rant: should i have got this speeding ticket?

[Rothrandir]

nra, i wasn't using your situation as an example, i was just talking in general, as i've heard many similar sad stories.

i realize that a split second can indeed make all the difference, but most of the time it won't. maybe instead of dead you might end up slightly less dead. i don't know but for the most part, a little extra speed won't affect that much. there are certainly cases where it does and has, but there are also cases where going the limit would have resulted in the exact same thing.

for the most part, the kinetic energy equations are worthless, because while the damage induced by a collision may be greater (or rather, the force, not necessarily the overall damage), the whole point is that driving 10mph over the limit isn't likely to make you any more likely to actually get into a crash. lets face it, if you get into a decent crash at 65mph, you're probably screwed anyway.

again guys, i'm not advocating driving 100mph when there are people around you driving 70, that's irresponsable and stupid. i'm talking about when theres noone else on the road, or when everyone is driving a similar speed.

personally, i think that if theres a guy driving on an open road with noone on it, a cop should really have no reason to pull him over no matter what speed he's going. (naturally 120 or more would be pushing it in some areas!). still, i think that there are a lot of roads that can be safely sped up beyond what they currently are. and there are also roads which are accuratly marked, and i'm sure there are even roads out there that are probably marked a little too fast. i've said it once and twice and i don't know how many times, but it all depends on the conditions. i suppose this is one of the most difficult thigns to determine when deciding on a speed anyway, and it's difficult to get a good compromise between having a law or limit that allows too much individual interpretation and a law that is so strict as to not consider outside variables.

 

[357]

And for headons, if the speed limit is 100, and both cars are going 100 in opposite directions, that is approximately equal to a 200 mph collision. And as Turbodog mentions about the energy, a 200 mph collision would have most likely devastating energy.

 

[turbodog]

[ QUOTE ]
357 said:
And for headons, if the speed limit is 100, and both cars are going 100 in opposite directions, that is approximately equal to a 200 mph collision. And as Turbodog mentions about the energy, a 200 mph collision would have most likely devastating energy.

[/ QUOTE ]

Actually, no. With both objects at the same velocity AND mass, it would be like hitting a stationary object (tree/bridge/brick wall).

Good try! /ubbthreads/images/graemlins/tongue.gif

 

[gadget_lover]

[ QUOTE ]
Rothrandir said:

for the most part, the kinetic energy equations are worthless, because while the damage induced by a collision may be greater (or rather, the force, not necessarily the overall damage), the whole point is that driving 10mph over the limit isn't likely to make you any more likely to actually get into a crash. lets face it, if you get into a decent crash at 65mph, you're probably screwed anyway.


[/ QUOTE ]

Kinetic energy is what it's all about. Metal bends at different level of force If a 10 MPH increase doubles the stress, the metal that would have held up at 55 MPH may buckle at 65. The air bag that may save you at 65 may be useless as your car flips the 7th or 8th time.

And don't forget how many times you've missed an accident by only a foot or two thanks to fast reflexes. Take away another 2/10 of a second from the time available to react and it may well make all the difference.

[ QUOTE ]

again guys, i'm not advocating driving 100mph when there are people around you driving 70, that's irresponsable and stupid. i'm talking about when theres noone else on the road, or when everyone is driving a similar speed.

personally, i think that if theres a guy driving on an open road with noone on it, a cop should really have no reason to pull him over no matter what speed he's going.


[/ QUOTE ]

I used to have that opinion too. I asked a cop why I was being busted at 4 AM on a deserted street for 60 in a 35 zone. I was not endangering anyone. The streets were deserted. His reply? "Well, Son, I'm here, now aren't I?"

I got the point that I could not be sure that no one else would pull out of a drive way or side street.

Daniel

 

[357]

[ QUOTE ]
turbodog said:
[ QUOTE ]
357 said:
And for headons, if the speed limit is 100, and both cars are going 100 in opposite directions, that is approximately equal to a 200 mph collision. And as Turbodog mentions about the energy, a 200 mph collision would have most likely devastating energy.

[/ QUOTE ]

Actually, no. With both objects at the same velocity AND mass, it would be like hitting a stationary object (tree/bridge/brick wall).

Good try! /ubbthreads/images/graemlins/tongue.gif

[/ QUOTE ]

I'm not following....so is that worst or better for the driver?

(i.e. hitting a brick wall at equivalent of 200 mph)?

 

[jtr1962]

[ QUOTE ]
gadget_lover said:Cool! DO you remember the text or source of the 100MPH design criteria? I've not been able to find anything but assertions.


[/ QUOTE ]
I'm having trouble finding stuff online myself, but I remember distinctly reading this and hearing it when I was younger. As KC2IXE asserted:
[ QUOTE ]

That said - I believe you are right that the design speed for most was in the 80 mph range, although MANY were designed for a LOT more.


[/ QUOTE ]
My emphasis on "a lot more", especially if you're going by curvature radius. Some roads have curvature radii of 3000 meters or more nearly everywhere. This evidently means they were ultimately planned with very high speeds in mind once automotive technology caught up.

You might find this interesting. Here are some of the more interesting points of the article:

1. Uniform design standards called for design speeds of 70 MPH, lanes 12 feet wide, gradients not to exceed 6 percent and bridge clearances of fourteen feet. [5] As people who drove the system when it opened know, the speed limit, with very few clearly marked exceptions, was 70 MPH.

2. The report showed that lowering speed limits by as much as 20 MPH or raising speed limits as much as 15 MPH had little effect on driving speeds. They found that lowering speed limits below the 50th percentile did not reduce accidents but did increase driver violations. They found that raising posted speeds did not increase speeds materially or increase accidents.

3. Studies show that the 85th percentile is the safest speed limit. However, the 85th percentile is not a fixed speed. It may be that the comfort speed level increases with time and the 85th percentile increases accordingly.

My comments: The 70 mph design speed was based on automotive technology of 50 years ago, and it was considered to be the absolute minimum speed for which any Interstate highway should be designed. Most were designed with the "mythical" 100 mph speed in mind, or could easily be converted to such standards by realigning curves and lengthing on-ramps. Also note that #3 supports my assertion that as automotive technology improves the so-called 85th percentile actually increases. I remember in the late 1960s most drivers drove at Interstate speeds in the 65 to 80 mph range. Nowadays you'll see somewhere in the 80 to 90 mph range on many of the same roads. What happened is that cars have gotten more stable at higher speeds thanks to better engineering. If not for SUVs, I think 85th percentile speeds might be close to that magic 100 mph mark on many roads.

[ QUOTE ]
Lets see. that means the frontal area shrinks to about 4 foot high by 5 foot wide. Now that's a seriously small car. I'm not sure you will fit 4 adults comfortably into that. You could make it 6 foot wide and 3.3 feet high, but my back would not allow me to climb into it.

A Prius is reasonably slippery. It's got a CD of .26 The Honda Insight is .25. The Ferarri appears to be in the .3 range. The 2005 corvette is .28 I've never heard of a production car with a CD as low at .1 What shape does it take to get a cd of .09? Would that shape be drivable?


[/ QUOTE ]
Think of something like those bullet bikes but wider for a Cd of 0.09. You can have Cds way lower, but the vehicle wouldn't be driveable. Also, if we can get laminar flow (which increases with V instead of V²) instead of turbulent flow there will be an even larger drag reduction. To put things into perspective about how far we can go, we have made vehicles which can exceed 80 mph on human power alone. Many, including myself, think it is possible for one of these vehicles to break the century mark. If so, designing a 4 person car which gets 100 mpg at 100 mph would be a fairly simple exercise. And small, low vehicles can be made easy to get in and out of by simply having built-in jacks which lift them a foot or so off the ground when they're parked. 20 ft² is higher than you mentioned because the tires add about 9 inches to the height without much frontal area. The roof would probably be about 4 feet high for a car that's 6 feet wide, not the 3.3 feet you said, Your back will be fine, especially with the "lifts". /ubbthreads/images/graemlins/wink.gif It seems almost asinine to waste gas on a big, tall SUV mostly because it's easy to enter or exit. I won't even get started on what I think of the physical condition that most people in this country are in that entering a low vehicle should even be an issue unless you're over about 75. Putting aside this topic for a moment, I really would like to see more people walking and biking to their destinations instead of driving. Driving is one reason we have so many people in such bad shape at relatively young ages.

[ QUOTE ]

Can you actually drive a car safely at 100 MPH with the super stiff compounds in the ultra low rolling resistance (ULRR) tires? I have low rolling resistance (LRR) tires on my car and they are not the best in terms of handling and stopping.


[/ QUOTE ]
Why not? Remember what I said about banked curves? You can bank enough so that the forces are neutral at whatever speed you choose. Under those conditions, as far as the car is concerned, it's going in a straight line (just with a little more weight from the resultant of the cornering force and gravity). You can theoretically take such a curve on glare ice with no problems (not that I would try it). Believe me, the difference between ULLR and regular tires isn't that significant unless you drive right at the car's limits, and you shouldn't do that unless you're at a racetrack. As for stopping quickly, why not design cars with air brakes which supplement the wheel brakes? These would be surfaces which pop out so as to dramatically increase drag whenever emergency braking is applied, and they would be very effective at high speeds. Do you see a trend here? For every problem you can come up with there is an engineering solution. /ubbthreads/images/graemlins/wink.gif

[ QUOTE ]

Most of the accidents happen when a car changes lanes or while merging. I don't have the figures but recall it was a very high percentage. You are begging for accidents when you have incoming traffic 30 mph slower than traffic. In my experience, most cars don't even get up to 65 by the end of the on-ramp so the speed differential is even higher.


[/ QUOTE ]
Make the on ramps longer. Where you can't, lower the speed limit in that area. I agree 100%. Speed differential, not speed, causes accidents.

[ QUOTE ]

The accidents chronicled in the daily news tells me that the roads are not very safe at 65 MPH. They might be if, like railroads, the traffic was strictly controlled and following distances were enforced, but we are talking cars and streets and human drivers.


[/ QUOTE ]
Ultimately, I feel we should move to automated cars for many reasons, not just to increase speeds (although that alone would make it worthwhile). In the mean time, we can do a lot more to increase safety and speeds. I think racing car type harnesses and roll cages should be required equipment on all passenger vehicles.

[ QUOTE ]

Hmmmm Speed Nazi. You get dragged away when you speed? OK.


[/ QUOTE ]
Just a term I've heard. I don't like when people who know nothing about a subject start talking in absolutes, as in 80 mph is always unsafe, or 55 mph always is. The fact is that given enough money and incentive, you can design roads and cars to be safe at any speed within the limits of the technology (which I would put at roughly 150 mph for mass-produced vehicles today). We already have many roads which would be safe at 100 mph (or even more). Why not use them as such, even if it means we have to restrict which vehicles can use those roads (by all means exclude SUVs)? Remember that driving is a privilege, not a right, and the state can set whatever standards they wish for both motor vehicles and drivers. I would rather those standards be high enough to exclude marginal cars and drivers. That alone would make higher speeds and fewer accidents almost a given.

About the "radar" defense, I don't think it would hold. /ubbthreads/images/graemlins/grin.gif

 

[turbodog]

[ QUOTE ]
357 said:
[ QUOTE ]
turbodog said:
[ QUOTE ]
357 said:
And for headons, if the speed limit is 100, and both cars are going 100 in opposite directions, that is approximately equal to a 200 mph collision. And as Turbodog mentions about the energy, a 200 mph collision would have most likely devastating energy.

[/ QUOTE ]

Actually, no. With both objects at the same velocity AND mass, it would be like hitting a stationary object (tree/bridge/brick wall).

Good try! /ubbthreads/images/graemlins/tongue.gif

[/ QUOTE ]

I'm not following....so is that worst or better for the driver?

(i.e. hitting a brick wall at equivalent of 200 mph)?

[/ QUOTE ]

For each vehicle it would be like hitting a stationary object at 100 mph.

This is a classic physics problem for what it's worth.

 

[jtr1962]

[ QUOTE ]
turbodog said:
I have heard that most accidents occur at around 30-40 mph. I am sure someone can chime in on this one.


[/ QUOTE ]
Yes, and most of those accidents occur on local roads, not the limited access highways on which some people here (including myself) advocate raising speed limits. Despite advances in automotive safety technology, 30 to 40 mph is more than enough to kill you. All your talk of kinetic energy at 65 mph versus 100 mph is moot. If you hit a stationary object like a tree you're probably dead at 30 mph, definitely dead at any speed over 40 mph. In the small amount of space from where you run off the road until you hit the tree you won't be able to decelerate to under 30 mph whether you were going 65 mph or 100 mph, so the argument about having a little extra time to react is moot. It won't save you're life here. Yeah, you shouldn't be going so fast you fly off a curve into a tree, but I've been saying so all along. Curvature radius alone should dictate maximum speed on limited access highways.


Your arguments are more valid for local driving where factors other than the road profile dictate maximum safe speeds. This is why you should have left the higher speed examples out. Even here, we're usually talking speed differentials more than absolute speed. Let's take a few examples where two cars have an accident with a speed differential of 30 mph:

KE in parentheses

Car 1: 0 mph (0)
Car 2: 30 mph (900)
Difference: 900

Car 1: 20 mph (400)
Car 2: 50 mph (2500)
Difference: 2100

Car 1: 50 mph (2500)
Car 2: 80 mph (6400)
Difference: 3900

Car 1: 70 mph (4900)
Car 2: 100 mph (10000)
Difference: 5100

Note that we are assuming here that car 1 has an infinite mass, and continues at the same speed as before the collision. Car 2 loses enough kinetic energy to decelerate by 30 mph, and this is therefore the energy of the collision. This is obviously unrealistic because car 1 would speed up upon impact. However, I'm playing devil's advocate by choosing a worst case scenario. Even so, note that the collision with car 2 going 100 mph instead of 30 mph is only 5.67 times worse, rather than the 11.11 times worse which the kinetic energy differences between 30 mph and 100 mph would lead up to believe. I don't recall all the physics, but I think when two bodies collide with a certain speed differential and elasticity the energy dissipated in the collision is actually the same regardless of the absolute speeds of the objects. Only the relative speed matters.

My point here is that real-world collisions usually involve a speed diffential rather than crashing into a stationary object. All other things being equal, a 30 mph relative speed collision isn't any worse as speed increases, and since we're talking only speed differences, reaction times are the same. It makes no difference whether someone is doing 30 and you're doing 60, or if they're going 70 and you're going 100. Your relative speed is 30 mph, and that is what determines whether your reaction time is fast enough to avoid an accident. In fact, it's much easier to scrub off 30 mph of speed when you're going 100 mph than when you're going 50 mph. You have your brakes plus significant drag to slow you. And to make it more interesting, if you happen to see an out of control driver barreling towards you in your rear view mirror, and there's nobody in front of you, isn't speeding up the most sensible thing to do in order to minimize or even avoid the collision? The extra second you give the other driver might be all he needs to slow down enough to avoid you. Slower and or slowing down isn't always safer. I've avoided getting rear-ended once by an out of control van while cycling by speeding up to get out of his way. Other times slowing down was the most prudent course.

If you feel the need to drag physics into this then let's stick with f=v²/r, and f=ma. This is all that's relevant. When f exceeds the ability of the tires to hold the road because either v or a is too high or r is too low, then you come off the road or have a collision. Either you took a curve too fast or you didn't have enough room to stop before an obstacle. Unless you hit a brick wall all that matters as far as the severity of the collision is the speed differential and differences in mass. While those pictures of cars wrapped around trees at 100 mph may be sensationalist, the driver would be just as dead if they had hit the tree at the legal limit. The lesson is clear here-don't drive too fast for your vehicle, the road, and traffic. Attempts by the state to pick some arbitrary speed limit as "safe" are largely doomed to failure. Such attempts in the end simply lead to catering to the lowest common denominator. A perfectly straight road in good weather with no traffic has no inherent unsafe speed. Artifically low limits cause accidents by creating greater speed differentials. The least skilled driver who might otherwise avoid the road entirely might proceed at 5 or 10 mph under the legal limit while most traffic will be 15 or 20 mph over it. Set the limit 25 mph higher and that least skilled driver will avoid the road entirely. The remainder of the traffic will mostly fall nicely into a band from 10 mph under to maybe 5 mph over the speed limit. Voila, the maximum differential is reduced from a very dangerous 30 mph to a much safer 15 mph. The need to enforce limits is reduced to practically nil, so cops can concentrate solely on drunk, incompetent, inattentive, or aggressive drivers (yes, some speeders fall into this category).

 

[turbodog]

[ QUOTE ]
jtr1962 said:
[ QUOTE ]
turbodog said:
I have heard that most accidents occur at around 30-40 mph. I am sure someone can chime in on this one.


[/ QUOTE ]
Yes, and most of those accidents occur on local roads, not the limited access highways on which some people here (including myself) advocate raising speed limits. Despite advances in automotive safety technology, 30 to 40 mph is more than enough to kill you. All your talk of kinetic energy at 65 mph versus 100 mph is moot. If you hit a stationary object like a tree you're probably dead at 30 mph, definitely dead at any speed over 40 mph. In the small amount of space from where you run off the road until you hit the tree you won't be able to decelerate to under 30 mph whether you were going 65 mph or 100 mph, so the argument about having a little extra time to react is moot. It won't save you're life here. Yeah, you shouldn't be going so fast you fly off a curve into a tree, but I've been saying so all along. Curvature radius alone should dictate maximum speed on limited access highways.


Your arguments are more valid for local driving where factors other than the road profile dictate maximum safe speeds. This is why you should have left the higher speed examples out. Even here, we're usually talking speed differentials more than absolute speed. Let's take a few examples where two cars have an accident with a speed differential of 30 mph:

KE in parentheses

Car 1: 0 mph (0)
Car 2: 30 mph (900)
Difference: 900

Car 1: 20 mph (400)
Car 2: 50 mph (2500)
Difference: 2100

Car 1: 50 mph (2500)
Car 2: 80 mph (6400)
Difference: 3900

Car 1: 70 mph (4900)
Car 2: 100 mph (10000)
Difference: 5100

Note that we are assuming here that car 1 has an infinite mass, and continues at the same speed as before the collision. Car 2 loses enough kinetic energy to decelerate by 30 mph, and this is therefore the energy of the collision. This is obviously unrealistic because car 1 would speed up upon impact. However, I'm playing devil's advocate by choosing a worst case scenario. Even so, note that the collision with car 2 going 100 mph instead of 30 mph is only 5.67 times worse, rather than the 11.11 times worse which the kinetic energy differences between 30 mph and 100 mph would lead up to believe. I don't recall all the physics, but I think when two bodies collide with a certain speed differential and elasticity the energy dissipated in the collision is actually the same regardless of the absolute speeds of the objects. Only the relative speed matters.

My point here is that real-world collisions usually involve a speed diffential rather than crashing into a stationary object. All other things being equal, a 30 mph relative speed collision isn't any worse as speed increases, and since we're talking only speed differences, reaction times are the same. It makes no difference whether someone is doing 30 and you're doing 60, or if they're going 70 and you're going 100. Your relative speed is 30 mph, and that is what determines whether your reaction time is fast enough to avoid an accident. In fact, it's much easier to scrub off 30 mph of speed when you're going 100 mph than when you're going 50 mph. You have your brakes plus significant drag to slow you. And to make it more interesting, if you happen to see an out of control driver barreling towards you in your rear view mirror, and there's nobody in front of you, isn't speeding up the most sensible thing to do in order to minimize or even avoid the collision? The extra second you give the other driver might be all he needs to slow down enough to avoid you. Slower and or slowing down isn't always safer. I've avoided getting rear-ended once by an out of control van while cycling by speeding up to get out of his way. Other times slowing down was the most prudent course.

If you feel the need to drag physics into this then let's stick with f=v²/r, and f=ma. This is all that's relevant. When f exceeds the ability of the tires to hold the road because either v or a is too high or r is too low, then you come off the road or have a collision. Either you took a curve too fast or you didn't have enough room to stop before an obstacle. Unless you hit a brick wall all that matters as far as the severity of the collision is the speed differential and differences in mass. While those pictures of cars wrapped around trees at 100 mph may be sensationalist, the driver would be just as dead if they had hit the tree at the legal limit. The lesson is clear here-don't drive too fast for your vehicle, the road, and traffic. Attempts by the state to pick some arbitrary speed limit as "safe" are largely doomed to failure. Such attempts in the end simply lead to catering to the lowest common denominator. A perfectly straight road in good weather with no traffic has no inherent unsafe speed. Artifically low limits cause accidents by creating greater speed differentials. The least skilled driver who might otherwise avoid the road entirely might proceed at 5 or 10 mph under the legal limit while most traffic will be 15 or 20 mph over it. Set the limit 25 mph higher and that least skilled driver will avoid the road entirely. The remainder of the traffic will mostly fall nicely into a band from 10 mph under to maybe 5 mph over the speed limit. Voila, the maximum differential is reduced from a very dangerous 30 mph to a much safer 15 mph. The need to enforce limits is reduced to practically nil, so cops can concentrate solely on drunk, incompetent, inattentive, or aggressive drivers (yes, some speeders fall into this category).

[/ QUOTE ]

Wrong analysis. You're assuming a rear-end collision between two moving cars. This is rarely the case at speeds above 10(?) mph or so. Highway accidents usually involve a collision with a stationary object (tree/bridge).

Also, it has been demonstrated years ago that a full frontal collision can routinely be walked away from by simply wearing seat belts at speeds over 30 mph. I'm not sure where this limit ends, but it clearly doesn't mean sudden death.

 

[jtr1962]

[ QUOTE ]
turbodog said:
Wrong analysis. You're assuming a rear-end collision between two moving cars. This is rarely the case at speeds above 10(?) mph or so. Highway accidents usually involve a collision with a stationary object (tree/bridge).


[/ QUOTE ]
If so, then your points about kinetic energy at highway speeds are even more irrelevant. Hit a bridge abutment at the legal limit of 65 mph or at 100 mph, and the only difference will be how many pieces your body will be in. I'll believe your assertion that a 30 mph collision into such an object might be surviveable, but past about 40 mph we're splitting hairs. You're dead. While the g-forces involved decelerating from whatever speed to zero in the crush space of your car's hood might be technically surviveable at even 100 mph, the restraints and the car's body will give out long before you've come to a stop. After that, you squish against the obstacle like an insect. Remember the debate about bike helmets? Past a certain (very low) speed, you might as well be wearing a paper bag. Ditto for car restraints except the effective speed is much higher. They'll certainly help in the vast majority of car-car collisions, but hit a large truck or a stationary wall at any speed above perhaps 40 mph and you might as well be dancing on the seat. This isn't to negate the value of safety devices (including bike helmets), just to point out that they're not effective in some collisions even at "legal" speeds. Therefore, unless you're prepared to lower the limit everywhere to 30 mph, or better yet 15 mph (because of head-ons), you can't guarantee that all collisions will be surviveable. And if you do so, such a limit will be well-nigh impossible to enforce without governers. And as for bike helmets, unless you're prepared to ride under 10 mph and avoid colliding with cars all the time, they won't guarantee surviveability. Should we go around ticketing cyclists who go above 10 mph as well? Just food for thought.

Just because we may not be able to protect ourselves all the time if something goes wrong doesn't mean that we should restrict or limit certain activities. Plane accidents are rarely surviveable. Should we not fly any more? By the same token, why set speed limits artificially low, especially when those low limits give the illusion of safety only without the fact? If that's the case, we might as well take my earlier suggestion (a few posts back) and just set 5 mph speed limits. I can guarantee nobody will ever die in a car accident again, mostly because nobody will want to drive when they can walk just as fast.

I found another very interesting article. Here is the part I consider most relevant to the discussion:

Looking at the California data from an engineering and safety perspective, the flow at many times of the day is in the mid 80's and at times into the low 90's; therefore the 100 mph speeds would still be in the safest range on these urban interstates and there would not be an increase in accidents, speeds may be higher, but it supports Cirillo's risk curve finding. MDT reported a limited amount of vehicles at these speeds. California reports thousands per hour with reduced accident rates. People in many areas simply drive faster than Montanans, but if they're doing so safely there is nothing to fear, as demonstrated in Montana.

 

[turbodog]

[ QUOTE ]
jtr1962 said:
As for stopping quickly, why not design cars with air brakes which supplement the wheel brakes? These would be surfaces which pop out so as to dramatically increase drag whenever emergency braking is applied, and they would be very effective at high speeds. Do you see a trend here? For every problem you can come up with there is an engineering solution. /ubbthreads/images/graemlins/wink.gif


[/ QUOTE ]

Problem is, the engineering solutions are missing the financial ones to make it all work.

 

[gadget_lover]

I thought that problem was that the engineering solutions are not always compatible. For instance...

.09 CD shape with air brakes; The hinges create drag. The air brakes are not consistant (no effect with sufficient tail wind, for instance).

car bodies that raise to allow you to enter in ultra light low drag car; Adds to height and weight

Super low drag body with ultra LRR tires; Cross winds will push you off the road.

Ultra LRR tires at high speed are hard as rock. You need active dampening to smooth out the ride.

Creating laminar air flow for decreased drag; Adds complexity, cost and size. Even the military has not taken this technology into the mainstream.


On the subject of collisions. The assertion was made that it's only the speed differential that makes a difference in a crash. Please think back to the last freeway speed crash that you saw. Car A hits car B. B moves at a new angle (often just spins out of control) and hits either another car or a stationary object,. Car A may or may not follow Car B.

It would be nice if we really did have controlled access super highways. Unfortnately, you will always have cars that have to pull over and then merge again. You'll have the occasional animal that scrifices itself. You have the Police that pull over turn around and all sorts of things. It's not like a railroad where they can be fairly sure of what trains are ahead.

The best answer in MY book is to set the speed limits based on what's safe given average driving skills and current safety equipment. If a 55 MPH is survivable but 60 is not, then 55 should be the rule. That would suggest that we remove people with substandard skills and substandard cars, but that's a different discussion.

Daniel

 

[jtr1962]

gadget_lover,

Yes, engineering is always about the kind of compromises you mentioned. By optimizing A you degrade B and so forth. It's up to the engineer to find the best solution overall. Some of the things you mentioned aren't as bad in reality as you make them out to be. ULLRs are a little less sticky than regular tires, but new rubber compounds can change that. And I might point out that the lack of stickiness is more due to the need for long tire life than for low rolling resistance. Look at bike tires. They would classifiy as ULLR based on the rolling coefficient of 0.0025to 0.0035 (I actually confirmed this) yet they are very sticky. I've taken corners at 1g+ (i.e. right turns @ 25 mph). The thing is they only last about 4000 miles. You might need to compromise with tire life a bit for my hypothetical car. Maybe instead of lasting 80,000 miles the tires would last half that. The fuel savings would make up for it. Active dampening? No need-ride quality is based on the ratio of unsprung mass to sprung mass. Make the tires and rims lighter and you have a better ride. Lifts add weight? Perhaps 50 pounds. Weight isn't as big a factor in fuel economy as you think it is. You add a little tire drag, no more. A highly economical vehicle will have regenerative braking (Google for it if you don't know what it is) anyway, so the extra mass needed to acceleration will be rendered practically moot. Laminar flow? It's simply a matter of body shape. We haven't been able to reliably obtain it, but in time we will do so. In the meantime we can do a lot better as far as reducing Cd. Air brakes may add a little drag, but not much if done properly. Planes have all kinds of slats and movable control surfaces which add little drag. The idea is so sensible I think in time they'll be standard equipment. My point is that we can do much, much better than we're doing now. I'm annoyed that we're hardly trying. SUVs are just about the worst possible thing for fuel economy. Even cars like the Prius could be made better. I don't consider 60 mpg anything to brag about. The biggest, worst cars on the road should be getting that now. Most should get well over 100 mpg. Fuel is a non-renewable resource. Pollution alone should be enough of a reason to reduce emissions even if it weren't.

[ QUOTE ]

On the subject of collisions. The assertion was made that it's only the speed differential that makes a difference in a crash. Please think back to the last freeway speed crash that you saw. Car A hits car B. B moves at a new angle (often just spins out of control) and hits either another car or a stationary object,. Car A may or may not follow Car B.


[/ QUOTE ]
True, but highways are designed so that cars don't ram into stationary objects head on at full speed. There's a reason you see those tanks of sand or water in front of objects. The idea is to slow the car enough so that people don't get killed. You may glance a guardrail in an accident, but that's seldom fatal. The big worry is flying over the median into opposing traffic. Higher medians are called for. They would eliminate obnoxious "rubbernecking" as a side benefit.

[ QUOTE ]

The best answer in MY book is to set the speed limits based on what's safe given average driving skills and current safety equipment. If a 55 MPH is survivable but 60 is not, then 55 should be the rule. That would suggest that we remove people with substandard skills and substandard cars, but that's a different discussion.


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If you're talking about guaranteeing survieability in all crashes based on current state of the art, then we need to set speed limits to 30 mph where there's no danger of head-on collisions, and 15 mph where there is. Sorry, but anything approaching a reasonable speed will not be surviveable all the time. You might want to read the second article I linked to in my last post. It's very long but basically says what I've been saying. The people who wrote it are experts on the subject. Some of the more important points in my words:

1) Raising or lowering speed limits has little effect on the actual speeds people drive at.

2) Traffic finds its own speed based on the road and traffic conditions.

3) Speed limits should be set at the 85th percentile, rounded up to the nearest 5 mph, on urban roads. On limited access highways, speed limits should be set at the 90th or 95th percentile, rounded up to the nearest 5 mph.

4) The safest drivers statistically are those who drive at the mean speed (currently 75 mph) plus 12 mph. This is currently 87 mph for average Interstate traffic. Drivers who go 100 mph are statistically as safe as those who go 65 mph. The most accidents are caused by those who go 65 mph or less, and to a lesser extent by those traveling 110 mph and more.

5) Current speed limits are often set at the 10th percentile or even less, making 90% of drivers law breakers. The result is that the statistically safest drivers mentioned in #4 receive the most tickets.

6) Due to improvements in automotive technology, the 85th percentile speed has been increasing at around 0.5 mph per year since the 1920s. This means speed limits should be reviewed regularly, and raised where appropriate.

7) Statistically, we're driving faster than ever yet the accident rate on limited access highways is lower than ever. In fact, except at merges accidents on freeways are rare events, and often involve single vehicles where the driver might simply fall asleep at the wheel.

8) Enforcement of arbitrarily low speed limits actually costs lives for a variety of reasons.

9) Speed limits in general do not result in improvements in safety. They exist simply because some sheriffs abused the meaning of "reasonable and prudent" in the 1930s and 1940s, and the courts needed a more accurate barometer for enforcement. They've since been turned into a revenue stream for localities. Hence the inertia to change them back to something reasonable.

There's much more in the article, but this and similar articles, along with my education on the subject, tell me that those supporting current policies are dead wrong. Literally. The public may complain about "speeders", resulting in capricious enforcement, yet it's that same public who speeds. If the public really felt that 65 mph was a safe and comfortable speed, then they wouldn't be driving much faster. They're saying one thing and doing another. Face it, the public is schizophrenic and frankly unqualified to call for enforcement in an area where they have little understanding. The police shouldn't enforce an unjust law because of public outcry. Rather, the public and especially politicians need to be educated on traffic engineering practices which have worked well for the last 50 years when applied properly. It is intentional ignorance of the subject which has led to the current situation. The politicians and the public may cringe at the idea of 90 to 100 mph speed limits on Interstates, but based on sound traffic engineering practices this is exactly what is called for. Even local roads such as the one where the author of this thread received his ticket may have speed limits set too low. I don't know because I haven't seen the road in question but I tend to think the 85th percentile speed on such a road might be 55 or 60 mph. In that case, he was going 1 to 6 mph under a proper speed limit. By law he may have deserved the ticket, but based on sound engineering practices he likely didn't.

 

[gadget_lover]

I can't refute the study you quote, but I have a hard timer believing it's valid. I base that belief on 30 years of driving. That includes a year of commuting over 5 hours a day. It also includes monthly trips of many hundreds of miles.

My observation has been that most of the traffic travels near the speed limit, even on long, straight rural areas. I travel with my cruise control set at the speed limit and I pass almost as many cars and trucks as pass me. Most cars do speed up and slow down a bit due to the faulty brain-foor-gas_pedal feedback loop. My mom, for instance will drop to 60 and speed up to 70.

I almost never get passed by a car doing 80 or 90. In a 5 hour trip I usually see two or three pods traveling at high speed, and one or two jerks weaving through the slower cars, racing to their accident. A couple of times an hour I see someone coming up behind me real fast.

It's interesting that some folks around here were still driving at 55 MPH two years after the speed limit changed to 65. I wonder where that phenomenon fit into the study when they concluded that changes of posted speed limit made no difference.

What you failed to say about that study is that the DEATH rate goes up in the crashes that happen at higher speeds. That's was found by the US dept of transportation.

I can only conclude that the quoted study did not take place in my part of the country. I will not speculate on whether it was scientifically valid.

Daniel

 

[jtr1962]

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gadget_lover said:
It's interesting that some folks around here were still driving at 55 MPH two years after the speed limit changed to 65. I wonder where that phenomenon fit into the study when they concluded that changes of posted speed limit made no difference.


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The whole 55 mph limit was an anomaly, so whether what you say is true or not is immaterial. In many cases drivers were literally forced to drive at 55 mph by police cruisers blocking all the lanes setting the pace. This is hardly an example of a freely flowing traffic condition. The fact the some people didn't speed up for a few years afterwards has more to do with the overzealous enforcement which literally scared them into driving slower than with any perceptions on their part that 55 mph was "safer". And I might add that despite the government wholehearted pursuing a campaign to brainwash the public that "speed kills" (remember the "Drive 55, Stay Alive"), they failed miserably. People, including many here, may still talk the talk, but they don't walk the walk.

[ QUOTE ]

What you failed to say about that study is that the DEATH rate goes up in the crashes that happen at higher speeds. That's was found by the US dept of transportation.


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Immaterial. Artificially low speed limits actually result in more crashes, both from enforcement and from those who block lanes playing "traffic cop". On average fewer people die per mile traveled with higher speed limits. That is all which is relevant here, not the severity of the crashes or how many die per crash (a ridiculous statistic, BTW). You're making a straw man argument. Most airplane crashes are uniformly fatal but the probability of dying in one is very low so we accept that, get on with our lives, and fly when we need to. Ditto for high-speed crashes which are exceedingly rare. If you think that better devices to enable greater surviveability in high-speed crashes should be made mandatory, then I'm in 100% agreement with you. If you think we should get marginal vehicles like SUVs off the road because they handle poorly and can't avoid accidents easily, then I'm even more in agreement with you. That is really the only way to reduce deaths, which is a common goal we both have here. As I said, speed limits have little or no effect on safety, although the perception may be different. The sensationalist news loves to cover these high speed crashes. They should be equally zealous when people die because a cop was hell bent on pulling someone over who was doing nothing more than going 78 in a 65 zone. If you want to get rid of all deaths from auto accidents then govern cars to 15 mph, or automate them. Nothing else will work. Letting traffic find its own speed is what results in the fewest deaths on average. Improvements in roads and cars are what ultimately brings lower death rates. Lower speeds don't. 50+ years of studies prove this. Speed limits have been reduced to a revenue function, pure and simple. Death rates actually go up when people who disregard speed limits because they're set too low disregard other traffic laws. If you want to make more business for trauma surgeons then by all means lower speed limits some more, or enforce them more zealously. If you want to bring some respect back for traffic laws set the limits as I recommended earlier based on sound traffic engineering practices.

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I can only conclude that the quoted study did not take place in my part of the country. I will not speculate on whether it was scientifically valid.


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I hardly ride in cars, yet I've noticed that highway traffic is moving faster than I ever remember. Remember that you're seeing a very small sample when you're traveling along the highway as opposed to observing in one spot. You only will see a few cars faster or slower than you simply because the others are not on the same road long enough to overtake you or be overtaken by you. This contributes to the erroneous perception that most people are driving the same speed as you are. Yes, most of the people who remain around you are driving at the same speed as you by definition. This doesn't mean they constitute the majority. Stop someplace with a radar gun for a few hours and you'll see what I'm talking about. I routinely see people going 70, 80, even occasionally 100 mph on local highways which are posted at 50. The majority, except for those who weave around to keep up their speed, are doing nothing unsafe even though what they are doing is technically illegal. I would rather the cops bust the people talking on their cell phones or putting on their make up at 50 mph who are oblivious to those around them. They are the ones who cause the most accidents, even if they're not always directly involved in them.

 

[gadget_lover]

I have sat with a cop and watched the radar. I had verbally assulted him after getting a ticket for driving what I thought was an average speed. He offered to let me see for myself. Very few (less than 1 out of 20) were more than a few MPH from the proper speed (low and high). I only watched for 15 or 20 minutes, but I was convinced.

By definition, If I cruise at exactly 65 MPH (verified by GPS, Spedo and Milage markers) and I can see 30 cars and only two pass me in a 10 minute period, I'm driving pretty close to average. Unfortunately, watching cars while stopped is almost impossible to judge without a radar gun or other measurement. Cops pace you to get your speed for an obvious reason.

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That is all which is relevant here, not the severity of the crashes or how many die per crash (a ridiculous statistic, BTW)


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Ok, I think we jumped the shark here. When common sense and government studies of fatality rates are deemed "irrelevant" then it's time to move on.

Drive safe,

Daniel

 

[jtr1962]

[ QUOTE ]
gadget_lover said:
I have sat with a cop and watched the radar. I had verbally assulted him after getting a ticket for driving what I thought was an average speed. He offered to let me see for myself. Very few (less than 1 out of 20) were more than a few MPH from the proper speed (low and high). I only watched for 15 or 20 minutes, but I was convinced.


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Do you not think that the cop's presence there didn't have a slight effect on the speed people were driving at? I've seen cars flowing along sudden reduce speed by 20 mph, and then a quarter of a mile away you see a stopped patrol car. Maybe on the road you're referring to the limit is set at the 85th percentile. Or maybe the cop's presence resulted in "compliance". I don't know, I wasn't there. Numerous studies say just the opposite, and it's well known that in order to accurately monitor speeds the monitoring device must be unobtrusive. Even an unmarked car on the side of the road will affect speeds, if for no other reason than people will slow in case the person merges back into traffic, or simply so they can see what's going on (i.e. rubbernecking).

My point here is that layman and politicians really have no business setting traffic rules or enforcement policies. Traffic engineers alone should set speed limits and other aspects of road design. If the limit they pick makes the local politician cringe, or the sheriff complain that revenue will fall, tough. It should be the law of the land where the traffic engineer's word is final, and the speed measurements are unbiased by those with an agenda. I remember reading about some politician insisting on using an 85th percentile measurement obtained during a snow storm to set the 25 mph limit that they felt was proper.

[ QUOTE ]

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That is all which is relevant here, not the severity of the crashes or how many die per crash (a ridiculous statistic, BTW)


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Ok, I think we jumped the shark here. When common sense and government studies of fatality rates are deemed "irrelevant" then it's time to move on.


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Let me apologize for being a little harsh in that response. Maybe it was uncalled for. I'm just getting a little annoyed that the sole justification left in most of the arguments here (not just yours) boils down to lower speeds result in a lower fatality rates. Sure they do, but that doesn't automatically translate to fewer deaths. I was merely trying to get the point across that if you raise the speed limit and have 2 (1 fatal) accidents instead of 5 (2 fatal) accidents, then yes, your fatality rate went from 40% to 50%, but since you had fewer accidents you had fewer people killed (1 instead of 2 in this example). That's why I said this statistic is meaningless. All it tells me is that more people die in each accident, but if accidents decrease that can more than make up for it. Germany' autobahn with no speed limits in places has a lower fatality rate per mile traveled than US highways with speed limits. I won't argue that a greater percentage don't die in autobahn accidents due to the higher speed, but then again far fewer accidents happen to begin with so overall fewer people die per mile traveled.

And as I said, there is no reasonable speed where you can guarantee that no accidents will be fatal, which is what it seems that you are trying to suggest here. If you lower the limit to 55 mph, fewer accidents will be fatal, but there will be far more of them, some due to enforcement. You also end up with a mushroom effect of people avoiding the slow highways and taking more dangerous local routes because they make better time (and avoid tickets), and you have yet more people killed. It honestly wouldn't bother me if 100% of accidents were fatal due to higher speeds if we only had 100 of them per year. That would mean 100 deaths instead of the current 50,000. And I feel the need to point out that the majority of fatal accidents don't even occur on limited access highways anyway. They occur on country roads, mostly at intersections or driveways.

Sorry if any of this seems counterintuitive, but then again that's another point. Once we set laws based on emotion or ad hoc "observations" instead of findings of fact then we're treading on very dangerous ground. We end up with laws which make a harmless action illegal on the theory that they may be preventing a harmful outcome. NYC's sidewalk cycling law is one example of this. Arbitrarily low speed limits set well below the 85th percentile and/or the design speed of the road are another.

 

[Draco_Americanus]

Very interesting thread!
It's been my limited experance and close calls on the highway where the people that have nearly caused a crash have been
A. People going too slow
B. People trying to avoid or pass the people going to slow
C. Slow animals trying to cross the highway
D. People trying to miss slow animals
I personaly had option C happen to Me 3 weeks ago.
I wonder what the engery transfer was. Rusty 1988 S-10 traveling at aproxmently 60mph (I had seen the deer and slamed the brakes) hiting a male deer along his shoulder with his head at the vehicals center. The deer was killed on impact and sent across the 3 lane highway(I was on an on ramp) coming to rest near the center divider. It's antler punctured My radiator and then broke off, the front drivers side was crushed to the front wheel, the radiator also hit and bent the fan. I felt realy bad over the whole ordeal then got side tracked while wondering how mutch energy was transfered to the animal and viseversa. anyone know how to figure that out ? I hate to be morbid but this is a chance to learn something as well.

 

[jtr1962]

The collision between your car and the deer is an inelastic collsion, meaning that momentum is conserved but kinetic energy isn't. Assume that your S-10 weighs 4000 pounds and Bambi weighed 300 pounds. Furthermore, you said you were traveling 60 mph at the time of the collision. Let's assume Bambi was stopped, or moving very slowly. By conservation of momentum, you both ended up at a speed of 55.8 mph after the collision with Bambi embedded in your truck. The total change in kinetic energy was 45858 joules. This is the energy which went into bending the sheet metal of your truck and killing Bambi. To get an idea of this energy in terms of other things, a fully charged 2100 mAH AA NiMH cell stores roughly 9070 joules, so the collision was equivalent to discharging 5 AA cells in a fraction of a second. Or put another way, you could light an LIII for about 5 hours on the energy dissipated in this collision, or you could heat from room temperature and boil about 18 grams of water (about 5/8 of an ounce) of water. Not a lot of energy, but since it was dissipated in less than a hundreth of a second the effect was devastating. I've heard that it takes less than 100 joules to kill a human being if properly delivered. In the right weapon, a AA NiMH might be good for close to 90 "kills".