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68 when a bus stops twice at the same stop, is jockeying around terminal area. When route terminals are located in zones with at a layover, or holds (to avoid running early) away from a poor GPS reception (downtown or a covered terminal), data stop. NJ Transit is interested in using frequent interstop from supplemental devices and logic to interpret it are espe- records for improving maintenance management by correlat- cially valuable. ing operations measures with maintenance needs, particu- larly if future generations of its data collection system can 10.3 Devices to Include integrate data from the vehicle drivetrain system. Integrating other devices in an AVL or APC system can add value either because the data those devices provide is inher- 10.2.4 Arrival/Departure Time Accuracy ently valuable or because of synergies that make the new data AVL systems vary widely in the data captured with respect helpful for interpreting other AVL data. to arrival and departure time at stops and timepoints. Some Door sensors have already been mentioned for their value off-line analyses need arrival time, some departure time, and to help match location, determine arrival and departure some both. Therefore, an AVL system will be more valuable if times, and identify control time. APC systems virtually always it detects and records both arrivals and departures. Door sen- include door sensors; their inclusion in AVL systems would be sors and the recording of door open and close events help a benefit as well. improve the accuracy of arrival and departure detection as Odometer (transmission) data is helpful for determining well. For example, suppose a bus stops two or more times in bus speed, which can be valuable in its own right, and can the neighborhood of a stop. Was the first the stop and the sec- be used to determine when a bus departs from a stop and ond simply traffic delay, or was it the reverse? Or did the bus when/where buses are delayed in traffic. Most AVL systems open it doors both times, so that arrival time should be taken have odometer connections as a backup to GPS or to determine from the first stop and departure time from the second? distance traveled between signposts. Without a door sensor, arrival is frequently detected by a Gyroscopes add richness to the data provided by odome- vehicle entering a 10-m radius zone around a stop. Around ters, allowing vehicles to be tracked off route and permitting major stops and terminals, the zone can be quite a bit larger, matching based on turning locations. which can distort arrival time if a bus faces congestion getting Recording fare transactions in the AVL data stream is a to the stop (e.g., because a traffic queue or another bus is block- means of getting location-stamped boarding data, which can ing the stop). Likewise, zonal detection can distort departure be especially valuable to a transit system lacking APCs. When time if departing buses encounter congestion before leaving the payment medium is electronic and therefore offers an ID the stop zone, which can happen at near-side stops, at stops unique to the passenger, location-stamped fare transaction where buses have to await a gap or yield to crossing pedestrians data offers the further opportunity for inferring link-trip and before entering the traffic stream, and at terminals. transfer information. However, there has been little experi- Knowing both when doors close and when the bus actually ence to date with location-stamped fare records; this area has departs is valuable for detecting holding, which is important considerable opportunity for research and development. for running time analysis. Because of the possibility of hold- Integrating the radio system's control head offers the ing, door close events are not sufficient to determine depar- opportunity to capture records of sign-in data, valuable ture time. Therefore, while door sensors are valuable, they are for matching, and of operator-observed or -initiated events not sufficient. (In many Latin American cities, where buses including pass-ups, special passengers (e.g., wheelchair and routinely operate with doors open, they are almost useless.) bicycle users, fare evaders), and traffic events (e.g., draw- bridge up). These event records provide data that is valuable in its own right for direct analysis. Such records can also add 10.2.5 Route Endpoint Identification detail and accuracy matching to running time and service As mentioned earlier, many AVL systems are weak in deter- analyses, for example, by helping to confirm and perhaps mining when a bus arrives and departs a route terminal. For explain long delays or indicating when the "everybody running time and schedule adherence analyses, these data boards the first bus" assumption behind waiting time calcu- items are critical, and system features that make their correct lations is violated. While radio-based systems always benefit identification easier are valuable. Such system features include from this connection, it would also benefit passenger count- door open and close records, frequent interstop records in ter- ing and event recording systems. Also of potential value, but minal regions, odometer-based records to supplement GPS- not yet applied (to the researchers' knowledge), would be based records in terminal regions, and better algorithms for coded records of standard radio messages initiated by the interpreting bus movements in terminal areas in order to bet- control center, such as instructions to hold for a connecting ter distinguish genuine departures from movements within a passenger.