What is the test for reasonable suspicion in a traffic stop?

The district court's conclusion that reasonable suspicion exists and justifies an investigatory stop is reviewed de novo. See United States v. Hernandez-Alvarado, 891 F.2d 1414, 1416 (9th Cir.1989).

Reasonable suspicion exists if "an officer is aware of specific articulable facts, that, together with rational inferences drawn from them, reasonably warrant a suspicion that the person to be detained has committed or is about to commit a crime." United States v. Salinas, 940 F.2d 392, 394 (9th Cir.1991). Even if the facts viewed alone do not reflect any illegal activity, viewed as a whole they may support a finding of reasonable suspicion. See United States v. Malone, 886 F.2d 1162, 1165 (9th Cir.1989).