Starting Point - Initial Problem Statement.
Think where else the problem that you're solving can be faced?
Can this be a new problem statement?
Redefining how fare collection is done during journey.
Redefining how fare collection is done at other transport systems.
Think about the problem by multiplying your subject. If car was your problem subject, think of a car fleet (vehicles operated by car rental companies, taxicab companies, public utilities, public bus companies, and police departments), home vs. a colony, email vs. email server.
Keep broadening the scope of problem you're facing. From solving fare collection problem, look at solving the travelling problem itself, like redefining how fare is collected during journey.
Zooming-out on a problem: We look at how the problem statement can be made more common, at a broader level. Say if fare collection is your problem, then how about looking travelling as a problem?
Zoom-in - Think of the problem on micro-level.
Checking end-to-end Travel journey.
Checking that a person pays fare which is not for a station lesser than his travel.
By Zooming-in on a problem, we dig into the problem.
If this problem was to be solved, what sub-problems would you face?
Where to check for paying fare? At stop, on the bus, while boarding or de-boarding.
How to identify people who have boarded bus without paying fare?
Who to notify about people boarding bus illegally? What should the notification be?