The bombing of three subway stations and a bus in London on July 7 brought into stark relief, once again, the ongoing threat to New York City. New Yorkers have long known that their city -- and its often jam-packed transit system -- is a prime target of terrorists. While the city's residents and visitors may sometimes set aside the risks, one would be hard-pressed to find anyone who is not aware of the possibility of another terrorist attack.

The London bombings also cast the spotlight on the NYC transit system's snail-like progress in spending nearly $600 million to improve security in the subway system. Two and one-half years after announcing the completion of a thorough security review, the Metropolitan Transportation Authority (MTA) reportedly has spent only $30 million of that sum, mostly on studies and consultants. Boston and Washington have deployed sensors to detect the presence of biochemical agents in the subway system. Houston has closed-circuit television cameras that can be used for surveillance. Atlanta upgraded two-way radios to allow transit workers to communicate with police and rescue workers. Compared with these efforts, New York lags behind.

Reaction to this news was predictable. Senator Charles Schumer called for a "crash program" because terrorists "have chosen mass transit as their target of choice." Mayor Michael Bloomberg called on the MTA to "ratchet up the pace of increasing security on our subway system." Mayoral candidate Anthony Weiner said, "It's not money that's standing in the way, it's bureaucratic foot-dragging that's stopping the MTA from doing it."

According to press reports, the MTA plans include
• strengthening transit facilities against explosives
• restricting access to sensitive areas
• detecting intrusions
• surveillance
• and communications systems.

These are clearly valuable security improvements that will improve the MTA's ability to monitor and respond to possible security threats.

While spotlighting the transit system's vulnerability, reaction to the London bombings also highlighted New Yorkers' sophistication in understanding and responding to the terrorist threat. A simplistic reaction to physical threats would be to seek absolute safety, no matter the cost or consequences. The power of this reaction is seen in the newly fortified design for the Freedom Tower at the World Trade Center site, and NASA's struggles to define acceptable level risk and safety after the two shuttle accidents. Discussions between the MTA and the Army, reported by the Times, aiming to develop motion detectors, infrared sensors and sophisticated software to monitor subway tunnels and other infrastructure also evidence the notion that the system can be "hardened" to repel attack. The comment in a television interview by Michael Chertoff, the Homeland Security chief, that "there is a technological and a system-based solution for this" is another example of this way of thinking.

New Yorkers do not seem to be buying the idea of absolute protection, however. On-street interviews carried in various press reports show a public partially willing to accept, partly trying to deny and partly attempting to rationalize the risk of terrorist attack. Mainly, the public seems to be trying to get on with life, knowing that they can neither avoid nor prevent what officials in London called a "shock" but not a "surprise." As an example, it was notable that in the two days following the London bombings I sat through a series of day-long meetings with city staff and others without anyone even mentioning what happened in London.

Terrorism and transportation experts cite four basic tasks in dealing with the threat. The four are:
• Deterrence, such as police patrols and chemical-sniffing dogs;
• Prevention, such as intelligence to catch terrorists before they strike, "saying something" when you "see something" in the subway and erecting bollards around key buildings to keep truck bombers some distance away;
• Mitigation, such as hardening stations and tunnels to minimize the damage from an explosion; and
• Prompt response to minimize casualties, such as good communications between emergency response personnel and regular drills to sharpen response procedures.

None of these approaches are foolproof, but each has been shown to be effective in reducing the risk.

Experts such as Brian Jenkins of the RAND Corporation (In PDF Format) also emphasize creating a net benefit rather than simply displacing the threat or the threatened. Jenkins says that security measures "should not merely displace the risk toward other equally vulnerable targets" - for example, from train stations to equally crowded shopping malls. Todd Litman of the Victoria Transport Policy Institute (In PDF Format) points out that it would be counterproductive if people stop using mass transit and drive instead, since the risk of a fatal traffic accident far outweighs the risk of dying in a terrorist attack.

In addition to these practical considerations, there are larger dangers to overreacting to the London bombings. As Jenkins has said, "We cannot allow fear to become the framework of American governance." Thus, we will continue, as Susan Jacoby wrote in Newsday, to try and do "a very good job of not thinking about what I know perfectly well - that it is absolutely impossible, in a city the size of New York, to make the subways and buses and public buildings safe from bombings."

Meanwhile, New Yorkers might feel a bit safer, and a bit more in control, if we act on the advice from the ad in the subway, "When you see something, say something."

Bruce Schaller, who has been in charge of the transportation topic page since its inception in 1999, is head of Schaller Consulting, which provides research and analysis about transportation. He is also a Visiting Scholar at the Rudin Center for Transportation Policy and Management at New York University.