I'm not a bridge engineer, but I'm pretty sure that height requirements are there for a reason. In fact, I looked at this incident last week, and it seemed that there was a different maximum height depending on which lane you were in, but that was ignored/not acted on.
The vertical clearance from the roadway to the upper arched beam in the outer lane is 14 feet 7 inches (4.45 m), and all trucks with oversize loads are expected to travel in the inside lane where the clearance is around 17 feet (5.2 m). The oversize truck instead entered the bridge in the outer lane, while a second semi-truck and a BMW were passing it in the inner lane. ... A pilot car was hired to ensure the load could pass safely. The pilot car never signalled the truck driver that there would be a problem crossing the Skagit bridge and did not warn the trucker to use an inside lane.
