Here is the link to the AP video report containing info from a police official who said the driver survived and also went back into the bus several times. The clip is short, and doesn't contain a lot of info as far as cause due to it being an early report.
http://www.latimes.com/news/nationworld/nation/la-092305rita_vid,0,396967.wmvfile?coll=la-home-headlines
That God for people like the driver of that bus. He risked his life to save as many people as he could.