Hi! It is the same situation as in implementing the keyboard. Sometime, if you don't want to spend a lot of time to scan the keyboard, you can use OR gate for each row (or column). After pressing the key, your OR gate is generating interrupt request and after this you can recognize the key. Maybe it is solution for you. If your indicator detects car, you can go to the interrupt routine and recognize the source of interrupt and increment one of your car counters.
In case like that, I prefer ST6225 (or 20) controller. Each of its ports' pins can be used as interrupt request input. ST62 is very slow (it has serial accumulator) but maybe you can use it.

Regards,
Jacek