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Daydreaming of an American "Autobahn"

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Re: Daydreaming of an American "Autobahn"
Post by Odium   » Wed Jun 14, 2017 11:52 am

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I can't imagine any politician being so stupid, and I have a pretty low opinion of politicians intelligence. A quick google search gave me the figures of around 1.4 million Americans with a net worth of over 5 million, which I imagine would be a baseline to even begin to afford the kind of user fees you are talking about. I rather doubt even 10% would want to spend that kind of money, so you are talking about using billions or trillions of tax dollars and appropriating thousands of people's land (sometimes in their families for generations) simply to build a monument to the vanity of less than 140,000 people, who can easily pay for their own entertainment. While politicians often en do monumentally stupid things to make their buddy's a few more bucks, the public rage this would spawn would be unbelievable.
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Re: Daydreaming of an American "Autobahn"
Post by Jonathan_S   » Wed Jun 14, 2017 3:53 pm

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munroburton wrote:Not even the Veyron can get you that far past the 250mph barrier. Plus you have fuel range issues with cars, especially high-speed performance cars with smaller tanks to reduce weight. You'd need to make sure your route has gas stations every ~75 miles and would be making two or three fuel stops per hour. Tyres would probably need to be replaced multiple times too.

Pit stops do kill your average speed. It'd be an interesting academic exercise to get some data on fuel consumption, on cruise control, at various high speed and figure out the most efficient cruising speed for long distance travel. You'd be trading off higher peak speed against fewer fuel stops at lower speeds.

Trickier would be optimum speed for a given trip, since you'd ideally be targeting whatever speeds resulted in your arriving with a nearly empty tank.

Lets say you had a car that was good for 300 miles at 55 mph; that'd take 5.4 hours to drive.

Now, using made up fuel efficiency numbers, if we assume the range dropped in half at 100 mph (unlikely to be that big a drop) you'd need a gas stop, but (ignoring the stop) you'd save 1.4 hours -- more than enough to slow down, get gas, and get back on the road to beat your original ETA.

But if the range drops in half again at 115 mph you're now saving 24 more minutes at the expense of 2 more gas stops. That's much closer to break-even; and going even faster than that would be counter productive -- you'd spend more time stopping for gas than you'd save by the higher speed.

Also, I'm ignoring that accelerating to cruising speed takes significantly more fuel than maintaining that speed, so the more stops you add the more you have to stop due to fuel burn resuming your speed.


But like I said, it would be interesting to get fuel efficiency speed curves for various cars and plot the optimal long distance cruise speed. (Though it'd be significantly affected by your assumptions on how big an average delay a fuel stop is)
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Re: Daydreaming of an American "Autobahn"
Post by munroburton   » Wed Jun 14, 2017 4:54 pm

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Jonathan_S wrote:
munroburton wrote:Not even the Veyron can get you that far past the 250mph barrier. Plus you have fuel range issues with cars, especially high-speed performance cars with smaller tanks to reduce weight. You'd need to make sure your route has gas stations every ~75 miles and would be making two or three fuel stops per hour. Tyres would probably need to be replaced multiple times too.

Pit stops do kill your average speed. It'd be an interesting academic exercise to get some data on fuel consumption, on cruise control, at various high speed and figure out the most efficient cruising speed for long distance travel. You'd be trading off higher peak speed against fewer fuel stops at lower speeds.

Trickier would be optimum speed for a given trip, since you'd ideally be targeting whatever speeds resulted in your arriving with a nearly empty tank.

Lets say you had a car that was good for 300 miles at 55 mph; that'd take 5.4 hours to drive.

Now, using made up fuel efficiency numbers, if we assume the range dropped in half at 100 mph (unlikely to be that big a drop) you'd need a gas stop, but (ignoring the stop) you'd save 1.4 hours -- more than enough to slow down, get gas, and get back on the road to beat your original ETA.

But if the range drops in half again at 115 mph you're now saving 24 more minutes at the expense of 2 more gas stops. That's much closer to break-even; and going even faster than that would be counter productive -- you'd spend more time stopping for gas than you'd save by the higher speed.

Also, I'm ignoring that accelerating to cruising speed takes significantly more fuel than maintaining that speed, so the more stops you add the more you have to stop due to fuel burn resuming your speed.


But like I said, it would be interesting to get fuel efficiency speed curves for various cars and plot the optimal long distance cruise speed. (Though it'd be significantly affected by your assumptions on how big an average delay a fuel stop is)


The drop in range should drop more than half. Aerodynamic drag increase is exponential to speed, though of course there are many variables involved.

There are some curves mapped out for various vehicles.
http://www.greencarcongress.com/2006/05 ... mptio.html
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Re: Daydreaming of an American "Autobahn"
Post by Annachie   » Wed Jun 14, 2017 5:28 pm

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Topgear, the UK show not the US one, actually discussed that range problem in a couple of their "races".
If I remember it right, one car was 17 minutes of fuel at full speed.

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Re: Daydreaming of an American "Autobahn"
Post by Jonathan_S   » Thu Jun 15, 2017 12:31 pm

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munroburton wrote:The drop in range should drop more than half. Aerodynamic drag increase is exponential to speed, though of course there are many variables involved.

There are some curves mapped out for various vehicles.
http://www.greencarcongress.com/2006/05 ... mptio.html

Thanks for that link. Though from 55 mph to 100 mph it looks like only one car might have dropped 50% in mpg (looking at the 8 cars in mpg chart) - the Opel looks to have been about 45 mpg at 55 mph, and at 100 mph it's down to the low to mid 20s. Getting a 50% drop (relative to 55 mph) seem to require getting up to more like 110. But past 'normal' highway speed the exponential drag does start taking a major toll.

Annachie wrote:Topgear, the UK show not the US one, actually discussed that range problem in a couple of their "races".
If I remember it right, one car was 17 minutes of fuel at full speed.

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IIRC that was the Bugatti Veyron. A quick google seems to confirm, showing people saying at top speed it'll drain its tank in 12 minutes (which is apparently good because it's tires are only rated for 15 minutes at its top speed :shock:)
[Mind you it's a damn fast 50 miles if you've got that long a straightaway]
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Re: Daydreaming of an American "Autobahn"
Post by aairfccha   » Fri Jun 16, 2017 2:44 pm

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munroburton wrote:So wasteful. So inefficient.

Why not get behind high-speed trains? A coast-to-coast mag-lev would allow safe, comfortable and very quick travel.


... which would require a very expensive transcontinental track which is entirely incompatible with existing ones while competing with the even faster planes which only need infrastructure at the end points of travel. There are a few corridors with the population density to make (conventional) high speed trains work, but short of radical changes (like a massive increase in Amtrak funding or flying becoming much more expensive) I don't really see the potential for transcontinental high speed rail, maglev or conventional.
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Re: Daydreaming of an American "Autobahn"
Post by Bruno Behrends   » Sat Jun 17, 2017 3:11 am

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I maybe should add some facts:

- around 50% of the Autobahnen do have explicit speed limits (usually due to heavy traffic or construction constraints)

- even in places with no explicit speed limit paragraph 1 of the German road traffic code states that drivers have to show considerateness at all times - meaning for instance that speed always has to be adapted so that driving is safe, (even in places where no explicit speed limit exists.)

- at all times (meaning even or especially where no explicit speed limit is set up) one is required to keep the safe distance to the front traffic (so that one can always safely stop in case of something untoward happeing in front).
In case of a car going 300 km/h (like an Aston Martin at top speed) that distance would be quite long and hardly achievable in any but the most empty of traffic situations. (Simple reaction time at 300 km/h means you travel 90 meters before even beginning to brake. So any obstacle appearing at 90 m distance ahead you impact in at full speed without having time to even think about braking.
On a usual day with even an only moderatly travelled Autobahn going at that speed would be extremely dangerous and probably draw a police reaction if maintained for a longer period of time.

- road racing is illegal under any circumstances (speed limit or no). British Ferrari drivers racing each other on the Autobahn have been stopped by police and had their cars confiscated.

- in practice (on a good day with moderate traffic) the right lane (due to all the truck traffic there) usually goes around 90 km/h, the center traffic lane maintains between 140 km/h and 160 km/h (but has frequently to slow down to below 100 km/h due to passing trucks switching to the center line. The left line does have occasional cars going as fast as 200 km/h (or sometimes more than that). But they have to brake very frequently indeed (because passing trucks switching from the right lane to the center line push the passenger cars that go there with 140-160 over to the left lane (and usually cause a congestion which slows them down to 100-120 first.) So the left lane traffic has to be very alert and frequently slow down to 120 or less. And always keep in mind that this can potentially happen whenever there is any traffic ahead. So the 300 would be practically impossible to maintain.
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