While vacationing, the surprise on boothless and cashless toll roads is not the cost of the tolls themselves, but the often exorbitant rental-car surcharges for incurring them. (iStock)

Whether you’re heading down to Florida for spring break or out to Denver to go skiing, you need to know about one of the worst kinds of tourist traps you could fall into.

In Orlando, it’s called State Road 528, also known as the Martin Andersen Beachline Expressway. In Miami, it’s Florida State Road 112, also called the Airport Expressway. In Denver, it’s E­­-470, which connects the city with its international airport.

Not only are these toll roads opportunistically built next to airports, they’re almost entirely cashless, meaning there’s no booth where you can pay your toll. If you don’t pay, the systems generally take a photo of your plates and send you a bill. Too often, out-of-town visitors find themselves driving rental cars on these roads — and accruing surprise charges in the process.

The surprise is not the cost of the tolls themselves, but the often exorbitant rental-car surcharges for incurring them.

“The whole system is rigged in favor of the rental car companies,” says Cynthia Rigatti, a consultant from Mill Valley, Calif., who inadvertently used a cashless toll booth on a recent visit to New York and incurred a $4.95 per day transponder charge from Hertz, even though she never used another toll road or bridge on her trip.

There are ways to avoid these charges, and no better time to know about them than now, when they are generating more profits for rental car companies than ever before.

Knowing that boothless toll roads exist and planning ahead is perhaps the most effective way to steer clear of them. You can also bring your own toll transponder and have a plan for handling any dispute that may arise if you receive a bill from your car rental agency or tolling authority. Or you can do both.

Phillip Singleton, a political consultant who is used to navigating Florida’s toll roads, favors the plan-ahead approach. His preferred app is Waze, which offers crowdsourced driving directions that show you how insiders get from point “A” to point “B.”

“Not only do they have faster routes,” he says, “But in your map setting you can choose to avoid tolls.”

Zaida Khaze, a small-business owner from Fort Lee, N.J., frequently rents cars in the New York area, and has learned to never trust the GPS systems in the cars. Why? “They always chose routes with tolls,” she says. Instead, she turns to her smartphone. Google Maps allows her to plot a course with no toll roads. “That saves me,” she says.

Robert Herbst, an attorney in Larchmont, N.Y., brings his own transponder — E-ZPass — when he rents a car. E-ZPass, which works in 15 states, allows you to transfer a transponder between vehicles as long as they are of the same vehicle class. He registers his rental car with a quick call.

That doesn’t guarantee the car rental company’s transponder or plate registration system won’t also kick in, double billing you. To avoid that, Herbst always tells rental company employees in advance that he plans to use his own transponder.

“I have found that most car rental companies back down on issues if you act like you know what you are doing and don’t take no for an answer, in a firm but polite way,” he says.

And when they don’t? Herbst has received a bill or two from rental companies when he used his own transponder, and has successfully disputed the fees. Of course, it helps that he’s both a lawyer and a world champion powerlifter, each of which can be quite compelling in their own way.

If you don’t have a transponder, or yours doesn’t work at your destination, you can always buy one. In Florida, for example, a SunPass Portable transponder costs $19.99, or you can get by with a SunPass Mini Sticker transponder for $4.99. You can buy them at Publix, CVS and Walgreens. Both units allow motorists to have tolls electronically deducted from prepaid accounts. SunPass also has a helpful page for car-rental customers.

Even when you’re stuck using your car rental company’s transponder, there’s still hope, says Mark Mannell, chief executive of CarRentalSavers.com, an auto-rental site. All-electronic tollways in Texas and Maryland allow drivers to pay online quickly, he points out: “This allows you to avoid any administrative fees that the rental agency charges.”

(Tolling authorities recommend that you contact your rental company before doing so.)

Perhaps the most important thing to remember is that you’re responsible to the tolling authority, not the car-rental company, for settling your debt. If you can demonstrate that you have paid your toll but a charge appears on your bill, you can dispute it via your credit-card company.

The industry probably will roll over long before it gets to that point. The reason? Companies don’t want a credit-card dispute, and they definitely don’t want the dispute litigated. Should that happen, it could eventually set a precedent that the industry doesn’t want — but which consumers urgently need.

Elliott is a consumer advocate, journalist and co-founder of the advocacy group Travelers United. Email him at chris@elliott.org.