Security personnel approach the Detroit Windsor Tunnel, which was closed for nearly four hours July 12 after a bomb threat was phoned in on the Canadian side.
Three bomb threats closed two Detroit border crossings earlier this month, prompting national security concerns and threatening to slow auto supply chains.
Another threat prompted a search of Comerica Park, where the Detroit Tigers were playing a home game. No explosives were found in those cases, but the threats tied up traffic and forced federal agents, Detroit Police and their Canadian counterparts to scramble.
The threats in Detroit, following others the past year, including a series of threats at the University of Pittsburgh that disrupted campus life for weeks, are examples of an issue law enforcement authorities face all too frequently - the necessary deployment of resources and the disruption of daily routine for threats that often turn out to be just that.
Bomb threats are expensive because of the number of people typically called in to respond, said Steve Layne of Layne Consultants, a Denver-based firm that provides security advice to business, non-profits and governments.
"Hoax threats are not harmless pranks," said U.S. Attorney Barbara McQuade. "You don't have a bunch of people sitting on the sidelines waiting for those kinds of calls, so obviously you have to call in additional help."
Tracking the cost and the frequency of bomb threats is difficult because there are no official statistics for them, said Mike Campbell, spokesman for the Bureau of Alcohol, Tobacco, Firearms and Explosives. Some are handled by local police. Others, like those at some schools and universities, are tracked internally but not reported to other agencies, he said. Some are reported in the media, while others aren't.
Layne said most small police departments can't afford bomb squads so they typically partner with other small departments or count on larger departments or military units to help. Many bomb squads now use robots to inspect suspicious packages, but those are expensive, too.
"They aren't giving them away and you can't get them at Walgreens," he said.
It's also difficult to know how long a bomb scare will take to resolve as well. Layne said the situation in Auroro, Colo., where experts worked to dismantle explosive devices left in the apartment of James Holmes, the suspect in the theater shooting, ended more quickly than most experts expected.
Bomb threats also cost private businesses plenty. Two Wal-Mart stores in Newton County, Ga., were closed for about three hours last month after a threat phoned into a 911 dispatch center said a bomb was planted in a Wal-Mart without identifying which one. No bomb was found.
In Detroit, the recent bomb threats that closed Detroit's Ambassador Bridge linking the city to Windsor, Ont., got auto officials' attention. Ford spokesman Todd Nissen said the closure didn't disrupt production, but the company could lose as much as $1.5 million for an hour shutdown at an assembly plant.