On August 5, 2010, a pickup truck collided with a bobtail, leading to a pile up involving two school buses. Two people were killed, and 38 were injured. Texting by the pickup truck driver has been named as the probable cause of the initial collision, followed by inattention in the second bus collision, and following too close in the third.
The National Transportation Safety Board (NTSB) has released a report of their findings concerning the causes of the accident and recommendations about how to prevent future accidents.
You can read their report here. Note there is a link at the top for an archive of the December 13, 2011 webcast discussing the accident.