For the majority of the time (outside rush hour at least), there's enough room on most buses for people to get on (the ablebodied to get a seat upstairs) and room for several buggies/suitcases/wheelchairs.

The problem and the bitterness only arises when the buses are already crowded which tends to be at peak times when we're all either trying to get to work/school/nursery on time or on the way home when we're tired/stressed from the day. That's when most of us probably feel that we deserve to be on that bus and tough for everyone else.

In those instances, it probably is 'first come, first served' in the space. If there are 20 passengers already standing in the area (with no seats upstairs/down) then it's unlikely the driver is going to stop for a buggy in any case. Wheelchairs, I guess they should but I wonder how many do - assuming that it's less hassle to try to get the 20 sardines off the bus again.