Ya know... I just laughed out loud listening to our head of Homeland Defense yesterday. He ran his mouth continually... talking about how secure our mass transit system was.
So... Dipshit Abu couldn't just put a bomb in a backpack... get on a bus... leave the backpack in his seat... get off the bus...
Do we search people gettin' on buses? How about subways? Do we search those people?
No. We don't. We can't.
There is no way to make the mass transit system a hard target. Its functionality depends on lots of people being able to get on, and off, very quickly. They have to be able to carry bags. They use the system to go to work... to shop... everything.
The government can talk till its blue in the face... but nothing will ever secure a mass transit system without reducing it to uselessness. Look at the damage done to the air travel system. It's nearly useless now, and its anything but secure.