Yep, they claimed it was an accident, but it would be a helluva coincidence that they happened to dump just as the bus was passing over a grated bridge over a river, wouldn’t it? You’re only going to be on that bridge for maybe 30-45 seconds unless you’re stuck in traffic, that’s a preposterously tiny window to stumble into if you aren’t intentionally dumping.
Here is the story. Apparently, it wasn’t an accident.
http://www.chicagotribune.com/chi-0503100266mar10-story.html