You’ve felt it before: a large vehicle passes you, and your vehicle moves or shakes a little. If the windows are down it might blow your hat off your head or your hair into your eyes.
Any vehicle in motion pushes air out of its way- a car less so, because it’s more aerodynamic (and one reason why wedge-shaped sports cars can go faster with less effort, and why fuel-efficient cars look funny!) A flat-front Mack truck pushes a tremendous amount of air out of the way. Much like a subway train pushing air through the station, vehicles do the same thing. There’s just more outward space for the air to go. One of those spaces is to the side of the vehicle.
Imagine you’re in a 3000 lb vehicle. That airflow is going to have minimal effect. But to a bicyclist, this has the ability to push us a few inches, or maybe even a foot to the side. In some cases it’s not a surprise, but many times it will catch us unaware, and we have to steer slightly to correct our travel path. Sometimes it causes an overcorrection, and we may move as much as a foot or even two feet into the travel lane.
Very large vehicles such as tractor-trailers or dump trucks (especially those with open space underneath) have another effect: there’s a slight vacuum in the air it pulls with it. This has the effect of pulling a bicyclist into the side of the vehicle as it passes.
These are reasons we need substantial separation from all vehicles to prevent the turbulence from affecting our travel path.
Helping educate the motorized vehicle user (and possibly some bicyclists) regarding bicycles, bicycle use, bicycle laws, and the nuances of bicycle use on public roadways.
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