Or how effective is stopping all drivers approaching the airport and asking why they are at the airport. Do they really expect someone to say:
"Oh I am just going to drop off my van which is loaded with explosives."
The most effective anti-hijacking change that will ever happen, happened immediately when the planes hit the WTC. The men AND women on UAL #93 who refused to die in vain are great heros, but so are you and I and we will never ever let it happen again.