Aerodynamic Buffeting of Adjacent Vehicles

"Air turbulence around trucks does not increase if they are longer or heavier than currently used trucks. However, the gap between the tractor and the semitrailer it tows can be the source of a transient disturbance to adjacent vehicles, if they are operating in substantial crosswinds. Doubles combinations have two of these gaps, while triples have three. Thus, a passing car could experience this transient disturbance that many more times under these conditions. To the extent that motorists now find these occurrences disconcerting, they would experience that feeling incrementally more often if multiple trailer combinations were more widely used . . ."

"When traveling at high speeds next to a truck, your vehicle may be pulled closer to the truck because of the air movement . . ."

"Common unsafe acts committed by car drivers in the vicinity of large trucks: Passing a truck, then being blown out of position by air turbulence or cross-wind . . ."

"When approaching a large vehicle, keep a steady grip on your steering wheel. Larger vehicles create more air turbulence at highway speeds . . ."

"Highway support structures such as signals and luminaries are also subjected to wind effects, in particular the action of fatigue. Since the wind-induced fatigue failure of highway support structures is a rare, but quite dangerous phenomenon, a research program is underway to develop methods of predicting the fatigue response of these structures. The main issue of concern is how to model the effects of vortex-shedding, wind gusting, and truck turbulence on the fatigue life of support structures so that more reliable structures can be built . . ."

'Comparing the laminar and turbulent airflow around a car and a truck.'

Riding in gusting crosswinds . . .​

 

They say it's especially noticeable in crosswinds. Like a venturi effect, methinks.

"In fluid dynamics, an incompressible fluid's velocity must increase as it passes through a constriction in accord with the principle of mass continuity , while its static pressure must decrease in accord with the principle of conservation of mechanical energy. . ."

Fluid dynamics are involved in the study of truck aerodynamics, as well.

I've seen a venturi valve used as a kind of 'turbo' compressed air nozzle, that is. It could be that with uncompressed air, the drop in pressure sucks adjacent vehicles into the gap (or there's both a push and pull to the turbulence).

Anyway, they list something like that as an example of Venturi effects: "Large cities where wind is forced between buildings - the gap between the Twin Towers of the original World Trade Center was an extreme example of the phenomenon, which made the ground level plaza notoriously windswept. In fact, some gusts were so high that pedestrian travel had to be aided by ropes . . ."

It's also called a gap wind.

"In some introductory textbooks and in the 'common knowledge' of many meteorologists, gap winds are explained by the 'funnel' or 'venturi' effect, in which the strongest winds occur in constrictions. Although funnel effects can influence wind speed, the strongest winds are generally not in the narrowest portion of gaps but rather in gap exit regions. Furthermore, other mechanisms appear to be far more important in modulating wind speed in and near gaps. The 'Funnel' or 'Venturi' Effect: Only a Part of the Story... Although the venturi effect is often not the dominant mechanism for large gaps (tens or hundreds of km long and several km wide), it can be very important for small scale gaps (on the order of a few km or less in length) where the contributions of the larger scale pressure gradients or changes in the height of near-surface cold air are less important . . ."

 

Some passenger vehicles have "Crosswind Stabilization"...

 

Height - and Heightened Safety Considerations
​

• Smaller vehicles can be pushed or pulled under a commercial vehicle with high ground clearance.
• Large vehicles generate wind gusts that can push smaller vehicles into other lanes.
• Tall vehicles have a higher center of gravity, roll over more easily than smaller vehicles and must go much slower on curves and ramps.

Trucks roll over more easily in high winds. Rolling between two trucks could be more risky too.

 

In slipsreaming, some wake effects may be caused by a turbulent downstream (like a katabatic wind) of a solid body. Like a tailwind too, a reverse flow may be caused by a blunt body (which sucks toward the back of the object). These effects could pertain to a moving truck, like how parachutes seem to spin in a vortex behind dragsters (I would guess—well, maybe this would explain why highly maneuverable motorcycles sometimes run into the back of trucks, for no apparent reason).

"This phenomenon is often observed in wind tunnel testing of aircraft, and is especially important when parachute systems are involved, because unless the parachute lines extend the canopy beyond the reverse flow region, the chute can fail to inflate and thus collapse."

If the forces on a moving object change, that changes its speed or direction (or both).​

Anyway, it's safer for vehicles not to fly up behind trailers before passing, in general; the wake (or Magnus) effects could interfere with the last second timing of it (or at least a sudden tailwind would).

The wake is visible in snow (unless it blinds you, like that car behind it).​

 

Motorcyclist suffers life-threatening injuries...
"A motorcyclist was merging onto Hwy 77 from Hwy 33 when a strong gust of wind, which was partially caused by a semi-truck in the passing lane, caused him to lose control."

The National Highway Traffic Safety Administration also lists "Wind From Passing Truck" as a driver related factor of Fatal Two-Vehicle Motorcycle Crashes, meaning a passenger vehicle may have swerved into a motorcycle, after it was blown out of position by a truck. Or the motorcycle ran into a passenger vehicle, after a truck blew it out of position (they seem to use "driver related" in reference to either passenger vehicle drivers or motorcycle operators in Table 22 there).