Final answer:
The funneling air between two semi-trucks driving side by side leads to decreased air resistance and possibly increased fuel efficiency, due to principles of aerodynamics and Bernoulli's effect.
Step-by-step explanation:
When two semi-trucks are driving next to each other on the highway with their sides causing the air to funnel between them, the effect is that the air resistance between the trucks is decreased. This is based on the principle of aerodynamics, similar to how car designers aim to shape vehicles to reduce air drag. According to Bernoulli's principle, as the air speed increases between the trucks, the air pressure decreases. This lower pressure differential can result in the trucks being pulled slightly together and can potentially lead to increased fuel efficiency because there is less air resistance to overcome.