Nationwide 55 MPH Speed Limit

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Why is this not a topic of discussion nationally considering how much we would save in terms of fuel and lives?

:think:

of the 55 mph limit. With the current and future situation concerning oil and it's availablity and price it's madness not to do everything you can to reduce comsumption and dependence on finite resources.

Afterall, American egos want it all.

Across much of the country 55 was a joke. Nobody obeyed it and nobody would bother to enforce it. Even in my old home state of Connecticut. State Police Radar guns were set to 72MPH regardless of the speedlimit being 45, 55 or 65 on the highway.


Besides if you really wanted to save fuel the speed requirement should be 37 +/- 2MPH. No faster nor slower.

The total number dropped. But speed limits on secondary roads were dropped to 50MPH at the same time, where they still remain. Most fatalities don't occur on the limited access highways, but instead on two lane roads. Also seatbelts were mandated in the 60's and shoulder harnesses were incorporated in the early 70's along with padded dashboards etc. Makes it very difficult to conclude from a single stat about total number of deaths being related solely to speed reduction on only one type of road (Limited access highway).

which probably reduced accidents as well.
Drivers would watch for speed traps.
If the fast lane was empty, it meant there was a speed trap ahead;
everyone would drive past the cop at 65+ but in the slow lanes.
When drivers going one direction past a speed trap for the other direction,
they would turn their headlights on to warn drivers going the other direction.
If the roads were clear, people would look carefully at the sides of the road far ahead,
to see if there was someplace a police car could be hiding.

My car shifts into 4th and the torque converter locks up at 38 MPH. Cars differ on what speed is the most efficient. Vehicles with a flat torque curve can go faster, i.e., up to 60/65 for optimum gas mileage.
It depends on the engine, tire size and final gear ratio. Blanket statement don't come close to covering it.
Around town I need to be doing 40 at least for best gas mileage.

Also on trips to a town 200 miles away, @ 55 MPH I arrived tired and not that alert. Doesn't happen when I go the speed limit of 75. Traffic accidents went up from shear boredom.
Coming back recently, I made 34 MPG, for a round trip of better than 31 MPG. Yeah, at 76¾ MPH both ways.
This was in a 2004 Cavalier.

doesn't mean that if the optimization was reset your car would not do conciderably better at 37MPH.

The faster you go the more energy and power you waste in heating up the air around the car thru friction. Traveling at 74MPH dissipates four times the power in air friction/heat that going 37MPH does. Alternatively if you travel too slowely the incidental energy consumption of running things like air conditioning, lights, etc takes away too much from the overall efficiency and costs you more total fuel over the trip than the losses due to friction from going faster.

Easy enough to test to find the truth for yourself. I did when my car was newer, it had 20,000 miles on the odometer. Best fuel economy was between 70 and 75 MPH in 5th gear.

Now the car has 200,000 miles. Don't know if that speed is still MPG optimal, or not.

In 4th gear and all lower gears as well, each single revolution of the crankshaft pushes the car forward fewer feet.

I didn't write the laws of Physics, just have to work within them.

Force due to airodynamic friction on a solid body is proportional to V^2

With a doubling of speed the drag (force) quadruples. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power.

So, a car at 100mph needs 8 times more horsepower to cut through the air than one at 50mph. At 75mph, the car needs 2.5 times more horsepower to overcome air resistance than it does at 55mph.

Getting away from all the theory, MPG tests with a particular, operating vehicle is conclusive, though it may or may not be representative for all similar cars of the same model. Multiple tests undoubtedly give greater confidence in the data derived.

Going toward theorey, even if higher horsepower is required to go faster, the fact that a top gear causes the car to move a greater distance with each single revolution of the engine, may (and does with our car) offset the required HP increase to overcome whatever resistances require more horsepower such as rotating weight speeds, rolling resistances, and other factors including wind. Our particular car was advertised as one of the lowest wind resistance figures at the time it was built (1986), the point being that your mileage may vary by make and model. Simply by actually testing a vehicle, one finds the truth for the car tested, regardless of what theory may or may not say, or even should say.

HP is probably not as important as torque anyway, and there are multiple ways, or so I've read, of interpreting what HP actually is.

Sometimes theory will tie one's brain up in knots. Running a test, or series of tests (such as at different speed and load conditions) on an existing vehicle is much simpler, though I agree it doesn't shed insight upon engineering changes that if made might result in greater efficiencies. If a smaller engine was put in a particular vehicle, then the series of tests would need to be rerun for confirmation of any ideas explored by the engine change. However, with smog laws as they are, it's all 'academic' anyway, as changing a particular vehicle's engine to a smaller one is made difficult by regulatory smog-law hurdles.

Looking back at your prior post, sure, if one alters the vehicle with gearing and engine changes, different from those the factory engineers selected, then there may be more optimal ways to gain better efficiencies at any given speed. I believe this is being done now by some car companies, certainly smaller companies, and is continuing to be explored in the search for greater fuel efficiencies.

However, if speed limits are changed to slower speeds such as 55MPH, and a portion of the populace are still driving vehicles that get better MPG figures at higher speeds than lower, instead of newer vehicles designed with better efficiencies for slower speeds, then that portion of the populace will see an increase in the consumption of fuel to get where they are going. This may be considerable in a poor economy where massive numbers of folks cannot afford the latest and greatest technology. They'll just keep driving their old vehicles until they can no longer afford to drive, then they're stuck where they are, given the lack of public transportation in many areas including some big cities.

A regular gasoline engine vehicle is most efficient at peak torque RPM with the throttle wide open in top gear. You never see these conditions continuously except when accelerating, possibly to illegal speeds, or driving up a gradient: The point is that running at too low RPM at too light a load doesn't yield optimal efficiency, even if the MPG is slightly higher. For instance:

My car yields 30 MPG when I average 80 MPH on long trips and 35 MPG at 50 MPH. The higher speed results in much greater load on the engine as you have correctly stated, but this increase in load results in an increase in efficiency for my car. Since my time is worth money, why wouldn't I cruise at more than 50 MPH? Less than that, and I can't use top gear.

A tall wide blunt SUV may show a much larger MPG penalty for speed, but then its engine would already be working much harder at low speed.

That is one of the advantages of a manual transmission, if the road is flat, you can shift it into its highest gear at very low speeds. Automatics must be set to go to a higher gear at certain speed (or more accurately rpm speeds). A manual you can leave buck for little while when things are marginal, while an Automatic will keep on shifting up and down in such marginal situation and get worse fuel economy (Thus Automatics must operate at higher speeds then Manuals for optimum fuel economy). This ability to operate efficiently at speed substantially below 50 mph is one of the reasons manual transmission get better fuel economy then an automatic if both are being operated for maximun fuel efficieny.

A further factor is that cars made for the US market can only use EPA fuel economy numbers. EPA tests are done at 50 mph, and thus makers of Cars for the US market design their cars to be at they best at 50 mph, even if that means WORSE fuel economy at lower or higher speeds. Given modern electronics, which control most engines and transmissions, this is NOT that hard to do. Today even the automatics transmission is controled by electronics, thus the engoine/transmission can be set to give its best milage at whatever speed the car maker wants it to be (and that is 50 mph to max the milage figure on the EPA tests). The second EPA test, the "City Test" is a series of stop and accleration between 0 mph and 50 mph (nothing higher) which is also taken into consideration by automabole sellers. For all these reasons, the best fuel economy for automatics tend to be at speeds no higher then 50 mphs (For cars marketed for the US Market). Manual Transmission can do better at lower speeds, but that is do to the fact that with a Manual Transmission a driver can keep the car closer to the speed where the engine/transmission will start to buck. For this reason, in most EPA tests, geared for 50 mph, Manual trasnmissions are just marginally better then automatics. This is also true for cars like the VW Lupo, which was design to operate most efficicely at 35 mph, not 50 mph (and for that reason NOT sold in the US, even through the Lupo had even better fuel economy than the Toyata Prius).

As to Traffic Accidents, when 55 first became the law, accidents went down and stayed down till the price of Gasoline started to drop in the early 1980s. With cheaper gas, speed and accidents went up. One of the reason for the drop in accidents in the 1970s was that even rural dirt roads had speed limits up to and above 70 mph. The 55 mph speed limits forced states to lower these speed limits AND MOST STATES DID NOT RAISE THEM WHEN THE FEDERAL SPEED LIMIT WAS REPEALED (in fact most states only raised the speed limits on limited excess or other modern design four lane highway). This reduction of speed on such secondary roads reduced accidents (most rural roads have higher accidents rates on a per mile driven on that road basis then almost all Interstates, even urban interstates, do to excessive speeds on roads design for horse and buggy speeds). If you restrict your view of accidents on the roads most states permitted to go over 55 (Interstates only) these are some of the safest roads ever designed dn the Accident rate went up just marginally, if you include the non-limited access highways where the max speed is over 55, the rates are up tremously (Few states have done this and then only in certain areas).

The best example of this is Montana and its decision to go to unlimited speed limits when 55 was abolished. This caused so many accidents for the interstate highway system was only designed for 70 mph traffic (Just like the country roads, speeds in excess of the design of the highway) that Montana had to first reduce the max speed at night to 70, and then to set the max speed at 70 even for daylight hours, to many people were getting killed when traveling at speeds in excess of the design of the Highway.

Except for the Interstate Highway system (and some other limited excess highways) most roads were design for speeds no greater then 50 mph and accidents increase immensely when speeds are done in excess of the design of the highway.

NOBODY obeyed it back then. I'm guilty too. If we had it again, it might be different this time.

If only we had listened to Jimmy Carter back then....but we didn't. As punishment we ended up with Saint Reagan. Grrrr.

Back in the 70s, the last time we tried it, the local Boss Hogg types sent out their armies of road pirates (aka traffic cops) to entrap people used to driving somewhere closer to the speed that the roads and vehicles were designed to accommodate.

That having been said, I would get behind a national speed limit if a local government's maximum speeding ticket revenue was fixed at some percentage of their annual budget, with any excess fines collected going irrevocably to alternative fuels research. This would take the profit motive away and limit the opportunities for financially-motivated police abuse.

Of course, we could also tell the gluttons in Detroit and Houston to go fuck themselves and raise CAFE standards. That would accomplish the same thing, without giving Boss Hogg and Roscoe P. Coltrane a big fishhook with which to pick the pockets of the public.

shipping would take longer (and therefore be more expensive). Many of the midwest/western (i.e. non populous) states have speed limits in the 65-75 range (I think even Texas might have one that's 80MPH). Dropping it to 55 would impact their bottom line, which obviously they would just pass on to consumers.

It boosts me another 3 mile per gallon over a 50 mile one-way trip to work.

I don't care if individuals want to drive 55 on the highway as long as they stay out of my way.

then I pass them and get back into the right lane ahead of them.

Not so much. And like last time, it's largely unenforceable.

If you want people to save fuel, then tax the hell out of gas (like they do in Europe). $7 or $8 a gallon gas will change driving habits and hasten the death of the land barges a LOT faster than reinstating the double nickel.

But car ownership in Europe continues to climb, and anyone who has driven there cna attest that there is hardly a noticeable practice of gentle acceleration and moderate speeds.

I'm a pretty aggressive driver. I can handle Chicago off peak packed high speed highways and NYC jammed crawls and Boston parking nightmares and Montana effective lack of speed limits just fine, but Palermo reduced me to a gibbering heap, as it's a combination of all of them in a city made for horse carts.

I only kid myself into thinking I am a competent driver - then I go to Europe. I still remember my first rush hour (every hour as far as I can tell) cab ride from Victoria station to St John's Wood. Shaved about 10 years off my life - particularly the roundabout at Hyde Park corner. I swore I would never drive inside the city then (thereby saving congestion charges too!)

May as well make everybody's trips so much longer.

So the folks that want to drive a hundred in cars that are designed specifically for that can do it. Meanwhile enforcing the speed limit in what would eventually become secondary highways would be much easier.
Driving on less crowded freeways would be more pleasant and enjoyable. People would be employed in another great WPA program. Fuel taxes could fund this whole project while helping us become less dependant on oil.

And all my early driving was under Carter's 55mph law. I thought it was a good idea with a positive impact, and I was sorry to see it go.

Proposal: You can drive 80 MPH if your car can average 30 MPG at that speed. If a car averages 30 MPG at 55 MPH, then that is your limit. If your car cannot average 30 MPG at your chosen average speed you have to pay a fine for every mile you drive. The fine would be based on the difference between 30 MPG and actual MPG achieved. If your car averages more than 30 MPG you receive a credit for every mile at registration renewal.

Full size trucks and cars already have different speed limits. How will variable speed limits be enforced, by means of engine control software. You plug the car into the engine diagnostic port as for a smog check and download the average speed and fuel consumption data... Fees owed have to be paid to renew your vehicle registration.

I am just trying to illustrate that there is no one-size-fits-all "solution". Be careful what you wish for: You call for a 55 MPH limit. Another group with more influence may get a 35 MPH limit passed. Both will annoy the hell out of anyone who has to cover long distances, but perhaps that is your goal...

That's a slight exaggeration, but it'd never work.

Those who break that speed limit by over 10 get triple ticket pricing. Hopefully when assholes trying to go 70 on a 50 highway are paying 300-500 per ticket they will stop.

Or you can tax the hell out of fuel.

For the long boring streches of highway cars and trucks could have autopilots.

If you don't like it, take the train.

...but the automakers "don't want to take the fun out of driving." (quoted from a NYT article some years back...no link.) That would be quoted from the types that never have to drive in traffic on a daily basis, and live in the fantasy worlds of their CGI-laden commercials.

Let's see you jump from rooftop to rooftop in a car!

I drive slower than X, or the limits should be lower than Y.

Why not have a man with a flag run in front of the car to warn pedestrians?

It made sense then, and it's always made sense.

And whenever possible, I get off the freeway and take an older route where I'm less likely to get killed....

I am under the impression that the most likely place to get killed in a car is on a two lane blacktop. Two cars meeting feet away at closure rates of 100MPH is far worse than being on four lanes divided with 10-15MPH difference between adjacent vehicals.

Seems like they're already slowing down on their own.

Saves money, saves lives, reduces emissions and conserves a limited resource.

Win, win, win, win, win...........

A little slower won't matter, but if they have to stay overnight and deliveries are late by one or more day, they loose a lot of money.

From what I have seen trukers are paid something like 40 cents per mile. Cut their speed you cut their pay. So maybe if we force truckers to slow from 65 to 55 we should in a show of support reduce our own pay by 16% as well.

50 miles away, and the US, State, and County highways are all still set at 55mph limits, I normally drive 55-60 anyway. :shrug:

I remember when all the Interstates started jumping up to 65, though, and since then many places are going to 70 or more. I wouldn't have a problem with the Interstate system going back to 65mph nationally.

My 94 Z28 runs at lower rpms at 75 in 6th gear than it does at 55 in 5th.

I pollute more at 55 than than I do at 75. I am doing my part for the environment.

> My 94 Z28 runs at lower rpms at 75 in 6th gear than it does at 55 in 5th.

So put it in 6th at 55 and really do something "for the environment" ...
:shrug:

Better still, put it in reverse at 55 and solve the problem for even longer.
:P

> I pollute more at 55 than than I do at 75.
> I am doing my part for the environment.

Redneck Racers Going Green eh?

And to think that I thought "The Dukes of Hazzard" was fiction ...
:shrug:

"So put it in 6th at 55 and really do something "for the environment" "

Makes sense right?

Well the gear ratio for 6th makes it an over drive gear at .62 to 1. With my large cam, my car would spit more unburned fuel out the tail pipes then it would burn it. And it would drive like crap. Operate in the powerband for efficienty.

"Redneck Racers Going Green eh?"

Not sure where you are going with this one.

"And to think that I thought "The Dukes of Hazzard" was fiction ..."

You were wrong

... the "redneck" was unnecessary, it just came out with the "DoH" image
that your post put in my mind ... sorry about that.

> With my large cam, my car would spit more unburned fuel out the tail pipes
> then it would burn it.

Can you please help me with this? I don't see how (other than briefly
through revs over-run during deceleration) you would be "spitting unburned
fuel out of the tail pipes" unless your engine was really out of tune
(e.g., along the lines of running with the choke out). (I'm not arguing
the point, just confused by it - TIA.)

:shrug:

Think about how a vacuum system works. Just like a motor. With a larger cam, like mine, there is overlap between the intake valve closing and the exhaust valve opening. The higher rpms create more vacuum keeping the fuel in the cylinder. the motor makes more power at 7500 rpm than it does at 1000 rpm because it is burning more fuel and converting more fuel energy into useable power.

I am by no means an expert, but I konw that my car gets better gas milage at 2000 rpm than it does at 800