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How E-ZPass Works

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E-ZPass MA Program

transponder attached to windshield

The E-ZPass system uses a small electronic device, called a transponder, which attaches to the inside of your front windshield (as shown in the picture to the right).

As an E-ZPass equipped vehicle travels through an electronic toll collection (ETC) lane at a toll plaza, the transponder identifies the vehicle as a participant in the program and gives the vehicle a green "Thank You" light indicating the transponder has automatically recorded your toll transaction to your E-ZPass account.

If you have a valid transponder and your account is in good standing, you should see the bottom green "Thank You" light indicating that your transponder has been read and processed. If you see the middle yellow "Low Bal" light  (Low Balance), your account needs to be replenished. If you receive the top yellow "Call E-ZPass" light it indicates the following: You were recorded as a violation and you are required to contact Customer Service, to determine why your toll transaction was not recorded. You are required to stop using your transponder until you have contacted Customer Service where your transponder was issued from and verified that your account is in good standing and that your transponder is working properly. If you disregard the message and continue to use your transponder, you will be issued violations. A violation in Massachusetts results in a $50.00 fine per occurrence.

Technology Background

Electronic Toll Collection (ETC) systems are a key component of intelligent transportation systems (ITS) that are being utilized by transportation authorities around the world to make traveling safer and more efficient. This ITS initiative utilizes a variety of technologies to improve the movement of people and goods via highways and public transportation. For example, high-speed electronic tolling systems, such as E-ZPass, mitigate congestion, decrease waiting times, and reduce pollution.

Technology and System Design
The E-ZPass MA system consists of three inter-related subsystems that are linked via a fiber optic communications network to the Customer Service Center. The three subsystems are:
  • Automatic vehicle identification
  • Automatic vehicle classification
  • Violation enforcement
Automatic vehicle identification
As your vehicle, with a transponder properly attached on the windshield, approaches an E-ZPass MA lane at a toll plaza, the transponder begins communicating with an antenna in the lane. The ID number that is programmed into the transponder is verified by a computer in the lane, the account to which the transponder is assigned is looked up to determine whether it is in good standing, and, if all is in order, the toll transaction is posted in the lane and recorded in the memory of the tag, and you will see a green "Thank YOU" light. All of this occurs in milliseconds while your car is in a read zone approximately 10 feet in length. The transponder is a 2 way radio and microprocessor, operating in the 900 mHz band.
Automatic vehicle classification
The amount of the toll you pay is based on the number of axles and wheels on your vehicle, as well as where you are traveling. Classification of vehicles in an ETC lane is accomplished through the use of automatic sensors that count axles, detect dual wheels, and count vehicles with a high degree of precision.
Violation enforcement
In each ETC lane there is a front and rear digital camera that captures images of the license plate of every vehicle that passes through the lane. If this vehicle is determined to be a violator, images are transferred to a violation center for processing.
System Specifications
Throughput: 2,000 vehicles/hr/lane
Transponder Density: One transponder per vehicle.
Accuracy: 99.9 percent
Security: Tag-to-tag reader communications use error checking.
Operating Frequency Band: 912.750 to 918.750 MegaHertz.
Transponder Operating Temperature: -40 degrees F to 158 degrees F
Interior Transponder Attachment Method: Fastener strips
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