Understanding tolling systems before you hit the highway.
Some countries use traditional cash or card booths, others use fully electronic tolling with no way to pay on the spot, and a growing number use license-plate cameras that bill your rental company directly. It's worth asking your rental agency which system applies to your route.
Electronic-only toll roads sometimes carry an administrative fee on top of the toll itself when billed after the fact, so a prepaid toll pass, where available, can work out cheaper for a longer trip.