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Highway Tailwind

Canvas tunnels built over highways channel an artificial tailwind
 
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Over long, straight stretches of busy highways, construct heavy canvas coverings so that there is a tunnel for each direction. Periodically throughout the tunnel, place large fans that blow the air in the direction of the traffic. The strong tailwind in the tunnel reduces drag on the vehicles, which is prominent at highway speeds, resulting in higher fuel economy.
Cuit_au_Four, Apr 14 2012

Covered_20Highway_20Wind_20Tunnel [spidermother, Apr 17 2012]

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       Traffic would have to be pretty packed to balance out the drag on the canvas and road.
FlyingToaster, Apr 14 2012
  

       Why only long straight stretches?   

       I'd say just skip the fans. You don't want the air going faster than the cars. There will be losses to friction with the canvans and road as well as with the moving cars. The most efficient speed for the air would be some fraction of the traffic speed. When there are no cars present, the ideal speed it 0. When there is one car avery 20 seconds, the ideal speed is probably just a little over 0. If the traffic is bumper to bumper moving at 60 mph, you probably want the air moving pretty close to 60 mph depending on how smooth the walls are. Luckily, the more traffic there is, the faster the air will move without any fans needed.   

       Someone could study this in an exsisting tunnel to see what wind speed develops and what efficiency gain is experienced by vehicles, but I'd have a hard time imagining that it would be worth the cost of constructing the tunnel. Using canvas might be cheaper to start with, but with the upkeep and replacement I doubt it would be very cost effective. A transparent roof/walls would be nice to avoid the need for lighting during the day, but would need more frequent cleaning. A concrete tunnel would be nice to contain the noise and reduce maintenance, but costs more and makes expanding the road even harder.
scad mientist, Apr 17 2012
  

       Part of the appeal of driving on highways (as opposed to sitting in an aisle seat on a plane) is the view. Take away that view and you take away a motorist's love of the open road. As an avid road warrior, I feel obliged to fishbone this idea. Let's focus on making the vehicles more fuel efficient. To each his own (to each driver his own choice of balance between power and fuel economy, that is).
21 Quest, Apr 17 2012
  

       //long, straight stretches// where you can watch your oximeter numbers drop, feel your fingers start to tingle, see your peripheral vision fade - any moment now, you're going to collide with the growing traffic-heap - hopefully, it's torn through the walls...
lurch, Apr 17 2012
  

       That's a good point; in addition to starving drivers of oxygen, it will also starve engines of same, decreasing fuel efficiency.   

       I was going to point out that this idea assumes the existence of 'canvas' possessing a heretofore unknown degree of long-term durability, but the longer I linger, the more things that are just fundamentally wrong with this idea become evident. Please try again.
Alterother, Apr 17 2012
  

       You could achieve the same improvements in gas mileage much cheaper by just making more aerodynamic cars.
DIYMatt, Apr 17 2012
  

       I wondered a few times while driving through long tunnels in Europe (St Gotthard 16km; Frejus 12km; Laerdal 24km) whether the oxygen levels were retarding fuel economy. It makes sense to reduce oxygen levels a little, to reduce the risk of fire in a tunnel.
UnaBubba, Apr 17 2012
  

       Lower o2 should help gas mileage, the same way a hot day helps gas mileage. Less o2 = less fuel required to maintain proper mixture, but reduces power.
DIYMatt, Apr 17 2012
  

       Not that I can back this up with quantifiables, but opportunities for both fuel economy thru aerodynamics and fire danger reduction are probably quite limited.   

       Okay, contrary viewpoint expressed, going to bed now.
normzone, Apr 17 2012
  

       Cars that are overpowered and have a throttle (which is still most of them) could possibly benefit from reduced pumping losses, as the throttle would be opener. Possibly. And each car + driver wiped out represents a *huge* fuel saving.   

       Why has this not been [MFD]? I thought artificial tailwind assistance had been done a few times already here.
spidermother, Apr 17 2012
  

       It has. It seems to be one of those dead horses that still gives an occasional twitch.
Alterother, Apr 18 2012
  
      
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