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Recently, ActionLab has posted this video https://www.youtube.com/watch?v=W8Oc3Etev34&t=1s, titled "Do Traffic Turbines Actually Work". It has caused a heated debate, as people discussed whether it is implementable. But here, I want to discuss its actual physics principles first.

For clarity, let's define the traffic turbines "work" if it manages to save energy (everyone knows it could generate electricity). Also assume that the road is flat, and ignore the case where the cars are braking.

To commence with, the electrical energy generated by the turbines comes from the kinetic energy of the wind, which in turn comes from the kinetic energy of the cars. Hence, obviously the air resistance experienced by the cars will increase. It means that the cars would have to burn more fuel in order to "compensate" that extra air resistance. My question is, in this case does the extra electrical energy just comes from the chemical energy, i.e. burning the fuels? Therefore, is there actually any energy that is being saved?

(This question is originally asked in physics stack exchange but is redirected here)

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    $\begingroup$ Would you drive a car that is breaking? $\endgroup$
    – Solar Mike
    May 27, 2023 at 8:07
  • $\begingroup$ Closed on the Physics Stack: physics.stackexchange.com/q/765641 $\endgroup$
    – Solar Mike
    May 27, 2023 at 11:21
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    $\begingroup$ edited for correct context, breaking versus braking $\endgroup$
    – fred_dot_u
    May 27, 2023 at 15:19

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I think that this idea will not result in an overall improvement in energy efficiency of human civilization.

  1. I have personally experienced, walking across and near a large road, that there is a wind which consistently follows the direction of traffic, persisting even when a car has not passed for many seconds. I believe it is a reasonable assumption that cars will often experience this wind as an overall reduction in their relative wind and therefore drag.

  2. If these turbines successfully extract energy from this road wind, then they must be decreasing the wind compared to if they were not present, thus increasing vehicles' drag, thus increasing fuel consumption.

  3. But is it still possible we are saving energy overall? Is it possible that the additional energy consumption is outweighed by the electricity generated?

    • For gasoline cars: No, because if it were, then we could surely do even better by building power plants that burned the same additional amount of gasoline and skipped the part with the moving cars. We do have gasoline power plants: we call them portable generators. Most are smaller than car engines, but even large ones are only used for emergency backup and off-grid applications. Bigger, stationary engines are more efficient than lots of smaller ones.

    • For electric cars: No, because you're going from electricity to electricity, while also having all of the losses from battery charging and turbulence. There's just no way to win.


Here are a couple of ways I can think of that these turbines might be useful for reasons other than net energy efficency:

  • If calming the wind specifically had some kind of benefit to the traffic, such as reducing buffeting that could cause loss of control, and extracting the energy is more effective, cheaper, or more aesthetic than building walls. (This seems unlikely but possible.)

  • Energy harvesting devices of any kind may be useful to provide small amounts of power to remote equipment, rather than having to bring power lines to them. However, in outdoor environments solar panels are a cheap and low-maintenance solution, and in tunnels there are generally wires run anyway for lighting (which, for safety, must always operate even if there is no traffic).

  • They could look really cool.

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You will burn more fuel than what you generate.

Based on the first law: energy can be converted form one form to another,

and the second: you won't get all of it.

AKA as perpetual motion is a myth.

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    $\begingroup$ Is this correct? Are the turbines not so far away that they're only capturing energy from the air turbulance that would otherwise be dissipated more gradually? How would that increase drag on the car? $\endgroup$
    – Transistor
    May 27, 2023 at 10:21

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