I think it may turn out to be a combination of factors. Old Bridge. Traffic narrowed and slowed due to the construction. Maybe the jackhammer could have caused some harmonics. And I believe there was a train going under the bridge at the time.
I did not mean to imply that it was terrorism.
Just that when people say that it is unlikely because something requires knowledge, I get edgy.
That is a good way to underestimate your foes.