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Dallas/Fort Worth (D/FW) International Airport's Transit Monitoring System
You need a watch with a second hand to time air traffic at D/FW International Airport. During peak periods, airplanes arrive or depart approximately every 36 seconds on one of seven runways. The airport is capitalizing on its central location, moderate climate and highway and rail connections, all of which make it an efficient way to travel and ship cargo to destinations in North America and around the world. As a result, the airport is expected to be the world's busiest by the year 2000. While these statistics fuel efficient business operations and low unemployment rates, they represent a major challenge for the airport's support mechanisms. Each year, the airport's transit system, for example, moves nearly 60 million travelers as well as the airport's 37,000 airline and support employees. Heavy air traffic and large distances make the airport a challenging place to shuttle people under any conditions, and the airport's automated guideway transit (AGT) system is one of the oldest and the most complex in the country. The transit system is also one of the country's most efficient-consistently achieving 98 to 99 percent reliability.
"Every airport transit system in the country wants to achieve our numbers because we are at the top," says Airport Train Manager, Ron White. "And everyone wants to know how we do it with a system that was designed and built in the early 1970s." The answer, he says, is due in large part to a computer-driven monitoring system that combines an efficient in-house application program with the long-term equipment reliability and support by its selected computing platform vendor. The transit system was designed, built and tested from 1972 to 1974. White participated in that process. "We started with blank paper on the drawing board because there was no operating airport transit system to study," White recalls. "Instead, we worked with other companies who were building prototype public transportation systems to learn all that we could about operations," he notes. Working with the design team, in-house programmers created a powerful application in Assembly language that continues to the present day. "We called in several outside consultants to evaluate rewriting our application software for the UNIX environment, but they all advised against it," White reports. "What we have works so well that we can't justify an upgrade. That's a tremendous compliment to the application's original developers and those who have continued to embellish it along the way." The team has been equally fortunate with the monitoring system's real-time computing platform, supplied by MODCOMP of Fort Lauderdale, Fla. More than two decades after installation, White has just completed his second upgrade to computers at the transit system's central command station. Additional computers located throughout the transit system and at the maintenance facility were last upgraded in 1985. "One of the advantages of this platform is that it is reliable. Equally importantly, new generations are designed to support previous systems," he explains. "Long-term users like ourselves are able to make systems last for decades with a few cost-effective upgrades." The guideway transit system features 14 miles of track, with six different routes. Some routes link terminals and are designed for connecting passengers. Others link terminals to north and south remote parking lots. Two controllers are on duty at the command console for most of the train system's 24-hour service schedule. One controller monitors the 480-volt guideway power and handles train malfunctions. The other controller supervises train operations and calls for more trains when stations become crowded. Malfunctions range from air conditioning outages to problems with braking or propulsion systems. If a brake exceeds temperature, for example, the controller will monitor the system and try to get the train into the next station where it can be offloaded for maintenance. In cases of scheduled or unscheduled maintenance, power can be shut down temporarily on a section of track, and reactivated when procedures are completed. Buses provide transportation for designated routes until train operation is restored. One computer at the central command station monitors system operations by communicating with nine remote computers. An additional computer performs off-line programming, testing and backup. The computers in wayside stations handle input and output commands to trains operating in the area. They poll trains for status updates every 200 ms. If two or three cars are linked together, the lead train car collects input from the others and reports it to the designated host computer. White and the maintenance staff recently upgraded the command center computers to reach a system configuration designed to last for the next 10 years. "The entire airport is being evaluated to develop a master plan to support aggressive growth. As part of that plan, we anticipate retrofitting our existing transit system, or building a completely new system. Our current transit system needs to last until the new or updated system can be designed and completed." The newly installed computers provide enhanced reliability with multi-layer boards. They supply forward compatibility by supporting both 16- and 32-bit processing and are backward compatible with previous generation equipment, which exists in wayside stations throughout the transit system. Although White does not plan to upgrade to 32-bit technology, he can do so at any time by recompiling the application program, avoiding a costly software rewrite. In that case, the central computer, operating with a 32-bit operating system and application software, would continue to interact with existing 16-bit computers located throughout the system.
While efficient transportation is the goal of the transit system, safety is the first priority. For that reason, the computer-driven monitoring system can modify train speed, direction, and other factors but it cannot override the built-in safety system. "Our system is designed to ensure safe delivery of passengers to their destinations. There is no way that a computer or a controller can put a train into an unsafe situation. The system simply won't allow it," White explains. To properly manage resources and cut costs, the number of trains placed into service is adjusted to match passenger traffic predictions provided weekly by the airlines. "During peak periods of the day, we have more trains on the track. Likewise, some days of the week are busier than others, so we prepare our system to handle more passengers. During peak holiday rushes, every available train is on the track," White says. Closed circuit television monitors all stations. If trains are not able to handle all those waiting to board, a controller calls for additional trains to service that area. The controller also communicates directly with waiting travelers over the public address system to let them know that additional trains are on the way. Matching trains to traffic flow is a careful balance that saves the airport thousands of dollars a year in maintenance charges. "There is a direct correlation between miles and maintenance for any train system," says White. "Every mile we can save means reduced charges for labor and parts." The long-term reliability and performance of the transit monitoring system also reduces expenses. An adept in-house programming staff and reliable computing platform combine to save the airport hundreds of thousands of dollars. "We have seen other older transit systems outlay millions of dollars to upgrade equipment, while we spend only $250,000 for equipment we will use for 10 or even 20 years," says White. This kind of fiscal responsibility is practiced throughout airport operations. Operating costs are at the lowest level in 10 years. As a result, landing fees and terminal rents have been lowered. At the same time, revenues continue to rise as a new runway paves the way for growth in passenger and cargo traffic and newly negotiated contracts take effect. In this favorable climate, there are few that doubt that this airport will be the world's busiest by the start of the next millennium.
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