Pennsylvania's criminal law allows police to conduct sobriety checkpoints to enforce the state's laws against driving under the influence, or DUI. However, not all states in the U.S. permit sobriety checkpoints. Some of them have outlawed this particular police technique.
The reason why some states can permit sobriety checkpoints while others forbid it is actually a result of some of the most intricate and complex legal ideas about an individual's rights in the U.S.
Why Roadside Checkpoints Are Controversial: No Reasonable Suspicion
The Fourth Amendment is one of the most important aspects of the U.S. Constitution. It forbids police and other law enforcement officers from conducting “searches or seizures” that are “unreasonable.”
“Seizures,” though, span a spectrum of intrusiveness. Some, like arrests, are very intrusive. Others, like an officer asking someone a few questions or starting a conversation with someone on the street, are not very intrusive. When a cop can initiate a seizure depends on how intrusive the seizure would be.
While there is a lot of nuance, the general idea is that to comply with the Fourth Amendment, police need probable cause in order to make an arrest, but only reasonable suspicion that a crime is being committed to make a detention.
Roadside checkpoints are controversial because they allow police to pull everyone over, even if they don't have reasonable suspicion to believe that a particular driver has done something wrong. This sounds a lot like an “unreasonable” seizure that would violate the Fourth Amendment.
The U.S. Supreme Court Says Roadside Checkpoints Are Fine
However, the U.S. Supreme Court – the ultimate arbiter of what the Constitution says and means – has decided that sobriety checkpoints are not unreasonable seizures. In Michigan Department of State Police v. Sitz, the Supreme Court decided that sobriety checkpoints were not that intrusive if done in certain ways, and served an important public interest in reducing drunk driving and the accidents that it can cause.
Some State Supreme Courts Have Expanded Their State Constitution to Forbid Checkpoints
The civil liberties provided by the amendments to the U.S. Constitution, however, are only the bare minimum that Americans can enjoy. Each U.S. citizen is also a citizen of the state in which they live. Each state has its own state constitution, which is free to expand on the rights offered by the federal constitution.
This is an important legal concept called federalism.
Every state has its own version of the Fourth Amendment in their state constitution. In Pennsylvania, it is Article I, Section 8.
About a dozen states have decided to expand the rights afforded in their own state's version of the Fourth Amendment to require police to have individualized reasonable suspicion whenever they pull a driver to the side of the road in a traffic stop. In these states, police need to have a solid reason for pulling a particular driver over, meaning they cannot do it randomly, like in a sobriety checkpoint.
That is why some states prohibit roadside checkpoints, while others, like Pennsylvania, let police do them.