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Traffic Ramp Metering Systems
Application: Network-Enabled Traffic Ramp Metering Systems
Quatech Products Used: QSE-400D
4-Port RS-232/422/485 Device Server and SSE-100D
one port RS-232 Device Server
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Ramp Metering is a common method of controlling highway traffic. As shown
in the diagram above, a typical ramp metering system will include a network
of loop detectors used to measure traffic flow. In addition, each ramp
is equipped with a set of queue detectors that measures the number of
cars waiting to enter the highway via the metered ramp. At the ramp, loop
detectors identify a waiting vehicle, and when downstream traffic clears,
the metering signal is turned green and the vehicle can progress through
the ramp onto the roadway. The check-out loop detectors tell the system
when the last waiting car has passed so that the signal can be returned
to red (alternately, the loop detectors can be used to allow a certain
number of cars to pass before the signal is returned to red and the wait
cycle begins.)
Traditionally ramp metering systems were controlled by roadside servers
that regulated the metering signal and tracked traffic patterns. However,
network-enabling the devices (as shown in the above diagram) in these
systems provides significant advantages both in terms of functionality
and implementation cost. Device servers can be placed near each loop detector
cluster along the roadway and connected to the underground fiber LAN already
in place along most major highways, thus eliminating the need for long
serial cable runs. In addition, rather than being stand-alone systems,
network-enabled ramp metering systems can provide valuable real-time traffic
data to the Traffic Management Center that can be used to alert motorists
to traffic jams, to pinpoint accident sites, to prevent traffic buildup
on secondary streets, and to analyze traffic patterns for future system
changes and improvements.
Further, because Quatech device servers enumerate themselves as standard
COM ports, this data can be accessed from any authorized PC or server,
just as if it were attached to the native serial port. This means legacy
systems can be network-enabled without any changes to proprietary software
applications while data from serial devices can be accessed and used by
any computer on the network--and even broadcast over the Internet. Quatech
device servers also offer the advantage of high-speed serial data rates
(up to 921.6 kbps), the industry's lowest latency, and the ability to
power serial devices at the port--all extremely useful features in data
intense ramp metering and traffic monitoring systems.
Other Intelligent Transportation Systems Applications:
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