Yesterday a tip of “undetermined credibility” about a potential terrorist plot to detonate a bomb-laden vehicle at an unspecified tunnel in the Baltimore, MD area led to the closure of the Baltimore Harbor Tunnel and stopped traffic through the Fort McHenry Tunnel, effectively shutting down I-95.

Law enforcement officers searched vehicles with bomb-sniffing dogs but found no corroborating evidence.

The information was originally under investigation by the F.B.I. and Dept. of Homeland Security (DHS) until it shared the tip with state and local officials. Maryland Gov. Robert L. Ehrlich Jr. said last night the tip has been under investigation by local, state and federal law enforcement agencies, The New York Times reported.

Maryland Transportation Authority Police initiated the Baltimore tunnel closure at around 11:27 a.m. and until 1:15 p.m. The Dept. of Homeland Security said, “we support whatever protective measures taken out of an abundance of caution,” in a statement.

The closure, which disrupted a major artery through Baltimore and caused backups throughout the day, raises the question of how terror-related tips are determined to be serious enough to warrant major highway closures.

“There’s been a debate on the credibility of the information for a while,” Don L. Rondeau, director of Highway Watch, an intelligence arm of a DHS program that taps transportation professionals. Rondeau declined to comment on how long DHS had been aware of the threat before contacting state and local officials.

“Eventually you reach a point where you’re unable to substantiate [the threat level] to the degree you’d like but still must consider others who are charged with the lives of citizens. You can’t fault the decision of shutting down a tunnel to potentially save lives. At the end of the day, you have to make a judgment call on the worst-case scenario—in this case it would have been catastrophic.”

Rondeau acknowledged that the pitfalls of shutting down I-95 extend beyond just traffic jams.

“The potential harm in that decision is the potential that we cry wolf-- that we react to these threats and shut down major arteries so often that when a real threat comes and we call on citizens to mobilize, they won’t,” he said. “I’m not questioning the decision, but I am saying that we have to develop a better way of ensuring we’re weighing all of our options so that when facing a threat we don’t shut down the country. It’s important that American citizens feel confident we’re communicating factual, actionable information and working to build a consensus [on threat assessment].”