DANGER of sideswiping because of a decrease in air pressure in the space between them. Concept-The pressure drop between the area of two cars is based on Bernoulli's Principle of fluid mechanics.This inverse relationship between the pressure and speed at a point in a fluid is called Bernoulli's principle. Explanation- As the pressure between two cars drops suddenly, they are forced to move towards the lower pressure area by the outside pressure. Hence the danger of sideswiping enhances. As shown in the above diagram, when air passes through two cars, the velocity of air between two cars INCREASES which lead to a decrease in pressure of that narrow area. And in the outer area, the velocity of WIND is relatively low and pressure is relatively HIGHER and this leads to the pushing of two cars toward each other. Hence (Po > P1 and V1 < v2).