The Amazing E-Z Pass

Today we’re going to talk about the E-Z pass. You’ve probably seen one of these card-deck-sized devices mounted on the inside of a windshield. The radio inside it allows a person’s account to be charged automatically for using a toll road.

We’ve had toll roads in America since 1792, when the Philadelphia and Lancaster Turnpike in Pennsylvania was chartered. Charging tolls made it possible to build and maintain the first real roads in our young country. The popularity of toll roads waned during the mid-20th century, displaced by a vision of a national highway system built with US tax dollars, not tolls. As these roads aged and degraded, however, communities again began to reconsider tolling to create, upgrade, and maintain local highways. Also, technological developments now made it possible to reduce the costs of collecting tolls. The first E-Z pass went into service in 1993, and the technology has been spreading ever since.

To understand E-Z pass’ benefits, you have to know how cumbersome paying tolls could be before this technology came along. As you entered the highway, you slowed down and stopped at a toll booth. A person physically handed you a ticket (in later years, a machine spit out a ticket for you) that listed all the highway’s exits and the associated tolls. The ticket was marked or punched out to denote your entry point. You drove along the highway until you got to your exit. You exited and approached another toll booth, where you gave another person your ticket and cash. Toll roads didn’t accept credit cards. There weren’t easily-accessible cash machines on every corner in those days, so you always had to leave home with the cash you would need on the toll road. Each toll-paying transaction took time. If there were high traffic volumes, you could get stuck for hours waiting to pay your toll. My record occurred during the Thanksgiving holidays one year when I waited five hours to pay my exit toll on the NJ Turnpike!

And then the E-Z pass came along. An E-Z pass is an example of RFID technology. RFID stands for Radio Frequency IDentification. Just like radar, an RFID can be active or passive. An active RFID tag has batteries and a passive one does not. An active tag emanates its own identification signal over a longer distance but costs more to produce. It also costs more to maintain because its batteries wear out and need to be replaced. A passive tag has no battery to be replaced, but it has a shorter range. It doesn’t have a power source, but placing it in an electromagnetic field induces a current so that the RFID can chirp out a message.

The E-Z pass is an active RFID. It contains a microchip that stores and processes information, a battery, an antenna, and the ability to transmit and receive signals. This combination of elements allows the E-Z pass to work seamlessly with the automatic tolling system. In simplest terms, it’s like a two-way radio.

So how does the E-Z pass system do its job? Tolling occurs when an E-Z pass-tagged vehicle passes in proximity to an antenna connected to the tolling system. In some jurisdictions, you have to slow your vehicle down a lot (like to 5 mph!) to pass through a conventional toll booth where the antenna is mounted. Newer toll roads eliminate the booth altogether, replacing it with an antenna on a bar over the highway under which fast-moving vehicles can pass quickly.

The tolling system sends out a signal over its antenna in the 900 MHz range. Receipt of this signal prompts the E-Z pass to respond with its identification number and account information. The tolling system antenna captures this data and sends it over its network to the centralized toll accounting system, which posts the charge without delay. If the vehicle doesn’t have an E-Z pass, no problem, the system has taken a photograph of its license plate number and will send its driver a bill.

How does E-Z pass save money? Toll roads no longer have to spend money on toll booths or people to staff them, resulting in huge savings. Sure, now they have to buy the technology to create the tolling system, but that costs a fraction of the old system. Another benefit is that high traffic volumes can now flow through the tolling system without delay, saving both time and gasoline.

Wow, that’s amazing! How did anyone ever think of that? Funny you should ask. The first person to hold a patent for what would become the E-Z pass was a man named Mario Cardullo. As a kid, Cardullo learned about a World War II technology called Identification, Friend or Foe (IFF). IFF was a radio technology that allowed a fighter to broadcast a message identifying itself to other aircraft as friendly (or not-friendly). As an adult, Cardillo had a chance encounter with an engineer in 1969 who was having problems building an automatic identification system for railroad cars. Remembering IFF, Cardillo sketched out an elegant solution for the engineer. This exercise was the origin of what would become the E-Z pass. You can read Cardillo’s account of this story for yourself at:

So now we’ve learned a bit about the origins of and technology inside the E-Z pass. But I’ve told you very little about the technology that inspired it, IFF. In next week’s blog, we’ll talk about IFF from the time of its invention up until the present.