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Electronic Toll Collection
Application: Network-Enabled Electronic Toll Collection
and Surveillance
Quatech Products Used: DSE-400D
2-Port RS-232/422/485 Serial Device Server
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Electronic Toll Collection systems, such as the popular EZPass system
employed across several North Eastern US states, are becoming an increasingly
popular way to both speed toll collection and to monitor driving patterns,
traffic movement, and congestion problems. As shown in the diagram above,
the typical system consists of a transponder or "smart tag"
located in the vehicle that is accessed by a tag reader (located on an
overhead archway) that is connected to one port of Quatech's DSE-400D
device server. The vehicle is tracked at the toll entry point, and a flat
toll is immediately assessed, or if a variable usage toll is employed,
a second smart tag reader at the exit will access the smart tag and assess
the appropriate fee. This dual point system can also be used to track
traffic patterns, measure the average travel time between two toll points
to indicate traffic slowdowns or potential accident sites. To prevent
"toll-skipping" cameras are typically co-located with smart
tag readers in order to photograph drivers attempting to pass without
paying. These images can be relayed to upstream patrol cars, or can be
recorded for subsequent prosecution. While a fixed camera is acceptable
for many systems, the ability to control the positioning of the camera
is a useful addition. Using the second port on the DSE-400D as an RS-422
interface, Pan-Tilt-Zoom control of these cameras is easily accomplished
via remote control.
Network-enabling the serial electronic toll collection equipment significantly
increases its value as a traffic management and control instrument. In
addition, it enables the system to comply with NTCIP requirements that
the devices be available to all authorized jurisdictions, in addition
to the Traffic Management Agency that owns the system. With device servers,
the remote serial equipment can be network-enabled using the fiber LAN
network already in place along most major roadways. The devices can then
be accessed by any authorized PC or server on the network, regardless
of operating system, just as if it were directly attached to a local COM
port. And, while only one computer at a time can access a particular port,
multiple computers running different operating systems can access different
ports on the device server simultaneously--thus the toll collection agency
can be constantly polling the tag reader using a Windows system at the
same time a police agency running a Linux system accesses the camera PTZ
controls.
Quatech device servers are particularly well suited for this electronic
toll collection system because they offer the industry's lowest latency.
Particularly in heavy traffic locations, electronic toll collection is
a polling-intensive application. This heavy polling is increased further
when multiple jurisdictions (at predetermined intervals) access the smart
tag reader or reposition the camera. Quatech's high performance device
servers in ultra low latency mode offer the speed and reliability required
to keep electronic toll collection systems functioning flawlessly.
Other Intelligent Transportation Systems Applications:
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