I believe this was the view from the bus approaching the crash site. Looks dangerous. Maybe it was a trick of perception where the driver just didn't see the center post, although he'd presumably driven the route many times. Or maybe he got blocked into it. It did look like he was in the left lane, which wouldn't have been the cautious choice.
I’m a bit surprised actually. That was acceptable engineering 100 yrs ago but most of those bridges have been torn our and replaced by now. At the very least they need some type of crush structure on the approach.