Comments on: and then the clouds parted http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/ Getting around the Bay Area with Denis Cuff and the Queen of the Road Tue, 17 May 2011 06:04:22 +0000 hourly 1 http://wordpress.org/?v=3.5.1 By: Bruce De Benedictis http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/comment-page-1/#comment-1847 Bruce De Benedictis Thu, 10 May 2007 17:19:16 +0000 http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/#comment-1847 The chart on the page South Bay Resident cited says pretty much what I said: There is not much difference in fuel mileage from 25 mph to 55 mph. Whether it amounts to anything is not really clear. Car manufacturers would do well to make the point where the big bend in the curve come sooner and sooner.

Of course, the real question is not automobile mileage, but truck mileage. That is what people worry about in West Oakland. All the sources say that diesel trucks get about 4 mile per gallon, except for CARB diesels, which get about twice that, without regard to speed. You get those figures for transit buses as well as trucks, so speed is clearly not much of a factor. The upshot is that there will not be much difference in pollution.

]]> By: South Bay Resident http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/comment-page-1/#comment-1846 South Bay Resident Fri, 04 May 2007 05:13:28 +0000 http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/#comment-1846 Bruce:

You missed half of what I was saying. To run a gasoline engine at its optimum efficiency, you usually need to be pretty near peak output with the throttle pretty far open. A gasoline engine running with a nearly closed throttle is really inefficient. This offsets many of the gains you get from driving at a lower speed. At 15 miles per hour rolling resistance (which doesn’t vary much with speed) is more important than air drag for most cars. While there are vehicles that have optimum fuel economies at speeds that low you’re just wrong about typical cars.

Here’s a link to a US Government site on fuel economy that contains a chart of fuel consumption vs. speed which is typical of gasoline-engined cars (the charts for diesels and hybrids look different).
http://fueleconomy.gov/feg/driveHabits.shtml

]]> By: Capricious Commuter http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/comment-page-1/#comment-1844 Capricious Commuter Fri, 04 May 2007 00:22:09 +0000 http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/#comment-1844 Bruce, please try to keep the criticism to the stats. I can think of very few instances where describing a person commenting in negative terms is appropriate here. As for the information proffered, you can attack all you want. That’s what the blog’s all about.

]]> By: Bruce De Benedictis http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/comment-page-1/#comment-1845 Bruce De Benedictis Thu, 03 May 2007 23:32:57 +0000 http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/#comment-1845 The speed of a vehicle’s engine depends on the gearing, not the speed the vehicle is traveling at. I suspect that peak mileage under constant running conditions is probably about 5-15 MPH, but that may be high. Shell Oil, initial sponsors of the gasoline mileage contests, said in their advertisements years ago that if you are about to run out of gas, you should reduce speed. I would tend to believe them rather than someone who has a history of citing unlikely statistics

]]> By: South Bay Resident http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/comment-page-1/#comment-1843 South Bay Resident Thu, 03 May 2007 16:16:37 +0000 http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/#comment-1843 The peak fuel economy of most cars using normal driving techniques* is around 50-60 MPH. At higher speeds, the amount of energy needed to overcome wind resistance increases dramatically. At lower speeds the car’s engine isn’t running near its peak efficiency. As a side note, there’s nothing magic about 50-60 MPH it just happens to be the speed that most cars are designed for; some cars, such as hybrids, are more efficient at lower speeds. The real killer about diverting traffic to city streets is that the traffic has to stop and speed up again. This wastes lots of fuel compared to cruising at a constant speed.

*Odd driving techniques, such as running the engine at around 3/4 throttle near the peak of its torque band to accelerate from 15-30 miles per hour then coasting back down to 15 with the engine turned off can get your very good fuel economy (like 3 x the EPA highway rating), but it’s not good for the car and annoying as heck to those around you.

]]> By: MikeyP http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/comment-page-1/#comment-1841 MikeyP Thu, 03 May 2007 05:35:47 +0000 http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/#comment-1841 FWIW, afternoon rush hour traffic on Jackson street through Hayward (from 880/92 to Mission) has been unusually heavy all week. I have no idea if this is simply coincidence or if this is due to 580 avoidance.

]]> By: Bruce De Benedictis http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/comment-page-1/#comment-1842 Bruce De Benedictis Thu, 03 May 2007 04:39:25 +0000 http://www.ibabuzz.com/transportation/2007/05/02/and-then-the-clouds-parted/#comment-1842 You know, I wonder what the emission impact actually is. The slower a vehicle travels, the less fuel it uses, so the fewer emissions are produced. The only way emissions will be increased is when the traffic is stopped, and if the fuel usage is reduced enough, that will diminish the effect of stoppages, which happen often enough in heavy traffic even when everything is normal!

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