Recently a new bus started from near my home. (http://www.e-bus.taipei.gov.tw/newmap/Tw/Map?rid=17740&sec=0)
It starts from A goes to B then goes to C then ends at D. In between B and C stops there is something called as 'buffer zone' as per the bus map.
I get on the bus before B and get down before C. How much will I have to pay? 15 or 30? It said on the bus map that 'Fare zone: 2X'
That's easy. If you take the bus passing B and C you need to pay 30. If not, it's just 15.
Example: You get on the bus at A and pay on boarding. After the bus passes B, the light sign indicates that you need to pay when getting off the bus. You only need to pay again when you get off after passing C, not before.
How does the driver know who paid when?! I seem to remember seeing some sort of card/token.
Some will just remember the people boarding, some will hand out the token to those getting on while the bus is in the buffer zone, some don't really seem to care.