Is that a Threat?

摘要

Bridges and tunnels are vulnerable to terrorist threats. Military tacticians have for centuries used available technology to destroy or preserve vital crossings. Commercial demolition experts routinely demonstrate the effectiveness of explosives to remove structures. And a captured al-Qaeda training manual shows ways to destroy bridges with improvised devices. Though this vulnerability is well understood, what is less well known is the answer to this question: What do we do to protect a vulnerable transportation system that is so important to the local, national and world economy?