Senator John Warner's plan for helping with high gas prices

[Surlethe]

Back to the question: will lower speed limits increase congestion? If a road is pretty much at capacity (most cars are less than 2 seconds away form the car in front of them) at speed x, then the road will clearly be over capacity at speed x-10, and so I'm pretty sure there's going to be more congestion. The same amount of cars want to go through, but less can pass through per time unit now.

The distance between cars will decrease as the speed decreases, so shouldn't that balance out the decrease in speed?

Edit: No, that's not relevant. What is relevant is that the time between cars stays the same, so traffic flux decreases. However, the fact that the time between cars stays the same would seem to imply that the road stays at capacity; after all, wouldn't you expect fewer cars per unit time when the speed they travel at slows down?

[White Haven]

But that leads to having more cars on a given stretch of road at any one time, which means that when the inevitable wave of brake-lights from any cause appears, it propagates through more drivers, all of whom are braking more than is strictly necessary for safety.

[Mad]

The distance between cars will decrease as the speed decreases, so shouldn't that balance out the decrease in speed?

Edit: No, that's not relevant. What is relevant is that the time between cars stays the same, so traffic flux decreases. However, the fact that the time between cars stays the same would seem to imply that the road stays at capacity; after all, wouldn't you expect fewer cars per unit time when the speed they travel at slows down?

That's not what happens, though. Drivers don't stay exactly 2 seconds apart when traffic gets heavy; they start getting closer to each other. Remember: the same amount of people are driving home from work, but now they road gets congested faster because the same amount of cars are entering, but cars are leaving at a lower rate.

[Patrick Degan]

55mph worked as a limit in 1974 because car engines sucked shit with carburetors that spewed raw gas right out the tailpipe while no one cared about aerodynamics; today a very great many cars need to drive faster, quite a few as high as 80mph, to get optimal fuel economy. But you know it figures that the dumbshits we call congress have no comprehension that things can change in a mere 30 years

Yes. I've had to take several road trips back to New Orleans since the flood, and for all but one of those I've used my mum's 4 cyl Dodge Stratus because it gets better mileage than my Buick, and I've found it getting around 31mpg or a bit better running at 75mph. This last trip the mileage was a bit worse because I had to pass through a long stretch of road construction which slowed traffic to 55mph and had less than a half tank when I pulled into Meridian to top off. Not facing that on the way back and able to cruise just about the whole way I was doing better on fuel.

[The Duchess of Zeon]

Only 31? Hmm. Our Corolla's managed 36mpg at 75mph continuous.

[Patrick Degan]

Only 31? Hmm. Our Corolla's managed 36mpg at 75mph continuous.

About average. It's hilly country on the drive between Gadsden and New Orleans and through Laurel, MS you really do have to slow it down to 50 because of sharp S curves going through town. You also have to drop down to 60 going through Birmingham and Tuscaloosa. The Stratus is also, I think, a slightly larger model than the Corolla. On some stretches though it would get up to around 39mpg, others it would drop to around 29-28mpg. I know I'm doing good on mileage if I'm still above a half tank when I hit Meridian, which is the halfway point on the drive.

[Starglider]

Today a very great many cars need to drive faster, quite a few as high as 80mph, to get optimal fuel economy.

Really? I find that moderately surprising, since drag is proportional to speed squared and rolling resistance is also worse than linear. Can you cite any evidence for that figure?

My Audi A6 seems to get a fairly even 40-42mpg (UK) from 50mph to 60mph. It goes down rapidly from there, to 30mpg at 80mph. Thus I drive at 60mph unless I have a pressing need to be somewhere. It helps that my new car is really pleasant to be in, reducing the motivation to get the trip over with compared to the 1980s junk I had when I was young.

[Surlethe]

The distance between cars will decrease as the speed decreases, so shouldn't that balance out the decrease in speed?

Edit: No, that's not relevant. What is relevant is that the time between cars stays the same, so traffic flux decreases. However, the fact that the time between cars stays the same would seem to imply that the road stays at capacity; after all, wouldn't you expect fewer cars per unit time when the speed they travel at slows down?

That's not what happens, though. Drivers don't stay exactly 2 seconds apart when traffic gets heavy; they start getting closer to each other. Remember: the same amount of people are driving home from work, but now they road gets congested faster because the same amount of cars are entering, but cars are leaving at a lower rate.

Oh, I see what you mean. Thanks.

[Ma Deuce]

Only 31? Hmm. Our Corolla's managed 36mpg at 75mph continuous.

A Stratus is a midsized car though, with 2.4L under the hood (comparable to the Corolla's bigger brother the Camry), while the Corolla is compact, so 31 MPG @75mph is actually pretty good for that type of car.

Anyway, even without a new limit, gas prices are encouraging drivers here in Ontario to slow down on the highway. Most people on the 401 usually drove at the de facto speed limit of 120 km/h, vs. 100 km/h as posted, but now more people are driving at the limit.

Of course, people have also taken to doing things far more dangerous than speeding in order to save gas, such as running through red lights and stop signs, and taking turns without slowing down at all.

[American Infidel]

Screw John Warner and this "plan" to fleece the nation's drivers. It's all about getting more of my/our money to the government and the insurance companies.

[The Duchess of Zeon]

Screw John Warner and this "plan" to fleece the nation's drivers. It's all about getting more of my/our money to the government and the insurance companies.

Well, the whole thing is rather stupid when the issue is vehicle size and absolute consumption, I'll grant (particularly with modern aerodynamics), but why ascribe to malice what may better be called stupidity?

[American Infidel]

Well, the whole thing is rather stupid when the issue is vehicle size and absolute consumption, I'll grant (particularly with modern aerodynamics), but why ascribe to malice what may better be called stupidity?

I don't believe that a desire to help motorists is the true motive. Too much money is at stake.

[Darth Wong]

Of course it's not about helping motorists. It's about trying to slow down fuel consumption so we can buy time to find a solution to the fuel problem. It won't work, but that's beside the point.

[The Duchess of Zeon]

The goal of nobody ought be to "help motorists"; it should be to eliminate them.

[Admiral Valdemar]

I had also heard that the perfect average speed from some engineering journal study was around 40 MPH. I'll have to find that again, because it's a optimum between engine efficiency and loading of the highways themselves.

[Slacker]

In New York, the state speed limit is already 55, and cops won't even stop eating their donuts unless you're doing a fair bit over 70. I've had cops flash their lights at me at night because, at ~70, I was going *too slow* for them. Now, if it's the end of the month, you want to be a bit more careful, but generally it's not worth their highly overpaid time.

[Sikon]

If lower speed limits added on average X minutes of extra time traveling for the average person per 8 hours worked, if that time was valued Y fraction as much as time at work, the equivalent cost would be roughly on the order of X * Y * $300 billion per decade.

Warner cited studies that showed the 55 mph speed limit saved 167,000 barrels of oil a day, or 2 percent of the country's highway fuel consumption

Given the tendency for modern vehicles to be more aerodynamic and optimized for higher speeds than those of the 1970s, less than 2% savings (if any) would be the case now. For the U.S. doing such, world oil consumption would be reduced by under 0.5%, having only a limited degree of effect on oil prices in the world market and hence the U.S. market. Actually, world oil consumption would tend to change even less. Slightly more would go to other countries rather than the U.S. in the new market equilibrium, but consumption is always equal to world oil production, which would be close to the same as before.

Mainly, a 55 mph U.S. speed limit would have little effect on oil prices. But to the degree (if any) that it actually reduced oil prices, such would slightly slow the expansion of alternative fuels and synthetic production by somewhat reducing the competitiveness of such in the marketplace.

Instead put $300 billion into synthetic fuel production, and the degree of U.S. energy independence would be greatly increased. Or put $300 billion into nuclear power plant construction, and the resulting ~ 100+ gigawatts of new nuclear power could convert the U.S. power supply from 20% nuclear to around 50% nuclear.

But reducing speed limits to 55 mph? Such could give the feel-good illusion of taking enough action while doing very little beneficial. Meanwhile the cost of the lost productivity, time inefficiency, and nuisance may be equivalent to hundreds of billions of dollars over the decades as previously suggested. The U.S. economy is $130+ trillion/decade, so even a fraction of 1% change in productivity is an enormous amount.

Admittedly, changing the speed limit could result in fewer highway fatalities (although many come from drunk and irresponsible drivers who often wouldn't follow the new speed limit anyway). However, that is better managed by speed limits varying as locally appropriate than having a simplistic nation-wide 55-mph cap. For example, if driving down the interstate in the middle of desert in Nevada with little traffic, it's safe enough to go much faster than 55 mph, as the local speed limit should reflect.

If going to create a nuisance for drivers anyway, an increased gas tax would be much better. At least such would provide revenues proportional to its cost, rather than mainly just having drivers spend more time on the road rather than being at work or recreation, mostly benefiting nobody.

[gtg947h]

Today a very great many cars need to drive faster, quite a few as high as 80mph, to get optimal fuel economy.

Really? I find that moderately surprising, since drag is proportional to speed squared and rolling resistance is also worse than linear. Can you cite any evidence for that figure?

My understanding is that rolling resistance is typically constant, regardless of speed... assuming normal conditions where you aren't overheating the bearings or anything like that. But I don't think that factors in things from deformation of the tire or aerodynamic effects from a spinning cylinder.

And even though drag is proportional to airspeed squared, fuel consumption isn't linear with engine power output. It takes some amount of fuel just to keep the engine running

[Knife]

I think, for once, the market might take care of the conservation part on the consumer side. SUV sales have plummeted and Toyota can't make Priaus's fast enough. Active grass roots like campaigns to slow down and save gass are everywhere and I've noticed it on the freeway. People aren't driving across the country as much on vacation this year which has a lot of businesses uppity. People are getting the point now, what we need is the politicians NOT to give us a quick fix.

No more rebates and no more 'drill here real quick and you can go buy a new SUV'. We need the politicians to start making decisions based on no oil, not based on keeping up the status quo.

[Sikon]

Regarding car efficiency versus speed:

Quite a large amount of the losses for a vehicle are internal frictional losses.

A simple illustration of this is observing how much longer one's vehicle can coast at high speed if one shifts into neutral first (rather than just taking one's foot off the gas pedal but staying in gear). That merely eliminates some of the ordinary frictional losses, but even such makes a very noticeable difference.

With a manual transmission, I've often seen good results from going fast, shifting into neutral, coasting for a long time until speed drops by 10 mph, then applying a little gas again, and repeating. It's especially good going downhill, although judgment must be made depending on the local traffic and road as to whether or not that is a safe option on a particular hill; one doesn't want to speed out of control.

Of course, this is mentioned for illustrative purposes only. Although able to much increase gas mileage, apparently coasting is said to be illegal in some states for safety and control reasons; one can be more dependent on the reliability of brakes.

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To illustrate a principle with an extreme example, any vehicle would get terrible miles per gallon if one drove it around at 5 mph. By the time one had spent 14 hours to travel 70 miles, one would have consumed vastly more gasoline than if one traveled that distance in 1 hour at 70 mph, even though the former slow speed had vastly less loss from air drag.

The engine consumes a substantial amount of gasoline even when just idling. Even when just 1000 rpm, there's a lot of power demanded to keep it going.

For the average vehicle, peak fuel economy went from being at around 40 mph in 1973 to become around 50-55 mph in the late 1990s. And it declines only slowly at first for speeds a little greater. For example, the average vehicle in 1997 could get better fuel economy at 60 mph than at 40 mph.

By now, another decade has passed. In 2008, with still fewer old vehicle designs around than in 1997, the situation should be still better. Probably many of today's vehicles obtain peak mpg at 60 mph or higher, and going at 70 mph should often give very similar mpg to 55 mph. Eventually mpg decreases drastically, but it can take speeds well beyond that to have large decline, depending on the particular vehicle.

[Admiral Valdemar]

I think, for once, the market might take care of the conservation part on the consumer side. SUV sales have plummeted and Toyota can't make Priaus's fast enough. Active grass roots like campaigns to slow down and save gass are everywhere and I've noticed it on the freeway. People aren't driving across the country as much on vacation this year which has a lot of businesses uppity. People are getting the point now, what we need is the politicians NOT to give us a quick fix.

No more rebates and no more 'drill here real quick and you can go buy a new SUV'. We need the politicians to start making decisions based on no oil, not based on keeping up the status quo.

Fortunately, America is keen and ready to disprove your thinking. Hooray for irrational actions!

[Edi]

So they were all for conservation etc as long as they did not have to pay for anything or change their lifestyles at all, as usual.

[Admiral Valdemar]

So they were all for conservation etc as long as they did not have to pay for anything or change their lifestyles at all, as usual.

Yeah. Do as I say, not as I do. It's okay for those horrible Third Worlders to cut back on three meals a day to two and forego that first car, but if you take my SUV or plasma telly off me, I'll be pissed.