The Effects of Speed

A fast-moving vehicle is harder to hit than a stationary one-but it's also harder to control, and to attack from.
As shown on Table: Vehicle Speeds and Modifiers, when a vehicle travels at street speed or faster, it gains a bonus to Defense. However, that speed brings along with it a penalty on all skill checks and attack rolls made by characters aboard the vehicle-including Drive checks to control the vehicle and attacks made from it.