Even if the bison was 6' tall & 2K pounds, you would think it couldn't knock an 18 wheeler pulling about 20K#s of salt off course. Maybe he saw it right before impact and understandably jerked the wheel or something. It would be scary to see something that big appear at 3AM right in front of you. The media said that guy was a driver for 50 years & never had a chargeable accident.
Sad for sure.