Rental car companies increasingly offer transponders for cashless tolls, but in some cases, travelers end up paying more than they need to. As cashless tolls become more prevalent, drivers without transponders can find themselves on roads where they have no immediate option to pay. Instead they often receive a mailing based on an image of their plate taken at the toll. In the case of rental cars, the notification goes to the company.

If you don’t sign up for an electronic toll pass, some companies tack on an administrative fee — as much as $15 — for each cashless toll encountered. And if you do, some companies charge a daily fee of $12 or more for the pass, even on the days when you never hit a toll.