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I fail to understand how changing the posted speed limit will make any difference when the actual speed of traffic on highly congested Bay Area freeways is well below 55 mph.
a) Only about 1% of American roads have speed limits in excess of 55mph now, so eliminating them would hardly change anything--even if we assume people will obey the new speed limits.
2] You need to take gearing into account: a car travelling at 45mph, for instance, in 3rd gear will burn considerably more gasoline per mile than one travelling 45 mph in 4th gear....Semi trailer trucks can have as many as 18 gears and limiting them to 55mph can cut their mileage in half...
For cars, travelling at 55 has the automatic transmission "confused"-- slowing down just a little from 55 will have it often shifting needlessly into lower gear. (A 60 mph limit would make more sense-- little difference in gas mileage and less up & down shifting in actual driving conditions.)
c) If we really want to speculate, we could argue that slowing freeway traffic down will cause the number of cars on the road per mile per hour to increase, leading to more traffic jams and more sitting at idle in rush hour traffic-- way more fuel wasted.
This is one of those "let's do something so it looks like we care" movements that is not very well thought out.
What? The mileage in my 18 wheeler peaks at around 55, which is about as low as it can comfortably maintain top gear.
And given that cars in the US are almost entirely automatics, I don’t see how anyone is accidentally a gear down at 55. Most vehicles are in top gear well before 55, usually somewhere under 50.
Given the severity of rush hour in the Bay Area...55 won’t make much of a difference! I hear from folks who still live there that it’s gotten worse in the 15 years I’ve been away.
OK but what if you drive a Tesla. Then what is your justification?
He'll argue that you use less battery charge and it somehow impacts what happens at the power station.
But that would be incorrect, as well.
55 MPH is an old number calculated when cars had 3 and 4 speed transmissions, and weren't very aerodynamic. Perhaps some people think it's still the magic number because that's usually the lowest speed at which automatics drop to their highest gear, thus highest efficiency.
This might not be looking at the whole picture, though. Imagine an 8-lane, mostly straight interstate. If my 9-speed transmission lets me cruise at 55 MPH @ 2,000 RPM, but also lets me cruise at 65 MPH or 75 MPH at 2,000 RPM if I want, the faster speed would let me spend less engine runtime spinning 2,000 RPM (faster route, shorter trip) than putting along at 55 MPH.
Back in the 70s and the oil embargo, the typical US car was 55oo lb and sported a V8 that got 15mpg. If you left your car running while filling up, you pulled away with less gas than you pulled in with. Goose the gas pedal to rev it up and it was like flushing a toilet-- the accelerator pump dumped 2 oz of gas down the throat at a time.
Now cars weigh 2500 lb, have only 4 or 6 little cylinders and miserly fuel injection. They all look alike because they're computer designed using the same formula for aerodynamics. Back then gas mileage fell noticeably at speeds above 55-60. Today it doesn't start to matter until 65-70mph.
BTW- except for the OP, none of us, thankfully, have mentioned "carbon footprint" the politically motivated none-problem. We should be conserving fuel specifically and energy generally for the sake of conservation.
Waste not, want not.
The falling MVA death rate started several yrs before the embargo and lowered speed limit, and continued for a decade as more & more autos were made with disc brakes. It's not like there was a sudden fall in death rate with lower speeds.... If you're old enough to remember-- driving a 5500 lb Oldsmobile with a 440cu in V8 and drum brakes could get inadvertently exciting at times.
15mpg? That would have been *good*.
My '75 Gran Torino with the 351 Cleveland was lucky to get 10mpg. And my 1970 AMC Ambassador SST with the 360/4bbl, well, if you put your foot in it you could almost see the gas gauge dropping...took 3 months for me to figure out that the odd 'roar' was the secondaries opening up...
Wow OP, epic fail. Not one person thinks 55mph is worth consideration. Mandating more cars be electric might actually help the environment, though not the Auto makers.
Don’t feel bad, the thought counts. Big proposals like yours just needs to be thought out more.
55 MPH is an old number calculated when cars had 3 and 4 speed transmissions, and weren't very aerodynamic. Perhaps some people think it's still the magic number because that's usually the lowest speed at which automatics drop to their highest gear, thus highest efficiency.
This might not be looking at the whole picture, though. Imagine an 8-lane, mostly straight interstate. If my 9-speed transmission lets me cruise at 55 MPH @ 2,000 RPM, but also lets me cruise at 65 MPH or 75 MPH at 2,000 RPM if I want, the faster speed would let me spend less engine runtime spinning 2,000 RPM (faster route, shorter trip) than putting along at 55 MPH.
That's my argument.
That's the basic argument from the practical standpoint. The wind resistance advantage gained by driving slower is lost when you consider engine speed/gearing.
Quote:
Originally Posted by Zymer
15mpg? That would have been *good*.
My '75 Gran Torino with the 351 Cleveland was lucky to get 10mpg. And my 1970 AMC Ambassador SST with the 360/4bbl, well, if you put your foot in it you could almost see the gas gauge dropping...took 3 months for me to figure out that the odd 'roar' was the secondaries opening up...
You know there's more than "off" and "floored" positions for the accelerator pedal, don't you? The Pantera with 351C was scary. Diapers not required, but highly recommended.
Quote:
Originally Posted by jcp123
What? The mileage in my 18 wheeler peaks at around 55, which is about as low as it can comfortably maintain top gear.
And given that cars in the US are almost entirely automatics, I don’t see how anyone is accidentally a gear down at 55. Most vehicles are in top gear well before 55, usually somewhere under 50.
Given the severity of rush hour in the Bay Area...55 won’t make much of a difference! I hear from folks who still live there that it’s gotten worse in the 15 years I’ve been away.
In theory, your optimum mileage is driving at 55 (Many OTR big rigs have gearing with longer legs than yours, so optimum speed is considerably higher) but in the real world, how often do you get to hold it right at 55? You try it, but traffic slows up a little and you lift off and slow a little and then either lug it & risk damage or down shift to get back up to 55.
Autos with automatic tranny have either 3 or 4 gears, but either way, final drive is 1:1. At about 45 mph the tranny becomes locked ("over drive"; a misnomer). Just like the problem with the big rig, if traffic slows from 55, the tranny may sense a need to down shift. At 65, a minor lift and slowing probably won't cause that.
Hilarious. People are treating every freeway like the autobahn. There are barely any cops and the left want fewer. There is nothing YOU can do to stop anyone speeding anytime soon. Screwed the pooch the libs did on this one.
When I drive in and going home my average speed is 70 in and 75 back. I average 23 mpg out of a big 4200 pound tuna boat on four wheels. I rarely see a cop on the freeway anymore. And when I do they are gong faster than I am.
Quote:
Originally Posted by jcp123
What? The mileage in my 18 wheeler peaks at around 55, which is about as low as it can comfortably maintain top gear.
And given that cars in the US are almost entirely automatics, I don’t see how anyone is accidentally a gear down at 55. Most vehicles are in top gear well before 55, usually somewhere under 50.
Given the severity of rush hour in the Bay Area...55 won’t make much of a difference! I hear from folks who still live there that it’s gotten worse in the 15 years I’ve been away.
Not everyone drives a auto. My diesel has a ZF6 with a Gearvendors overdrive so I can split gears. At 55 I would be splitting third probably lugging the hell out of fourth spewing coal because I’ll drop out of my powerband.
When I drive in and going home my average speed is 70 in and 75 back. I average 23 mpg out of a big 4200 pound tuna boat on four wheels. I rarely see a cop on the freeway anymore. And when I do they are gong faster than I am.
Not everyone drives a auto. My diesel has a ZF6 with a Gearvendors overdrive so I can split gears. At 55 I would be splitting third probably lugging the hell out of fourth spewing coal because I’ll drop out of my powerband.
my 7.3 Gets 20 to 22 if I keep it under two thousand rpm easy. Sometimes even more. I'm at almost 9000 pounds in this rig.
We are all moving at 1,000 mph as our we spin around in a circle. Of course that is not counting the speed that we move around our Sun or the speed our Sun moves around our Galaxy. We would all be dead if everything just stopped. You can really say that our speed keeps us alive and sudden stops can kill.
That is especially true when you team up sudden stops with driver distraction. When I drove commercial truck I once saw an accident because the driver a few cars in front of me had to look at a policeman giving out a citation to a car on the other side of the interstate. In turn that caused another accident because one of the cars in front of me could not stop and hit the car that was looking at the policeman in the other lane - fortunately I stopped before I hit somebody.
It has been 15 years since I retired from trucking. My State loves to slow down traffic for our work zones. Ohio had 60 or 65 mph speed zones (my memory might be a little foggy). But I witnessed far fewer accidents in the Ohio's work zones than I did in my home State PA. Sometimes we would turn two lanes of our Interstate highways into one lane 35 mph parking lots as we slowed down and held up traffic.
Ohio ran the lighter traffic on the apron and left the heavier traffic use the one lane that was still open. The reason they did that is because the shoulder of our roads does not have the same base. Ohio was not the only State that would run the lighter vehicles on the shoulders. Because they did not hold up traffic there were fewer accidents.
To create an accident all you need is one distracted driver and for traffic to slow down or stop - we never learned that lesson in PA. PA loves to slow us down in the work zones for worker safety. But if you look at the national statistics from the NHTSA you will see that only one in ten people that die in work zone accidents is a pedestrian; that means that nine out of ten people that die are motorist (us).
We can stop many of those accidents with better highway design and better layouts for our work zones and thus save many lives. Speed is not the enemy. Constant stopping and starting reduces our fuel economy and increases our greenhouse emissions.
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The Pantera with 351C was scary. Diapers not required, but highly recommended.
