In Pierce County, WA v. Guillen (537 U.S. 129 (2003)), Congress passed a law that said the results of State studies of traffic accidents were not discoverable in Federal or State Court. Congress felt that if the States thought that the traffic data could be used against them in courts, they wouldn’t make the studies at all (why would they gather evidence that could be used against them?). The Washington Supreme Court ruled that this was beyond Congress’ power. However, the US Supreme Court found that the law was constitutional because it falls within the power of the Interstate Commerce Clause to “regulate the use of the channels of interstate commerce’” and “‘to regulate and protect the instrumentalities of interstate commerce.”