[HairOfTheDog]

But, if those leads are so vague that they cannot narrow their searches to a reasonably small number of vehicles, I think they have to take a less agressive stance towards vehicle occupants, in order to accomplish their ultimate goal, which is to ensure the safety of the general public

Vague or not... They are operating in the hope and dread that the guy they are after is trapped in that backup. You tell the cop to walk up to those cars without someone ready to act if they've got him.

[B Knotts]

Well, using that logic, why not simply do door-to-door no-knock raids in a 100-mile radius of Washington, D.C.?

The police would be armed and ready to shoot, and since they're professionals, the residents have nothing to fear.

Putting aside the constitutional problems with such an idea, don't you think another major argument against doing this would be that it would needlessly put the lives and safety of very large numbers of innocent citizens at risk? That is my point. There are entirely too many innocent people in the class of "people driving white vans" to be pointing loaded firearms at all of them.