SECURITY
Beyond all the other problems with this scheme, none of which are small, people are missing one important fact about terror bombings. The point of a bombing on a subway is not to blow up the subway, it’s to kill people. If I have a bag with a bomb in it and a cop stops me right at the entrance to the subway, why wouldn’t I just blow the bomb right there? There will be lots of people around because a cop randomly searching people will cause a backup and a crowd just by being there. Plus I get the benefit of closing down the entrance to the subway for an unknown period while they repair any damage. And if I get through, which is the far more likely senario, I still get to blow up the bomb wherever I want.
Once again this is a pointless measure that puts us one more step down the road toward a police state.