[dennisw]

Railway damage may be a lucky break. The way I see it, the explosion from roadway damaged fuel train, setting it ablaze.
Instead of total explosion, burning fuel started to leak and flowed down the side of bridge, even reaching its underside. The fire was intense and went on for hours. Heat damage reached deep inside the bridge structure, making it too hazardous to use.

Reasonable theory. The burning fuel really did a number on the railway bridge. You know that railway bridges must be built and repaired much more precisely than a roadway bridge. Due to the heavy rattling loads. But how do you manage to hit the roadway and a moving fuel laden train at the same time? Lolzzzzz... The answer is that this train was stationary at the best possible location, for Lord knows what reason.

[TigerLikesRoosterNew]

It is possible that the explosion was meant to take out both the road bridge and a fuel train. But I am not sure counting on hours of heat damage from intense fuel fire was not part of the plan. It is too difficult to script it down to such a detail.