What is the test for a police officer to stop a vehicle for questioning under the Fourth Amendment?

The Fourth Amendment prohibits an officer from stopping a vehicle without founded suspicion of criminal conduct at the time of the stop. United States v. Salinas, 940 F.2d 392, 394 (9th Cir.1991). In order to justify a stop, officers must be "aware of specific, articulable facts, together with rational inferences from them, [which] reasonably warrant a suspicion that the person to be detained has committed or is about to commit a crime." Salinas, 940 F.2d at 394. We must consider the totality of the circumstances to determine whether founded suspicion exists. United States v. Sokolow, 490 U.S. 1, 8 (1989); Salinas, 940 F.2d at 394. Although we must consider the experience of a trained officer, such experience "may not be used to give the officers unbridled discretion in making a stop." Hernandez, 891 F.2d at 1416. Where the circumstances "describe a very large category of presumably innocent travellers who would be subject to virtually random seizures," an investigatory stop is not justified. Reid v. Georgia, 448 U.S. 438, 441 (1980) (per curiam ).