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23 3.5.3 Wheelchair Lift ages traffic on the VAN. Nearly all the relevant devices man- ufactured today comply with the J1708 family of standards Lift sensors can initiate a location-stamped record of lift (23, 24) published by SAE, the integration standard used in use, a valuable piece of information for off-line analysis of many AVL systems. Some AVL integrators use a proprietary both ridership and running time. In the survey, no examples VAN protocol that they claim handles message traffic better. of lift sensors being used in AVL systems were found; lift data, An advantage of integration is providing operators with a where available, came from operator-initiated messages sent single interface and a single sign-in, which can be shared (in by radio. principle) with such disparate devices as the radio, the event recorder (a function usually taken by the vehicle logic unit), 3.5.4 Silent Alarm the farebox, the stop announcer, and the destination sign. In practice, fareboxes are rarely integrated and therefore have a AVL systems usually include an operator-initiated silent separate interface. alarm for emergencies. Its recording is valuable for incident The most significant integration is the integration of APC investigations. with AVL, first implemented in the mid-1990s at Tri-Met. The AVL vendor provided a smart bus with location tracking; 3.5.5 Mechanical Sensors therefore, the APC subcontractor had to provide only the pas- senger sensors and APC analyzer, relying on the AVL system Transit buses have had electronic controls and monitor- for stop matching. Another example is a stop announcement ing systems for many years (22). Besides transmission sen- system vendor who provides the smart bus system, with APCs sors, such systems include, for example, engine heat and oil added as a supplemental device. pressure sensors. AVL systems have sometimes taken input While it may seem obvious that AVL, APC, and stop from such sensors, triggering mechanical alarms for high tem- announcement systems should share location systems and perature or low pressure; however, false positives have been on-board computers, their integration is only a recent devel- too frequent and therefore no use has been found for mechan- opment. In fact, for various cost and contract reasons, sepa- ical alarms. rate location systems are still being installed independently at It has been suggested that mechanical data incorporated some transit agencies that lack the smart bus foundation, with into a data archive (as opposed to triggering real-time alarms) buses having multiple GPS receivers, multiple on-board com- may yield valuable insight into maintenance needs. puters, and, in spite of efforts to avoid it, multiple operator interfaces. Using an open, standards-based smart bus design 3.6 Integration and Standards when procuring an AVL, APC, stop announcement, or event recording system substantially lowers the marginal cost of On-board devices can be integrated in an ad hoc fashion, or adding the other functions and provides flexibility for later following a systematic integration standard. Standardization procurements. helps promote the cost and efficiency benefits of modularity and re-use. 3.6.2 Other Integration and Standards Efforts 3.6.1 SAE Standards and Smart Bus Design Transit Communications Interface Profiles (TCIP) Systematic on-vehicle integration of devices has been called the "smart bus" concept. The principal on-vehicle device is The TCIP project, started in 1996, is a standards develop- the main data collection computer or vehicle logic unit. In ment effort sponsored by the U.S.DOT's Joint Program Office principle, the vehicle logic unit and other devices are each for Intelligent Transportation Systems (ITS). Its mission has connected to a twisted pair of copper wire running the length been to define the data elements and message sets that can be of the vehicle and called the "data bus." (In practice, there are specified as an open data interface for transit data interchange often a few devices, such as GPS receivers, connected directly activities. Phase 1, completed in 1999, established a transit ITS to the vehicle logic unit instead of via the data bus. Wireless data interface "Framework" and eight "Business Area Object networking has also become possible as a substitute for a phys- Standards." Phase 2, completed in June 2001, built on the work ical data bus.) The network consisting of the data bus and of Phase 1 by developing the transaction sets, application pro- attached devices is a local area network (LAN, often called a files, and guidebooks required to test and implement TCIP. "vehicle area network" (VAN). Devices broadcast messages on Some of the pertinent TCIP developments include the network when triggered by an event; other devices receive or ignore the message, depending on how they are programmed. The definition of automatic vehicle location objects, includ- A communication protocol governs message types and man- ing compass bearing parameter, current time, current date,

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24 trip distance, position, velocity vector, total vehicle distance, ple working to improve the TCIP standard are those involved and milepost identification; with AVL and APC data. The definition of conformance groups that consist of a list of objects required to support a specific function. Confor- Location Referencing Guidebook mance groups were defined for dead reckoning, triangula- tion, GPS, etc.; The recently published Best Practices for Using Geographic The development of a standard on spatial representation Data in Transit: A Location Referencing Guidebook (12), funded objects, including a data dictionary and the definition of jointly by FTA and the Transit Standards Consortium, pro- message objects set; and motes effective practices in the exchange and use of spatial The development of a standard for on-board objects, also data, including stop and route definitions. including a data dictionary and the definition of message objects set. FTA National Transit GIS Initiative TCIP object definitions include most schedule features, The FTA initiated in the mid-1990s a National Transit Geo- which are important for matching a vehicle and data collected graphic Information System to develop an inventory of pub- on it to the route and trip on which it is operating. Some AVL lic transit assets in the United States. Although the effort and APC vendors have adopted the TCIP standard for their focused primarily at a high national level, it was also designed schedule data. However, TCIP has not yet been widely adopted to encourage more use of GIS tools by transit systems. Its by transit agencies as part of their product specifications and 1996 report discusses the design of bus stop and route data- Requests for Proposals. Moreover, there are aspects of sched- bases as well as specifications for data exchange involving ules that are not covered in TCIP, such as when a bus is simul- GIS databases (25). This effort was to some extent a precur- taneously discharging passengers from an inbound trip and sor to the Location Referencing Guidebook project discussed picking up passengers for an outbound trip. Among the peo- earlier.