“A tactic used by the federal government to gather information for anti-drunken and drugged driving programs is coming under criticism in cities around the country. The tactic involves a subcontractor for the NHTSA that uses off-duty but uniformed police at voluntary roadside checkpoints where motorists are asked on their behavior behind the wheel. Officers randomly wave motorists over; they are then asked by workers for subcontractor Pacific Institute for Research and Evaluation if they will participate in the voluntary survey. However, the mere presence of uniformed officers gives the checkpoints an aura of authority, says a senior staff attorney with the ACLU.”
http://www.usatoday.com/story/news/nation/2014/01/06/government-checkpoints-driving/4265633/