I don't want to be a pessimist, but in my opinion, there is no way we can stop the kind of attack I'm talking about once the players are in place and ready to pull the cord. The only way to prevent such an attack is during the planning stages before the enemy even sets foot in the transit station. I doubt even the best sharp shooter in the world could target the bomber among the thousands of commuters and then pick him or her off in the split second between when he yells "Allah Akbar" and when he pulls the cord.