DWI Roadblock Guidelines from the Virginia Association of Chiefs of Police
Fairfax County Police run DWI/DUI roadblocks every week, weather permitting. Each week, they try to publish a press release showing which district will have a roadblock, usually Friday or Saturday night. Then, a few days later, they publish a summary of the results.
The 4th Amendment to the United States Constitution, along witn numerous Supreme Court cases, have set strict limitations on the ability of police to stop motorists without reasonable suspicion.
This document from the Chiefs of Police sets forth suggested guidelines:
Chiefs' Roadblock Guidelines