My deepest sympathies to the people of London, especially to loved ones of those killed in today's horrific attacks, and those who were injured.
Tragically, attacking a major world city's public transit network at rush hour guarantees a high casualty rate, because terrorists can be assured that buses, trolleys and trains will be densely packed with people. (It's the same reason that trams in Sarajevo were such a popular target of Serb snipers besieging the Bosnian capital).
Now, residents of cities throughout the Western world will naturally be more nervous about taking public transportation - as many Israelis have been for years because so many of their buses have been the target of suicide bombers. Attempts to search and screen passengers getting on city buses - the response to airline hijackings and the 9/11 attacks - appear largely impossible without bringing the system to a crawl.
Londoners have been used to the threat of terrorism for decades because of militant Irish separatist activities, but today's attacks sadly bring the danger to a new and more lethal level. London must grapple with the issue of keeping citizen trust in the safety of its public transportation network at a time when the city has been trying to get people out of their private cars by charging them to drive autos in key center districts. It will not be an easy task.