The court long ago held that once a person is arrested they are subject to being searched. If their car is within finding distance, it too can be searched. This Court ruled in 2001 that a person could be arrested for violating virtually any traffic law, including the failure to wear a seatbelt. And, once arrested you have no fourth amendment protections.
For all practical purposes, this gives the police the power to stop, arrest, and search anyone they feel like “checking out” or harassing. Arabs might be the flavor of the day on Monday, Tuesday it’s blacks in luxury cars and on Wednesday it’s young men driving sport compacts.
The options/excuses for a stop are endless; burned out bulbs, unused seatbelts, (real or imagined) failure to properly signal, touching the center line, hitting the shoulder, two MPH over the speed limit, driving too slow, rolling a stop sign, rolling a right on red, failure to yield to a pedestrian, or talking on a cell phone (inattentive driving).
If the police want to stop you, they can. If they want to arrest you, they can. If they want to search you and your vehicle and your passengers, they can.