warren@ihnss.UUCP (Warren Montgomery) (06/25/84)
I'm afraid I started this topic (again) unintentionally with a posting trying to make a point that the long term energy problem is real, in spite of our short term glut/crisis fluctuations. I didn't intend to start another 55mph discussion, but I will throw my 2 bits worth in on a couple of topics: "But my car gets better mileage at 70 than 55": As has been pointed out before, there is definitely more energy spent per mile in overcoming friction and drag at the higher speed, since both have components that grow faster than linearly with the speed of the car. Poor tuning or gear ratio selection can result in anomolous behavior, but I really doubt the claims that with a normal car and comparable driving you do better. Right after the 55mph limit was imposed, there was a real problem with trucks that had been designed with their top gear appropriate for travel at 70. The problem was not that the truck would not run more efficiently at a low speed if it could just run there, but 55 was near the shift point and more energy was wasted shifting back and forth than was saved by the lower drag at 55. "100 mpg carburetors": Yes, there are probably ways to improve the mileage of cars. Look at what has happened since '73 in the way of improved mileage. You can buy cars which claim to get well over 50mpg these days (though I don't know if they come through!). Anyone who believes that there is a technology for almost limitless gas mileage out there that is being surpressed by oil company greed is probably quoting the national enquirer as a source. "lower speed limits cause increased congestion": There is some truth in this. If you believe the old rule about 1 car length between cars for every 10 mph, then you will note that the total space required per car is equal to speed/10 + 1 car lengths. The space needed between the cars drops linearly with the speed limit, thus you would expect the net througput to remain the same, however the "overhead" of the space needed by the cars themselves is unchanged, leading to a somewhat lower highway capacity as the speed drops. (All wiped out I'm sure by other factors, like the change in car size). Having seen driving behavior in both the pre and post 55mph era (guess that dates me), and behavior in other countries, I have another theory about poor mileage and accidents as a result of a speed limit decrease: My guess is that each driver/car has a natural "terminal" velocity, one at which the pressure of foot on gas pedal is comfortable and the road noise and the scenery flying past is not too uncomfortable. On the autobahns and before the days of 55mph limits, the natural limit for most people was at or below the legal limit, thus people drove at a comfortable pace, driving alertly and at a consistent speed. 55 mph on a road designed for travel at 70 seems unnaturally slow to most drivers. This problem is made worse by the increasing use of streamlining and airconditioning, which decrease your sense of speed. Thus people are constantly in conflict, relaxing their vigilance and letting the spedometer creep towards 75, then realizing that they are suddenly passing a lot of other cars and slacking off (or even slamming on the brakes) before they get caught. I have seen many people who drove with gas and brakes in alternation at 55. This kind of oscillation probably hurts mileage and causes accidents. It certainly increases the perception of inefficiency and danger. Maybe we ought to be designing cars that make it more apparent how fast you are really going! -- Warren Montgomery ihnss!warren IH x2494
seifert@ihuxl.UUCP (D.A. Seifert) (06/26/84)
> "But my car gets better mileage at 70 than 55": As has been pointed > out before, there is definitely more energy spent per mile in > overcoming friction and drag at the higher speed, since both > have components that grow faster than linearly with the > speed of the car. Poor tuning or gear ratio selection can > result in anomolous behavior, but I really doubt the claims > that with a normal car and comparable driving you do better. > Right after the 55mph limit was imposed, there was a real > problem with trucks that had been designed with their top > gear appropriate for travel at 70. There is also the problem that some cars cannot cruise at 55 in top gear, either. This forces then to run in a lower gear and use more gas. How come your friendly neighborhood DC-10 doesn't have to go 55? I bet it would get better milage at a slower speed too. > Having seen driving behavior in both the pre and post 55mph era > (guess that dates me), and behavior in other countries, I have > another theory about poor mileage and accidents as a result of a > speed limit decrease: > > My guess is that each driver/car has a natural "terminal" > velocity, one at which the pressure of foot on gas pedal is > comfortable and the road noise and the scenery flying past > is not too uncomfortable. On the autobahns and before the > days of 55mph limits, the natural limit for most people was > at or below the legal limit, thus people drove at a > comfortable pace, driving alertly and at a consistent speed. > > 55 mph on a road designed for travel at 70 seems unnaturally > slow to most drivers. This problem is made worse by the > increasing use of streamlining and airconditioning, which > decrease your sense of speed. Thus people are constantly in > conflict, relaxing their vigilance and letting the > spedometer creep towards 75, then realizing that they are > suddenly passing a lot of other cars and slacking off (or > even slamming on the brakes) before they get caught. I have > seen many people who drove with gas and brakes in > alternation at 55. This kind of oscillation probably hurts > mileage and causes accidents. It certainly increases the > perception of inefficiency and danger. Maybe we ought to be > designing cars that make it more apparent how fast you are > really going! Going 55 on a road good for 70 (or 90, or whatever) not only *seems* too slow, it IS too slow. Safe driving demands proper concentration. put-puting along at 55 on a typical interstate is very dangerous. If you're looking for wind-in-your-face, convertibles are coming back, and I think you can still fold down the windshield on a Jeep. (though I'm not sure if it's legal to on the road) There's always motorcycles. I'll stick with a 'streamlined' car with air. Gets better mileage that way. (air uses less gas than the aero loss from open windows or roof) Safer too, there's a *reason* Jeeps come with roll-bars. -- _____ /_____\ Hey, Woodstock, have you seen my sunscreen? /_______\ |___| Snoopy ____|___|_____ ihnp4!ihuxl!seifert