Wrt moving for wheelchairs, yep, would do this if required - have never been asked to, but I would. Don't need to now because my youngest is 5 and we just go and sit at the back of the bus anyway.
But regarding unsafe buses and accidents - DD lost two teeth being thrown out of her seat on a bus when she was 4. The driver mounted the curb at speed and DD was literally thrown across the aisle and landed on the edge of the opposite seat mouth first. Police and ambulance came, statements were taken - driver denied everything and bus company refused any responsibility.
I've also had an accident when the driver (same route) pulled away suddenly while I was helping youngest (then 3) into his seat. I was thrown backwards and hurt myself quite badly.
DS has also banged his face, and bruised it, on the seat in front when brakes have been suddenly applied.
I have 40 years of catching buses (at one point 8 day) and they're not safe places. I've seen pushchairs tip sideways and wheelchairs moving about too. I've also seen lots of pensioners thrown down the aisle because the driver has pulled away as soon as people are on the platform.
My biggest concern with them is how unsafe they are for passengers, all passengers.
If I knew the first thing about campaigning, I'd push for seat-belts and making sure the bloody drivers give people time to sit down before they start driving at breakneck speeds!
I know this is all irrelevant, just noticed the comments on safety.