I would definitely make a complaint to the transit agency.
My mom rides public transit to work several days a week, as she has a very long commute (but has so much seniority at her old job that she did not feel like giving it up for a newer position closer to home - she retires next year, anyway). She was shocked that one day the bus driver on her route was texting - yes, TEXTING - while driving. She shrugged it off until the next couple of times she rode the bus with the same driver and he was still doing it. And driving like a maniac.
I've texted someone once or twice while on the road myself, but only at a stop light or if I was pulled over because I was lost) and only to let the person know I was on my way (to meet them) or running late or whatnot, because I couldn't get them on the cell for some reason. I am the queen of multi-tasking, but you can't tell me it's safe to text-message and drive at once. If you're texting, you are definitely not paying attention to the road.
Funny thing, ever since my mom called the transit agency on this guy, she hasn't seen him driving since. She doesn't know if he got a new route, but something tells me that's not quite it. My mom wasn't the only one who noticed him texting while he was driving...