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21 CHAPTER 3 Integrating Other Devices While automatic vehicle location, automatic passenger Since the mid-1990s, the trend has been for APCs to become counting, and farebox systems began as the single-purpose simply a component in a larger data collection system that systems their names imply, their value as data collection sys- includes automatic vehicle location. Location and stop match- tems soon became apparent. Using the expanded definition ing is the duty of the vehicle location system, which operates of AVL as an automatic data collection system that includes out of a main on-board computer called the "vehicle logic location measurement, this section describes other devices unit." The passenger counter includes sensors and a dedicated that can be integrated into the data collection system. on-board computer called an APC analyzer that converts sensor information into passenger counts. Each time the bus leaves a stop, the APC analyzer closes out a record and trans- 3.1 Automatic Passenger Counters mits its on-off counts to the vehicle logic unit. From there, the Unlike AVL, APCs have always been designed with archived data is treated like data from any other device in the data col- data in mind. Valuable reviews of the history of APCs are lection system--either stored on board for later upload, or found in reports by Levy and Lawrence (17), Boyle (14), and transmitted by radio in a stop event message. Friedman (18). APCs use a variety of technologies for count- By integrating APCs into an AVL system, the marginal cost ing passengers, including pressure-sensitive mats, horizontal of passenger counting drops dramatically. Tri-Met, already beams, and overhead infrared sensing. Automatic passenger committed to fleetwide AVL and using one of the simpler APC counting has not yet seen widespread adoption primarily designs, finds the marginal cost of adding passenger counting because of its cost and the maintenance burden it adds. Where to be in the range of $1,000 to $3,000, versus unit costs of adopted, APCs are typically installed on 10% to 15% of the $5,000 to $10,000 often cited for stand-alone systems. This fleet. Equipped buses are rotated around the system to provide marginal cost is low enough that Tri-Met includes APCs in all data on every route. However, technological advances may new coach purchases. With 65% of its fleet already equipped, it is the only large transit system with APC penetration beyond soon make APCs far more common. a small sample of the fleet. Benefits of a large APC sample are The term "APC" can refer to a full data collection system or discussed in Section 10.4. to simply the passenger counter as a device within a larger APC counting accuracy depends on the technology used, data collection system. Historically, APCs were implemented the care used in mounting and maintaining sensors, and algo- as full, independent systems that included location measure- rithms used to convert sensor data into counts. The accuracy ment and stop matching. In spite of the emphasis their name of finished counts also depends on the effectiveness of stop gives to passenger use data, they not only counted passengers matching and identifying the end of the line, subjects discussed but also provided valuable operation data that supported earlier; it also depends on algorithms used for screening, pars- analysis of running time and schedule adherence; in effect, ing, and balancing, which are covered in Chapter 8. they doubled as (non-real-time) AVL systems. Canadian tran- sit agencies have been particularly active in exploiting APC 3.2 Odometer data. OC Transpo, the Toronto Transit Commission, Winnipeg (Transmission Sensors) Transit, Tri-Met, and King County Metro are among the agen- cies that have long benefited from routine reports on passen- As mentioned earlier, all buses have electronic transmis- ger loads, running time distribution, and on-time performance sion sensors that serve as odometers, giving a pulse for every from APC systems. axle rotation. Integrating the transmission into an automatic