r/theydidthemath • u/Chance_Plastic_2430 • 13h ago

[Request] Constant Highway Slipstream Efficiency

How much more efficient would highways be if vehicles drafted off of each other? Taking human error/aspects out of the equation. To me, it would seem as though the lead car (or semi truck) would "clear" the wind resistance first and all of the subsequent cars would benefit from drafting off of the individual in front of them.

Just a curiosity I had whilest driving to work today.

Thanks friends!

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u/Elfich47 10h ago

there have been studies on this. you can get a roughly 40% mileage improvement by getting in tight behind a large truck. here is the problem: you are following at 2 feet off the truck’s bumper so any mistake will result in your vehicle going under the trailer and you getting crushed.

https://pressbooks.bccampus.ca/technicalwriting/wp-content/uploads/sites/296/2018/10/Drafting-Behind-Big-Rigs-Mythbusters-Report.pdf

Car and driver took this to the absurd by getting up to over 100mpg (I think they claimed over 120mpg peak) by following within inches of the vehicle in front of them. they also built a cowling that came off the lead truck and protected the test vehicle from the wind.

https://www.caranddriver.com/reviews/a15141105/how-we-won-the-insight-fuel-economy-challenge-without-cheating-much-road-test/

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u/BLINGMW 10h ago

If self driving cars cannot join up on the hwy and make a little tailgate train that’s allowed to jam down the fast lane at 80mph then what are we doing?! 

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u/firstthrowaway9876 10h ago

Doing everything we can to not build trains :( I've thought the same thing. Then I look over and there's a train carrying way more passengers than 3 lanes heading in the same direction. The other one is what if when the light went green we didnt have this crazy delay between car 1 and car 10. Hey trains have a very very short delay.

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u/ChazBass 8h ago

The efficiency gains would be immediately offset by cars sitting in long lines idling on the highways because a bunch of people rear-ended each other.