In State v. Botero-Ospina, 71 F.3d 783 (10th Cir. (1995)), cert. denied, 518 U.S. 1007 (1996), the court considered the constitutionality of a pretextual stop. It said that a traffic stop is valid, inter alia, if it is based on an observed traffic violation.
The court upheld a stop made after the car swerved from the outside lane, straddled the center line, and swerved back to the outside lane; the police officer was concerned that the driver was either fatigued or under the influence of drugs or alcohol. Because lane straddling and driving under the influence are illegal under Utah law, the court concluded that the stop was "fully warranted." Id. at 788.