Path: utzoo!mnetor!motto!ecijmm!jmm From: jmm@ecijmm.UUCP Newsgroups: ont.general Subject: Re: Highway Driving Rules Summary: but not much: speed limits = wasted gas, wasted time Message-ID: <278@ecijmm.UUCP> Date: 6 May 89 04:07:14 GMT References: <89Apr26.134028edt.9320@ois.db.toronto.edu> <440@bnr-fos.UUCP> <1989Apr27.112604.11727@gpu.utcs.utoronto.ca> <1730@yunexus.UUCP> <3166@looking.UUCP> <9522@watcgl.waterloo.edu> <1693@dciem.dciem.dnd.ca> Reply-To: jmm@ecijmm.UUCP (John Macdonald) Distribution: ont Organization: R. H. Lathwell Associates, Elegant Communications, Inc. Lines: 59 Keywords: In article <1693@dciem.dciem.dnd.ca> tim@dretor.dciem.dnd.ca (Tim Pointing) writes: >In article <9522@watcgl.waterloo.edu> kim@watsup.waterloo.edu (Kim Nguyen) writes: >>In article <3166@looking.UUCP> brad@looking.UUCP (Brad Templeton) writes: >>>I believe that somebody >>>once calculated that when the US reduced from 70 to 55, thus making >>>everybody's trips take 25% longer, you actually got a bad result. >> >>Then, the gasoline consumption argument for lowered speed limits is >>silly too, since you WASTE 25% more gas just running your car for 25% >>longer getting there... > >Alas, this argument falls down when you look at the math of the situation. >The cars mileage (kilometreage?) goes up as you slow down from 70 to 55. >Since the distance you are travelling has not changed, you will will >actually use less gas running your car for longer. > > distance / mileage(mpg) = gas_used > > CONST / INCR => DECR > Many years ago, I used to weekly travel between Waterloo and Toronto. I took advantage of this to test the validity of the above formula. On different trips, I did my best to maintain a constant speed througout. At higher speed, this was possible, but presumably the improved mileage while I was forced to lower speeds was somewhat balanced by the reduced mileage while I was accellerating back up to the desired speed. Anyway, the results I ended up with (from memory and they were somewhat rough at the time - this is not a true scientific measurement) were: Speed Mileage Comment (mph) (mpg) I use metric now, but this was looong ago. 95 24 I was young and foolish then. 85 26 75 26 65 25 55 24 It was hard to maintain a speed this slow (limit - 15). My conclusion at the time was that the folk knowledge that high speed means drastically lower gas mileage was not true for me. My car at the time was a 5-speed manual, 2 litre, smallish car (Toyota Corona). This was in the days of the large automatic-transmission American battlestar. I concluded that for such cars it could quite likely be true that they had a similar looking mileage curve except the peak was at 55 mph instead of at 80 mph as seemed to be the case for my car, and that by 70 mph they could be falling off fast. This made it particularily annoying to me when a few years later, the speed limits were dropped from 70 to 60 "to save gas". The saving in gas from reducing speed limits, was soon overwhelmed by the much greater saving in gas from the great downward shift in average car size. If the change in car size had come first, the reduction in speed limit would have had almost no effect in gas usage. (Of course, without the general conscience having been pricked by the official concern expressed by the drop in speed limit, the car style transition might have been dramatically less marked.) -- John Macdonald