nsponders can also use the tollway because digital cameras record rear license plate numbers as the vehicles enter and exit the road.
When a vehicle enters the tollway, its transponder networks via UHF with the RTC. Each RTC utilizes the Slotted Aloha Time Division Multiple Access (TDMA) protocol. (The protocol was originally developed by the University of Hawaii for military applications.) Hughes Aircraft has adapted the protocol for use with its Vehicle-Roadside Communications systems. A technique called
angle of arrival
, which enables the military to pinpoint enemy targets, can also, in a fraction of a second, identify specific transponders at any place and time, allowing for toll collection without slowing down at the RTC. Transponders, developed by Mark IV Industries, are mounted on the vehicle windshield directly behind the rearview mirror. Each has a communications frame of 10 milliseconds and creates a 915-M
Hz link using active communications and the Slotted Aloha TDMA protocol.
Slotted Aloha provides for concurrent communications at more than 500 Kbps with up to 272 vehicles at a time, regardless of the speed at which they're traveling. This accuracy allows the RTC to identify individual transponders within a fraction of a meter, so even motorcycles riding side by side, inches apart, can be separately identified.
"Equipped with Slotted Aloha, transponders provide 99.99 percent accuracy even in the high-speed, close spacing, and multilane conditions found on tollways such as the 407," says Martin Gray of Hughes Aircraft and project manager for the ETR 407. In addition to 125 RTCs, ETR 407 also includes two toll transaction processors that use asynchronous transfer mode (ATM) technology. These are located in a central administration center with a revenue management system.
Information collected by RTCs passes through fiber-optic cable to the transaction processors via an ATM network. Computer and imag
ing technology developed by Hughes matches the toll-road entry for each vehicle with the corresponding toll-road exit. This data is then relayed to the revenue management system, which handles all customer billing and collection functions.
ETR 407 is the result of a public/private partnership. Members include the Ontario Ministry of Transportation, Hughes Aircraft of Canada, Bell Canada, Bell Sygma Telecom Solutions, Mark IV Industries, and Canadian Highways International Corporation.
While ETR 407 is the world's first fully automated toll road, electronic toll collection is not unique to Ontario. In 1987, several toll agencies in the Northeast Corridor spanning New York, New Jersey, and Pennsylvania began investigating the potential of electronic toll collection. In 1991, seven toll facilities within the Northeast Corridor joined to form the E-Zpass Interagency Group (IAG). Accounting for almost 40 percent of all U.S. toll transactions and 67 percent of all U.S. toll revenues, the IAG wants to develo
p a cohesive, regionally compatible electronic system to streamline toll collection and to offer customers a transparent method.
Upon evaluation of several technologies, IAG is now implementing transponder technology from Mark IV Industries. Over the next five years, IAG members plan to install E-ZPass technology at approximately 200 sites, covering approximately 1500 miles of tollway, four tunnels, and 12 major bridges. The success of IAG's efforts represents the most significant move toward standardization of electronic toll collection in North America. Discussions between IAG and the Province of Ontario have taken place; however, at press time, Ontario hadn't committed to join the agency.
While it is the strength of the technology players that has driven regions such as the Northeast Corridor and Ontario to choose similar systems, much work has to be done to provide drivers with a continent-wide standard for toll collection. But the first steps have been taken toward a more efficient way of collect
ing revenue from busy travelers.
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