Post-9/11 I was in SoCal, and the mayor and LAX responded by not allowing any private automobiles to drive up to the terminals. They were very concerned about car bombs. At an airport. Why? I have no idea. There's no particular reason to set off a car bomb at an airport except for the fact that there are crowds, but there are crowds lots of places. They did let cabs and buses drive into the terminals. With a little thought you can probably get why this was very stupid.
At the '08 DNC the didn't let the light rail stop at the closest stop to the stadium, preferring to have people travel by bus. Of course the light rail is on a fixed guideway while a rogue bus driver can, you know, drive right into a building. This was all very stupid.
And, yes, most security at office buildings is also very stupid.
