Can a police officer search me if I am a passenger in a car that has been stopped for speeding?
Generally, no. The rules surrounding the search of passengers in a car stopped for a moving violation are similar to the rules surrounding the driver. That is, if the officer has an articulable suspicion that the passenger may be involved in criminal activity, the passenger may be searched. For example, if when approaching the car, the officer notices the passenger bend over and hide something under the seat and the car smells like marijuana when the officer approaches, the passenger may be searched.
Whether or not the passenger (or driver) have actually done anything to create an articulable suspicion that a crime has been committed is usually a hotly contested issue.