Illinois v. Lidster, 540 U.S. 419 (2004), was a case in which the Supreme Court of the United States ruled that the Fourth Amendment permits the police to use a roadblock to investigate a traffic incident.

In City of Indianapolis v. Edmond, 531 U.S. 32 (2000), the US Supreme Court ruled that police checkpoints set up for the purpose of "general crime control" were unreasonable under the Fourth Amendment.

Unlike the checkpoint in Edmond, the "primary law enforcement purpose" of the stop in this case was to "ask vehicle occupants, as members of the public, for their help in providing information about a crime in all likelihood committed by others."

The roadblock advanced the police's "grave public concern," but it "interfered only minimally with liberty of the sort the Fourth Amendment seeks to protect."

At the same time, the "likelihood that questioning a random sample of drivers will yield useful information about a hit-and-run incident that occurred a week earlier is speculative at best."

However, neither of the lower courts had balanced the relative factors weighing in favor of and against finding the seizure reasonable, as the per se rule of Edmond dictated the outcome of this case.