PORTAL Data Quality Analysis

Understanding the data and data quality in the PORTAL transportation data archive is important to maintaining a high quality data archive. This report presents an initial study of the quality of the Oregon Department of Transportation (ODOT) data that is received by PORTAL. We examine the data to attempt to identify trends in the data that may point to issues with the freeway loop detectors and the ATMS system. Summary of Results This report presents an initial high-level analysis of quality of the loop detector data received by PORTAL, the regional transportation data archive which is housed at Portland State University (PSU). The report analyzes data received by PORTAL during the month of September 2008 to identify high-level data quality concerns. The purpose of this analysis is to detect large scale problems with invalid readings or incorrect data reporting; more detailed analysis is required to fully understand detailed data quality issues. This report focuses on four categories of readings: No Traffic, Zero Occupancy, Very High Speeds and Low Overnight Speeds. We reach the following conclusions: • No Traffic. In September 2008, 16% of the readings indicated no traffic was observed at the detector. The analysis indicates that the majority of the no traffic readings likely reflect actual no traffic conditions. However, it does appear that the activation of the SWARM system is causing a slight increase in no traffic readings during the afternoon; these afternoon no traffic readings are likely communication failures due to increased network congestion from SWARM. o Action: PSU will leave no traffic readings as is and assume those readings are valid. ODOT may wish to investigate the impact of SWARM on the afternoon no traffic readings.