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:

• Network-enabled electronic toll collection system
  
  
• Network-enabled traffic information system (device server)
  
  
• Traffic information system (USB)
  
  
• Network-enabled red light camera system
  
  
• Network-enabled remote traffic monitoring system