Trip matching

Vehicle movements must be measured and recorded by an on-board system or by an Automatic Vehicle Location (AVL) system. This data must subsequently (or in real-time) be matched with the scheduled trips. Some systems use GPS, other use beacons along the route, still others use an odometer signal, many use a combination of these.

This matching operation is hard to do correctly. The quality of this operation is vital to the usability of the results in TRITAPT (or any other system). We have seen really weird problems when matching observed trip data with scheduled data. The table below may be useful for finding faults in similar systems.

Observed problem	Possible causes
Rediculous dates and/or times in recorded events	Failing real-time clock or battery.
Vehicles (apparently) travel back in time	Failing real-time clock
Vehicles (apparently) drove forward or backward by some multiple of approximately 32 km (this is the value that we observed in our case) without recording a single event	Memory errors in the on-board computer
Vehicles that exceed the maximum speed limit for short distances by an impressive value	GPS or odometer errors
Odometer values do not change	Odometer sensor or cable failure
Recorded odometer values are off by a few percent	Odometer calibration was not carried out for a long time (and tires have worn), or odometer calibration not carried out after replacing tire(s)
Recorded odometer values are off by a factor of 2	Error in odometer catlibration
Beacons detected that should not be on the route	Wrongly programmed beacon transmitters
Inconsistencies in trips that run past midnight	Buggy trip matching software
Impossible dates	Failing battery of real time clock
Vehicles that never seem to open their doors	Defective door switch
Vehicles with huge imbalance between boarding and alighting passengers	Failing, or wrongly installed passenger counting equipment on some of the doors
Vehicles that follow most of the scheduled route but deviate from it shortly before the end of the last trip of a shift	Vehicle was empty and driver / operator decided to not drive the empty vehicle all the way to the terminal stop
Vehicles that depart early from the initial stop but somewhere before the next stop wait a long time	AVL system mis-identifies departure from initial stop
Missing stops, route deviations	Detour due to road construction work that was not coded in the schedule
No trips recognized on a route	Beacon defective, changed, detour due to construction work, trips temporarily carried out with buses hired from another company
No trips recognized from a particular vehicle	AVL or communication failure with the on-board equipment

TRITAPT has been used to identify and fix a variety of problems in existing AVL, board computer and trip matching systems. Quite often, we have found that there were several problems, but one of these generated so many errors and warnings that it had to be fixed before the next problem became even noticable.

We have developed software that matches trips for a variety of environments. We do not consider this part of the TRITAPT system, but we can certainly help with the development and improvement of trip matching software. Our trip matching software is written in ANSI-C and/or PERL and runs under Linux, MS-DOS, Windows 95, Windows 98, Windows XP, Vista, Windows 7 and probably anything else that is somewhat POSIX compliant.

Besides production of the data files, this phase can also produce daily performance indicators that can be made accessible on web pages. Such web pages have been used to identify recurrent problems in on-board equipment and problems that were related to a particular group of vehicles in a fleet. Equipment in the field fails often and a good monitoring system is required to keep things working satisfactorily.