Re-Institute National 55mph?

[instarx]

Originally Posted by getnpsi

with the rumors of all the new obd tricks the government wants, cars will have transponders to report failing emission equipment. they should look into some sort of feedback where your car lights up in the dash when your speed or driving style isnt acceptable. more mpg computers standard will make people slow down on their own

Many years ago in Singapore I asked my taxi driver why all the taxis had small lights on their roofs. They were to let the police know that the car had gone over the maximun Singaporean speed limit so the police could give them a ticket.

Being an American I asked if the drivers didn't just disconnect them. "Oh, No"!, was the reply. It seems that caning is very painful.

Old Volvo's of the 70's era in the US used to have a speed alarm that would buzz if you went over your set speed.

In college there was the rumor that if you got between two points on the New Jersey Turnpike in too short a time they would hand you a ticket when you paid! I'm pretty sure that was just urban myth. I now know that most states don't really want drivers to go the speed limit - it reduces the carrying capacity of the road too much.

[dcb]

Originally Posted by Bror Jace

So, exactly how much would we save by speed limit alone? And aren't there better ways to save that (I'm guessing relatively small) amount of fuel?
...
Heck, if we could just get people to stay bellow 65mph we'd probably save a million barrels per day.

Your post would seem to contradict with itself?

There's plenty of data, it all says the same story. The laws of physics cannot be wished away and above a certain point, speed kills mpg, period, full stop, end of story.

You don't have to look very hard to see some test results:
Speed kills: testing MPH vs. MPG in top gear - MetroMPG.com

You can reduce idling too certainly, plenty of other things you can do to save gas as well. Tips to improve your Gas Mileage

The arguments about enforcement apply to each and every single traffic law (and most laws in general) so are not especially relevant here.

[instarx]

IN the 70's the 55 mgh speed limit was in response to a serious oil shortage due to an oil embargo. We really were running out of oil that we needed for more important things than driving around. Remember that there was no strategic oil reserve back then and the country was basically living from week to week between oil shipments.

Today there is no oil shortage - it's just expensive. It seems to me that price is a much better way to control consumption. Traffic in my area has dropped considerably since gas hit $4 per gallon. I don't see as many SUV's and large pick-ups driving around or in parking lots. I see many more bicycles and scooters. None of those things would be promoted by a 55 mph speed limit.

[trikkonceptz]

There are so many good points being thrown around here, it is hard to take a side. The basics though are true, slowing down will save you gas. That will not happen until the price of gas cuts into more than just spending cash.

If the speed limit is dropped back down, it will likely happen with electronic monitoring. Meaning devices like my Sunpass which is a electronic toll meter, can also be used to read speed between distances and issue citations in that way.

That however raises the questions of whether or not speeding is a right ... Because if it wasn't wouldn't our cars be federally governed to the current speed limits?

Like I said its a fine line, in the end we may need to adpot an autobahn hwy for long distance driving with very few stops and limit the speeds on commuter hwy systems. This will not have an easy answer and will no doubt piss many people off.

For now I treat driving 55 like its my little secret, because when I tell anyone how well I'm doing with my mileage and they ask how, the first thing I say is, "I slowed down". That answer alone puts the sour candy look on their faces, which I cherish, so until gas hits $8.00 a gallon, I do not expect any revolutionary driving changes in our ignorant public.

[jamesqf]

Originally Posted by Bror Jace

Repeating my request from a page or more ago, has anyone measured (gallons per hour OK) fuel consumption rates with a scangauge at 55mph vs 65mph?

Not with a ScanGauge - I've found the fuel consumption measurement is not really accurate on mine - but with the built-in real-time mpg meter in my Insight.

As best I can tell, there is no simple 1:1 relationship between speed and mpg. There are times & places where I can be going 65 and getting 120-150 mpg, other times I can be going 55 and getting 55 mpg - both on fairly level roads without much head or tail wind. There are places - I680 through Sunol (SF Bay Area) for one - where going 65-75 gives better mileage than 55, because I can stay in 5th over the hills instead of dropping to 3rd. And of course there are all the long downhill runs where I use no gas at all, regardless of the speed I travel. (I have a picture somewhere of my trip gauge showing 150 mpg for a 70 mile trip - the trick is to start at 8500 ft, and finish near sea level :-))

All this is just one of the many reasons I don't like the idea of a mandatory 55 mph limit. It's a too-simplistic, one size fits all attempt at a solution.

[tjts1]

Originally Posted by instarx

I now know that most states don't really want drivers to go the speed limit - it reduces the carrying capacity of the road too much.

Exactly.
55mph speed limit will increase fuel consumption by causing congestion.

[dcb]

Originally Posted by jamesqf

There are times & places where I can be going 65 and getting 120-150 mpg

Is yours a typical vehicle? Is this an instantaneous reading or a real one?

And with an appropriate following distance, there is no change in throughput.

[instarx]

Just this week I did some mileage runs with the internal computer on my Volvo and over a 24 mile measured course (all variables controlled as much as possible) I got 28.5 at 70 mph and 30.9 at 65 mph. Not 65 vs 55 like you asked, but useful info. I strongly suspect it would have been over 33 mpg at 55 but tht is a guess.

Some specs:
Speed controlled by cruise control
no traffic, no wind
windows closed, no AC
A-A-B-A

These numbers were just baseline numbers to allow me to evaluate a front air dam I was adding. Just FYI, mileage improved to 30.7 at 70 and 32.3 at 65 with the air dam, so I'm keeping it. Looks good, too.

[Bror Jace]

dcb, thanks for the link to metrompg's site. Some information I hadn't seen before ... but I'm still not impressed with the savings. Unless it's at least 10% or more, I just don't see a compelling reason to see a national law limiting speed ... especially when more fuel is wasted in other ways.

"The arguments about enforcement apply to each and every single traffic law (and most laws in general) so are not especially relevant here."

Not true. Most laws are about right and wrong, harming others, etc ... This one would be specifically about economy ... and if you can't get compliance (a great deal of it) it does absolutely no good at all.

jamesqf, thanks for that tidbit ... and I agree that it depends, depends, depends ... When driving for maximum mileage, I will exceed the speed limit going down a hill to build up cheap energy to coast or climb the next one with a reduced penalty. In that sort of instance, I can get better economy than if I set the cruise at 55mph the whole trip.

instarx, Thanks for your tidbit as well. As speeds go up, the penalty increases so I would expect the economy difference between 55mph - 65mph to be just slightly less than the difference between 75mph and 65mph. The number is significant if you are an economy nerd like most of us here ... but not enough to warrant a national law (IMHO).

[getnpsi]

congestion is caused by many people driving 75+ right into a construction zone and slamming the brakes, causing a 10 mile ripple effect--whereas if the first cars reaching the zone would have been slower no one would have lost their momentum.