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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.
