Let's start out with something simple. The Fourth Amendment to the Constitution: The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized. If a police officer on the street, for no cause, stops you, he has effectively seized your person. As free citizens, such seizure is in violation of the Fourth Amendment unless other circumstances exist. For instance, if you are acting in a suspicious manner then the police officer might have cause to stop you and investigate the situation. In such situations he can further perform a "Terry Stop" or "frisk" you for his own safety. Such an action is restricted and has been deemed Constitutional through various court cases. However, the original cause of the stop (the seizure) of your person still has to exist.
So, we have a traffic stop situation. There are several common causes for traffic stops:
- The police officer has witnessed you committing a moving violation of the traffic law
- The police officer has observed an equipment malfunction on your vehicle
- The police officer believes that your vehicle or you (as the driver or passenger) match a description of a wanted person or vehicle connected with the investigation of a crime
- Arbitrary and impartial enforcement activity is on-going, such as Drunk Driver Check Points
Let's consider this situation very carefully:
If you HAVE NOT committed a moving violation, and
If you HAVE NOT got any equipment malfunctions on your vehicle, and
If you HAVE NOT got anyone in your car that matches the description of a wanted person or the vehicle doesn't match, and
If there is NO specialized enforcement activity going on, then
How does the police officer - or his agency - justify "seizing" you? That is effectively what he's done when he stops you and robs you of your freedom of movement (in my opinion).
Now certainly there can be circumstances that exist wherein the police officer would be justified in stopping you. Let's use a crime scene area as the example. If a crime is committed and there is a crime scene that is under investigation then access to or through that crime scene obviously has to be controlled. Often this means stopping people in their travels and not permitting them into a given area. Such an action is completely justifiable during the on-scene investigation of a crime.
How about if a given area has an existing threat in it? When I was in the Army as a Military Policeman, we closed all access to a base hospital because of a bomb-threat that had been called in. There were quite a few service members who were upset that we wouldn't let them IN to the hospital. But we had a good reason for keeping them out: a potential threat existed inside and it would have been irresponsible to let them go walking into an area where they could be killed.
And with that very thought I felt I had come up with what Washington DC's police department might be using for the justification of its actions: By stopping the free movement of American citizens into a given PUBLIC area, it might be saving their lives. Why? Because the violent crime rate within that given area was (is) SO high that there is a real risk to those who enter it. What is the biggest difference between THAT set of circumstances and the one of a hospital on a military installation?