition or "I don't like it" is a terrible reason to flaunt a law. One needs to make a clear and convincing case. Demonstrating the appropriate use of mathematical functions would be a good start.

If that's what you're getting from my argument then you're not reading very well. I specifically stated "keep traffic flowing as fast and safe as they can." You seem to have missed that.

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No--your study implies that people, left to their own devices, will speed no matter what. So the only way to keep people from traveling at very fast speeds is to keep the speed limits down and to enforce them. Hint: This is not something I support doing.

BTW, my study showed different results. Maybe Atlanta drivers behave in a significantly different way than Indiana drivers do.

We've made that choice, where have you been? How many years did you drive under the 55 MPH federal speed limit?

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You do know why they lowered the speed limit to 55 for awhile, right? And nowhere did I imply that I favor returning to that. Personally I think that for rural interstates, 80-85 could be a reasonable speed limit under ideal conditions--smooth road, daytime, good visibility, no rain/snow, etc. It seems to work quite well all over Europe.

Phys251 said:

There are clear right-of-way rules for cars and pedestrians. One can choose to follow those rules or to take one's life or future in someone else's hand. For someone to make the case that such right-of-way laws need to be changed or do not deserve to be followed, fine, but the burden is on those who make this choice. Intuition or "I don't like it" is a terrible reason to flaunt a law. One needs to make a clear and convincing case. Demonstrating the appropriate use of mathematical functions would be a good start.

No--your study implies that people, left to their own devices, will speed no matter what. So the only way to keep people from traveling at very fast speeds is to keep the speed limits down and to enforce them. Hint: This is not something I support doing.

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Finally found what I've been looking for. The 85% is a standard reference for all streets and highways.

Speed limits should be determined by an Engineering and.Traffic Study of the street section involved. Of consideration in reviewing a speedlimit change should be the 85th percentile speed (at which 85% of the traffic is traveling slower than this speed), the location of sidewalks, driveways, obstructions, the horizontal and vertical alignment of the street, the use of the street by pedestrians and the existence of hazards which-are not easy to detect by drivers.

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Speed.
Drivers generally ignore posted speed limits, and travel at speeds which the “drivers consider reasonable, comfortable, convenient and safe under existing conditions. Drivers appear not to operate by the speedometer, but by the conditions they meet.

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http://www.ite.org/traffic/documents/Tcir0365b.pdf

ITE = Institute of Traffic Engineers

Phys251 said:

BTW, my study showed different results. Maybe Atlanta drivers behave in a significantly different way than Indiana drivers do.

You do know why they lowered the speed limit to 55 for awhile, right? And nowhere did I imply that I favor returning to that. Personally I think that for rural interstates, 80-85 could be a reasonable speed limit under ideal conditions--smooth road, daytime, good visibility, no rain/snow, etc. It seems to work quite well all over Europe.

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You referenced the Indiana study, not me. I just quoted numbers from it.

The Atlanta study just tells me they had the right speed limit to start with. You can't compare the two studies without knowing the exact conditions and specs on the roadways in question. We have no clue what the Atlanta road is/was like. The Indiana data is an average of many highways, a much better metric than one given section of highway.


I know why 55, I was there.

MoSurveyor said:

Finally found what I've been looking for. The 85% is a standard reference for all streets and highways.

http://www.ite.org/traffic/documents/Tcir0365b.pdf

ITE = Institute of Traffic Engineers

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Right, that's one of the standards that's supposed to be used to establish the speed limit. Honest question here: Is that 85th-percentile assumed to be constant when establishing the limit?

You referenced the Indiana study, not me. I just quoted numbers from it.

The Atlanta study just tells me they had the right speed limit to start with. You can't compare the two studies without knowing the exact conditions and specs on the roadways in question. We have no clue what the Atlanta road is/was like. The Indiana data is an average of many highways, a much better metric than one given section of highway.


I know why 55, I was there.

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Well I was there in Atlanta, so I guess that makes us even. Again, different strokes for different folks. Various people in different parts of the country have considerably different driving habits. How they react to changing speed limits may vary as well. That's why we need more information.

Built in speed limits? Maybe... as long as the car adjusts to the speed limit that you are in. Don't see how that is possible though. Otherwise, If you have a speed limit at 70mph for highways then you could drive 70 in a 30 zone and that defeats the purpose.

What they SHOULD have are built in breathalyzers that won't start engine unless you are under the limit...

Phys251 said:

Right, that's one of the standards that's supposed to be used to establish the speed limit. Honest question here: Is that 85th-percentile assumed to be constant when establishing the limit?

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I'm not sure I understand your question. Do all traffic engineers shoot for this percentile? As a base, yes, but that is adjusted by the other variables mentioned like side road access, sidewalks/pedestrian traffic, etc., etc.

Phys251 said:

Well I was there in Atlanta, so I guess that makes us even. Again, different strokes for different folks. Various people in different parts of the country have considerably different driving habits. How they react to changing speed limits may vary as well. That's why we need more information.

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Most traffic laws and safety practices in this country are universal - so what, exactly, do you mean?

Phys251 said:

All of which are excellent reasons why we shouldn't necessarily leave people to their own devices. Even if they can somehow, by some miracle, solve a multivariate function in their heads within a fraction of a second, then there are the psychological and physiological factors: Confirmation bias. Cultural expectations. Distractions. Alcohol. Hell, when you think of it in these terms, one wonders why the national speed limit isn't 20 miles per hour.



Bad analogy. First of all, gymnastics is a spectacularly dangerous sport. Secondly, I am not aware of a single instance of any of those horrific gymnastics injuries that injured an innocent bystander--and if they have occurred, I bet that they are extremely rare. Third, if you want to solve all the physics equations that correspond to this:

Including margin of error (which is why this was such a spectacular vault!), then be my guest. Take as much time as you need.




Do you realize that you are inadvertently making an argument for keeping speed limits low and strictly enforcing them? I think we need to wake up and ask ourselves, as a nation, when is enough enough? When are we going to stop sacrificing 30,000+ people every year on the altar of reckless, careless, and otherwise dangerous driving? And no that does not immediately imply that speed = bad, and thus, less speed = good. We've got to be able to move from point A to point B. The question is what price we're willing to pay to do so.

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The one irreplaceable commodity a person has it time. That is one thing think that can not be bought. But apparently time is irrelevant to you, that you put no value on your time whatsoever. If you have to sit in a box for 1, 2, 5, 10 hour, an extra 100 or 1000 0r 10,000 hours of your life so you are safe and poise no danger to others, you're all for it.

So, then, you now have justify anyone leaving their home without a compelling reason to do so. If they say in their homes they endanger no now. Endangering others is intolerable to you, right? Thus, a person leaving their house unless truly necessary should be considered criminal reckless endangerment to others.

MoSurveyor said:

Traffic engineering and enforcement doesn't work that way. If the speed limit is 70, X number of drivers will go +5 (75), a smaller number (Y) will go +10 (80), and a smaller number still (Z) will go faster than +10 (81+). When you raise the speed limit - say to 75 - those numbers don't drop much unless the road is obviously hazardous at those higher speeds. There will still be X, Y, and Z number of driver speeding - but now driving 80, 85, and 86+. Better to keep the speed lower and risk the ticket than open the gate for driver's who don't have the judgement, experience, etc. to speed in the first place.

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The speed at which a car could really injury a pedestrian is about 15 mph. I gather want the speed limit to be somewhere in that range.

joko104 said:

The speed at which a car could really injury a pedestrian is about 15 mph. I gather want the speed limit to be somewhere in that range.

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I'm not sure what you're trying to say here. Highways outlaw pedestrian traffic, so that isn't an issue there.

MoSurveyor said:

I'm not sure I understand your question. Do all traffic engineers shoot for this percentile? As a base, yes, but that is adjusted by the other variables mentioned like side road access, sidewalks/pedestrian traffic, etc., etc.

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Right. I'm honestly curious as to whether this percentile is taken to be fixed (which I'm guessing it is) or if they ever readjust it it.

Most traffic laws and safety practices in this country are universal - so what, exactly, do you mean?

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I'm talking about the responses to said law. I've been all over the country, and some places such as Arkansas have amazingly slow drivers. For others, such as many Atlantans, the speed limit is only a concept.