When I look out my front window, I see a major street, then train tracks, then the Mass Pike.
The train rings its bell when it goes by. So, I know, even while I'm still in my house, when I've missed the train.
Why doesn't the bus have a bell? It only comes once every 25 or 30 minutes at certain important times of the day. And it does not stick as closely to its schedule as the train does. In fact, there is no schedule that says exactly what time it is supposed to be at my stop, because it's not a major stop.
So I'm frequently faced with the angst-ridden decision of whether to wait for a bus that may already have gone by.
If anything needs a bell, it's the bus.