Add the weight of the truck itself. That would be a difficult object to stop. What do they do, shoot at it? And make it blowup enroute in a very crowded city?
Based only on publically available information, you've come up with a very plausible scenario. Certainly racing toward a crowded convention center and detonating a hole in the tank during the last seconds as it closes on the center could/would create quite a terror event.