Stephens says that because of the free flow of passengers on transit systems, security forces rely on passengers to report odd behavior or packages left behind:
"Widespread "See Something, Say Something" campaigns, including a text-based system started this summer by NJ Transit (see sidebar), are designed to take advantage of the countless pairs of eyes capable of spotting suspicious activity. Defining "suspicious," however, poses one of the biggest challenges to transit system law enforcement."
The Transportation Security Administration is also now involved on the local level of transit:
"Aside from their own intelligence gathering, the nation's otherwise diffuse network of transit agencies rely heavily on intelligence gathered by the TSA. The agency sends out daily briefs and frequently shares best practices."