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22 data collection system provides the basis for dead reckoning plained anomalies. For example, one would expect that people and enables data on speed to be captured. Estimating speed transferring from one route to another (the farebox transaction from GPS measurements is not reliable (except over substan- data includes route transferred from) would board the second tial distances) because of random measurement errors. There- bus where the two routes intersect, providing a means of ver- fore, odometer input is preferred to determine when a bus's ifying a stop matching; however, the data shows such trans- wheels start rolling after serving a stop. fers occurring at multiple stops, some a good distance from Some AVL systems also integrate a gyroscope, which indi- the transfer point. Because farebox data is not usually analyzed cates changes in heading. Gyroscope readings will support off- at this level of detail, its quality in many respects has not mat- route dead reckoning and can aid in matching because they tered before. Improving the quality of farebox data will be a detect turns. challenge to efforts to integrate it with AVL-APC data. Once this challenge is met, however, it offers the prospect of a rich data source from 100% of the fleet. 3.3 Door Switch While fareboxes cannot directly measure load because they APC systems in North America always include door switches do not register passengers both boarding and alighting, there to help determine when a bus is making a stop. Even when a are methods of estimating load based on the historical sym- system does not include passenger counting, door switches metry between the boardings pattern in one direction and the can be a valuable means of location matching. If a system alightings pattern in the opposite direction (19). As contact- repeatedly shows doors opening at a location not coded in the less smart cards penetrate the market, card readers, some day, base map as a stop, that information can be used to update the may be able to count passengers alighting as well as boarding. base map. In some Dutch transit systems, door sensors are used Transaction data in which the fare medium is electronic to distinguish time spent holding (bus is resting at a stop, ahead offers the possibility of tracking linked trips and analyzing of schedule, doors closed) from dwell time spent serving pas- transfers, by linking records with a common user ID. Know- senger movements. ing the pattern of where and when a particular farecard was APC vendors in Latin America know that buses there often used to enter the system allows estimation of the cardholder's operate with doors open, rendering door switch readings trip pattern to be made, based on round trip symmetry. The useless. viability of this approach has been demonstrated in the New York subway system (20) and in the multimodal Helsinki tran- sit system (21). A research project is currently under way, with 3.4 Fare Collection Devices promising results, using Dublin bus data in which farecard The traditional electronic farebox has limited data storage transactions are all station stamped. capacity, creating one record per one-way trip with simply a In the near future, Metro Transit plans to introduce smart count of the trip's boardings and revenue. Farebox manufac- cards, bypassing the farebox, with smart card readers inte- grated into its vehicle location system. This arrangement may turers have historically been reluctant to allow their machines finally produce the long hoped-for benefits of integrating fare to communicate with other on-board devices, citing the need to collection with vehicle location. prevent fraud by keeping revenue-related information secure. Limited integration schemes, such as sharing a common oper- ator log-in and interface to the destination sign (to indicate 3.5 Other Devices change in route/direction), have been applied at a few transit 3.5.1 Radio Control Head agencies. Recent products advertise J1708 compatibility (see Section 3.6). As discussed in Section 2.2.1, integrating the control head A new development is the transactional farebox, which ensures that the AVL data stream gets both sign-in data and produces a time-stamped record for each transaction. If the data messages sent by the bus operator to the control center. fareboxes are networked to a smart bus system, transaction data can be transmitted along the data bus and collected as 3.5.2 Passenger Information Systems part of the AVL event stream. If fareboxes are not integrated, off-line integration of the Passenger information devices, including the destination farebox's own data stream with archived AVL data, in princi- sign and next stop announcements, can be integrated with a ple, should be possible, with matching performed on the basis location system; however, because they become consumers, of vehicle ID and time. A research project for the CTA attempt- not suppliers, of information, they add nothing directly to a ing to prove this concept found several obstacles to integrating data archive. Their integration does bring an indirect benefit the data sources. Farebox and AVL clocks were not synchro- to archived data by increasing the pressure for the system to nized. Also, the fare transaction data contained many unex- match routes and stops accurately.