Cleansing of probe car data to determine trip OD

GPS is increasingly being used to collect travel data as the cost of the equipment is relatively low and it is capable of providing continuous and accurate spatial information and speed in real time. One such example is the Internet Protocol probe car (IPCar) project in Japan which equipped probe cars (consisting of taxis and buses) with GPS. The aim of this project is to explore feasible real time applications of IPCar data either as a stand alone data source or with other data sources such as detector counts and automatic vehicle identification (AVI) travel time. The initial focus of this project is to provide travel time information.This study focuses on a data cleansing procedure consisting of 6 steps to determine the OD pattern of the probes. The cleansing process addresses data errors and searches for trip ends and the results show that the cleansed data was accurate in terms of trip length distribution, in particular for trips of more than 1km. The probe data also matched 76%-83% of the trips from an independent data from a taxi management system. The OD pattern gives a macroscopic view of the taxi movement and shows that the main generator and attractor of trips are areas around Sakuragi-cho, Yokohama station, Honmoku, Negishi station and Totsuka. The OD pattern and desired line of the probe car also demonstrate that using taxis as probe vehicles only generate intense data for the small areas heavily serviced by taxis and therefore travel time at a higher level of confidence can only be predicted for these small areas. Future full scale implementation of the IPCar project may need to consider private cars and other sources of information such as detectors and AVI data, to supplement area with sparse taxi coverage.