That was a great suggestion. The problem is we don't have Kreskin the Mind Reader in the US government to predict what terrorists are going to do. In my experience you rarely had advance notification that some group of individuals are going to carry out an attack against some target. The threat warnings, when you get them, are so vague and difficult to act upon that it lulls people into complacency. But what we do know is that if you will simply follow the recommendations that Admiral Inman made about hardening facilities, building walls up, set back from the street, that there's a physical limit to how many explosives someone can pack into a van or a truck.
Hijackings go down.
When you put in place measures that make it more difficult to put bombs onboard planes, bombs don't blow up on airplanes. When you put in place security measures which make it more difficult for people to put a vehicle next to a building and leave it unattended, car bombs don't happen.