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Originally Posted by Jt martin
In some spots on the Highway, you often can drive beside concrete walls. Is it adventitious to drive near these concrete walls in order to reduce aerodynamic drag?
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It's quite complicated and contradictory.
You get a partial tunnel effect, which is not good for fuel economy due to the negative effect of having walls in the proximity of your more-or-less streamlined shape / car - works a bit like the road.
But then, just about any cyclist will tell you pedalling in tunnels is a joy - as long as the tunnel isn't going uphill steeply
- so, what's up ?
The benefit of a tunnel, is that it eliminates all sidewinds, and in my experience, even a "partial tunnel" will reduce sidewind effects if you hug the leeward side of a barrier in heavy winds.
A tunnel with 1-directional traffic will have a traffic-wise airflow, which helps your FE.
But with 2 directional traffic, you bounce into the opposing traffic's pressure wave, which is bad. Ask any biker, sometimes it almost feels as if you're slamming into something when meeting a truck.
If the barrier separates the traffic directions, outside a tunnel, you may get the benefit that it also separates or reduces the opposing pressure waves.
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As a second question, is it adventitious to drive beside a larger vehicle? I know that if you have a crosswind, using a larger vehicle can help reduce the negative effects of that crosswind. With this not being a factor, does driving beside a larger vehicle give you an advantage?
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In my experience, it depends on your position alongside.
Coming out of a semi's wake, my fuel economy goes down first, then improves again as I pass alongside, only to become worse again as I get near the truck's front. (all on CC of course)
Staying put alongside semis isn't going to make you many friends on the road though
These effects are only seen on the instant fuel consumption display.