Transmission Basics | Components | Applying Fiber Optic Technology | System Performance
Fiber Optic Intelligent Traffic Systems
Traffic JamTraffic control has been an issue since humans put the first wheels on the first cart. The modern world demands mobility. Cars represent the main method of mobility, but today's congested highways and city streets don't move fast, and sometimes they don't move at all. Intelligent traffic systems (ITS), sometimes called intelligent transportation systems, apply communications and information technology to provide solutions to this congestion as well as other traffic control issues. Intelligent transportation systems offer many types of information. They may offer real-time information about traffic conditions, such as variable message signs (Figure 1) to warn of Amber Alerts, accidents, or other delays. ITS controls the flow of traffic via traffic signals, or by opening and closing special gated lanes that allow commuters to access additional traffic lanes in one direction or the other, depending on the time of day, and the direction of the heaviest commuter traffic flow. Some applications provide fog sensors that activate road lights in areas where heavy fog can occur and cause extremely hazardous driving conditions. These fog sensors may also be used to send a message to a variable message sign located before the foggy section to warn motorists of the upcoming hazard.
Figure 2 — Traffic Sensor (left of center traffic signal) and Traffic Camera (right of center traffic signal).Regardless of the exact function of the ITS, fiber optic links offer a valuable component in the overall traffic network. Modern ITS networks require ever-increasing data rates and payload carrying capabilities to facilitate real-time communications between a wide variety of field devices and traffic control centers (TCCs). Single-mode optical fiber-based ITS infrastructures are displacing twisted pair copper and coax for both data and video transmission requirements in urban and rural jurisdictions worldwide. Video transmission for surveillance of intersections, ramps and tunnels, incident detection or verification, and replacement of traffic signal loop sensors is an increasingly popular ITS tool. Lately, communities have been installing cameras on traffic signals to record the license plates of cars whose drivers run a red light. All of these applications require distance between the site where the information is collected and the location where the information gets stored. Video transmission that incorporates 2-way data has grown as an ITS application. This system transmits video to a control center as well as data. The control center sends data to the remote camera that allows a PTZ device to be custom positioned as needed by the person at the control center. Fiber optic links for point-to-point FM baseband transmission over single-mode fiber from fixed or PTZ-equipped roadside cameras are widely available for distances up to 90 km. Intelligent transportation systems, as with many fiber optic applications, require a network of nodes, controls and signal paths. "Fiber Optic Network Topologies" discusses the various forms this and other types of networks can take.