I know that bridge very well. I can tell by the shadows that this is the westbound side of the freeway. As you hit the bridge, you hit a big bump that should have been repaired long ago before something like this happened. I'm betting that he hit the bump and the trailer started to sway. I've been tossed by it a couple times just in the last year, luckily never pulling a large trailer.

“In a time of deceit telling the truth is a revolutionary act.”
― George Orwell

It's not over when you lose. It's over when you quit.