The optimum engine fuel effciency speed is supposed to be 45-55 mph.
We had a National speed limit of 55 mph for years.
Demand for fuel would go down.
Imports from the volitile Middle East would be reduced.
So.
Why ain’t we drivin’ 55?
Because Sammy Haggar doesn’t want to.
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Okay, realistically, I think it’s because public roadways aren’t built for 55. They’re designed so that speeds between 65 and 75 are safe. So people drive that fast. I don’t believe it’s any more complicated than that.
There are people considering doing just that, including Hillary Clinton.
We did that for many years and people hated it. I don’t think anyone pines for the 70’s in that way and people still have the option of driving 55 if they really want to. Most people are willing to pay extra in gas so that they can drive faster.
I asked my husband this question last weekend, on a trip to South Dakota. We stayed off the interstate so we managed to do 55 without causing slowdowns.
Even in areas with miles of open roads and flat terrain, there are hazards (deer, bad tires, potholes, etc.) that should make it worthwhile to slow down a bit.
I feel for people who travel interstates and freeways and need to keep up with the traffic – they’re in a bind if they want to slow down, or even do the speed limit. 
Engine speed is measured in RPM (revolutions per minute). This is related to vehical speed by the gear ratio. It was true back in the Seventies and early Eighties with high C[sub]d[/sub]'s and three speed automatics that cars were significantly more efficient at lower speeds, but with modern electronically controlled high efficiency automatic transmissions and low drag profiles the difference in efficiency between 55mph and 65mph is small. Large trucks and SUVs are less efficient, but even most of these–save for those which for which part of the appeal is their ostentatiousness–are more efficient at highway speeds than their predecessors. Cars are, in fact, most inefficient not when driving on the highway but when accelerating and braking in traffic, and using a hybrid electric type of system (particularly one that regenerates braking energy) would do substantially more to increase efficiency.
The more compelling argument for reducing speeds is that it reduces the severity of an accident (although, curiously, as little impact on the incidence of accidents except in inclement conditions). That being said, few peopel are going to be in favor of reduced speed limits, and particularly those who commute long distances daily.
Stranger
Because time has value, and many, probably most, people would rather spend the money for gas than spend the time for slower traveling.
To put this another way, we’d rather bitch and moan about high gas prices than slightly inconvenience ourselves to save gas.
Complaining is easy, taking steps to fix the problem isn’t, so we don’t do it.
It’s actually quite easy to slow down a bit.
The fact that relatively few people do so argues GaryT’s point: they believe the value of their time is greater than the money saved.
What’s your “small” in the above parapgraph?
Less than 10%, i.e. for a car that gets 25 MPG, a difference of 1-2 MPG. I realize that this isn’t “small” if you added it up across the entire population of drivers, but you have to contrast this with the opportunity cost. After all, if you have to drive home slower you might miss a few new pointless and ultimately unsatisfying revelations on Lost.
We could save a lot more fuel if we just told all the people who aren’t doing much more than moving paper from one side of the desk to another (a category in which your humble narrator finds himself suited far too often) to just stay home, but then you’d have to offset the gas savings with increased peak use of energy from everybody watching “As The World Turns” which might overload the grid. Regardless, modern civilization is doomed, and the collapse will happen sometime between next Thursday and AD 2472, with a 90% confidence. 
Stranger
Not necessarily. That depends on the final drive ratio of the auto relative to the peaks in the power and torque curves of the engines, and coefficient of drag of the car. Since the 55 mph was last prevalent, these things have changed. The Cd of most cars has been reduced and the final drive ratio has been changed so that the engines are cruising at lower RPM that is more likely on the left hand side of their power curve. So, the fuel savings gained by dropping the speed limit would not be as great (per car) as it was in the '70s.
No we didn’t. We had most states set their maximum speed limits at 55 mph because the federal government bullied them into it by threatening to withhold federal highway funds.
I can’t argue with that, but the goodness or badness of that it not a GQ subject.
You go first. I’m not just giving you a flip answer here, but why didn’t you ask, “Why ain’t I driving 55?”
OK.
I did.
I’ve been driving 40-55 mph on a non-interstate for several years.
It’s also 5 miles shorter each way than the Interstate. 50 fewer miles driven per week, at a slower speed.
And yes, my milage has improved, noticably.
And it sucked the sweat off a dead dogs… :eek:!
It was, technically unconstituional per the 10th Amendment, and the state of Nevada was planning on fighting the limit in federal court. This was prior to the minute’ raise to 65 the feds allowed in 1987.
The police department I worked for in the early 80’s was stupid enough to accept radar units that were provided via federal funding. We had a 55 zone that was previously 70. By accepting that equipment we had to keep all sorts of stupid reports and matrix about how the units were used (freeway vs city streets) average speeds of violators, vehicle counters on the roads, and all sorts of happy horseshit. All this to enforce an extremely unpopular law. And it was very unpopular. Nobody, but nobody obeyed it. Everyone went at least 10 over. The sales of radar detectors, scanners, and cb radios went through the roof. Sales of these items dropped like a rock after the national limit was repealed.
Can you name any other law where otherwise law abiding people spend hundreds of dollars just so they can break it?
The national speed limit is a bad idea that hardly anyone wants. And here is my “cite”:
You will notice, Bosda, that after the national limit was completely done away with in 1995, that not a single state went back to 55, and most states raised their limits in excess of 65 to 70, 75, and even 80 mph. The people have spoken via their state legislatures: 55 sucks.
If you want to save yourself some fuel, by all means slow down. But stay out of the left lane. A citation for impeding traffic is just as expensive as one for speeding, and, in my opinion, much more fun to write!
Every state had 55 as their limit during that time. I don’t know of any that had it prior to the double nickel (Hawaii, maybe?
) Some states were creative in how they enforced it, giving $5 “energy wasting” fines on the freeways instead of speeding tickets.
Exactly!!
I’m tired of hearing how driving 55mph saves gas when most of the communities I drive in (Los Angeles area), have their traffic lights set so that it is nearly impossible to drive and hit more than two green lights in a row. Am I to believe that driving 70 instead of 55 wastes more fuel than accelerating to 40, slowing down, idling for 1-2 minutes, repeat every 200 ft?
[hijack]Incidently, this is my argument when the guv’ment complains about exhaust pollutants. Why don’t the communities try to reduce pollutants by allowing efficient travel rather than hindering it?[/hijack]
I don’t think it’s commuting as much, as shipping.
Sure it would suck for a person that commutes 40 miles. 10 mph slower would add what, 8 minutes to the trip? Not insignificant I guess.
Also, road trips. Driving through near nothingness at 55 mph gets old, real fast.
You sir are my hero. If we ever meet the coffee and the donuts are on me.*
*Or the beer seeing how is is always 5 O’clock somewhere.
Aside from the other reasons mentioned, the fact is that the 55 mph speed limit didn’t necessarily slow people down. Studies have shown that vehicle traffic flow usually finds its own speed, and that speed is set by the density of the traffic and the driving conditions. If you changed the speed limit on I-95 to 25 mph, do you think the flow of traffic would slow down? Only if you put speed cameras on the road, advertised them, and then brutally enforced every speeding infraction. Over time, that might slow people down, but then they’d come to hate you.
Another interesting study shows that people drive faster when they think their cars are safer. Put an airbag in a car, and people feel more protected and therefore drive faster. So if you want to slow everyone down, you could pass a law mandating that every steering wheel have its airbag replaced with an 8" spike aimed at the driver’s heart.
That sounds silly and flippant, but a variant of this has been implemented in Wiltshire in Britain - all the lane lines were removed from the roads to scare drivers into driving slower and more safely. Traffic engineers call it ‘psychological traffic calming’. Make driving fast seem more dangerous, and people will slow down.
To expand on what Stranger on a Train said about efficient speeds - the most efficient speed for a car is different based on its drag profile. For some vehicles it may be 45 mph, and for others it may be 75mph. But the difference between 55 and the other speed limits today is probably trivial, especially when you factor in non-compliance. In some areas it may even be counter-productive if the slower speeds create congestion and cause more braking/accelerating.
A much more effective way to decrease average trip fuel consumption would be to eliminate congestion. You could do this by having road tolls, congestion surcharges, or just by building more roads. In some areas, it may make sense to eliminate bus and carpool lanes - they were put in to encourage people to take alternate transport, but in many places these lanes are mostly empty. Opening them to all traffic might ease congestion significantly, which would cut down on the total amount of fuel the mass of commuters use to move around.
I drive 40 miles each way to work, almost all of it freeways outside of town. When the price of gas was around $2.00, average traffic speed was just slightly below 80mph. (posted speed limit is 70mph). Every time the price of gas has gone over $3.00, the average speed has dropped to 70 or lower.
So people are driving slower to save gas.
Preach it Brother! 
Why don’t many of us give up our gas hog SUV’s and drive more fuel efficient cars?
Why not move closer to work?
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Bosda Di’Chi of Tricor**: what kind of car do you drive? How fast do you drive? How far is your commute?