Abstract The Portland Oregon Regional Transportation Archive Listing (PORTAL) is the official intelligent transportation systems data archive for the Portland metropolitan region. PORTAL has been archiving 20-second speed, count, and occupancy data from the approximately 500 inductive loop detectors in the Portland metropolitan region since July With a web-based interface, PORTAL provides performance metrics designed to assist practitioners and researchers. In order to provide accurate and useful information, it is essential that PORTAL process and maintain high-quality data, and further it is critical that users understand exactly how the data are processed. Users should also have a clear understanding of the quality of the data that they are viewing or extracting. There are several elements involved in maintaining quality data: effective allocation of maintenance resources for the inductive loop detectors, identification of suspect data values, and proper data aggregation. This paper presents a methodology for automatically detecting malfunctioning inductive loop detectors; describes how suspect data values are detected, handled, and reported in PORTAL; and finally describes PORTAL’s data aggregation procedures. Examples of tools used to communicate data quality to PORTAL users are also provided. Conclusions This paper describes the measures PORTAL uses to improve and maintain the quality of the data in its archive. Automatic detection of malfunctioning detectors and a monthly report to ODOT listing the detectors most in need of maintenance have been described. Detection of malfunctioning detectors focuses on detector configuration errors and communication errors. Initial reports on detector malfunctions have been provided to ODOT and PSU is awaiting feedback from ODOT. This feedback will be used to improve the data quality tests. Methods for detecting suspicious data values as well as aggregation and performance measure calculations in PORTAL are described in detail as well as the availability of new data quality information to PORTAL users. The reports and procedures described in this paper form the basis for the PORTAL data quality process; this process will evolve and improve as the effects of the detector maintenance and data quality process are observed. Acknowledgements The authors would like to thank the National Science Foundation for funding this research. The authors gratefully acknowledge the Oregon Department of Transportation and, in particular, would like to thank Dennis Mitchell and Jack Marchant for their contributions to the project.  Automatic Detection of Malfunctioning Loop Detectors  Inductive loop detectors need regular maintenance to perform well  Important to allocate sparse maintenance resources well  Procedures for automatically determining which detectors are most in need of maintenance  Focus on two categories of errors: detector configuration and communication failure  Portal Data Cleaning, Data Quality Display and Aggregation  Set of data quality flags to flag suspicious readings  20-second data values are flagged as suspicious if they fail any of a set of tests  Aggregate non-flagged data into 5-, 15- and 20-min intervals (count, speed, occupancy, VMT, VHT, delay, travel time)  Data quality display in portal – indicate quickly and graphically to the user how a detector performed over a particular time interval Stations Reporting:  No Traffic (all lanes) > 20% of Samples  OR Communications Failure > 15% of Samples Data from weekdays in June 2006.

(a) 1011; I-5 N Stafford Rd; Lane 3 (b) 1204; I-5 N Denver Ave; Lane 2 (c) 1212; I-5 N Delta Park; Lane 2 (d) 1244; I-5 S Swift Blvd; Lane 1 (e) 1481; I-84 W 33rd; Lane 2 (f) 1695; US 26 W Skyline Rd; Lane 3 (g) 1123; I-5 N Multnomah; Lane 3 (h) 1637; US 26 E 185th Ave; Lane 2 (i) 1787; I-205 N Ore 43; Lane 2 Toward the Systematic Improvement of Data Quality in the Portland, Oregon Regional Transportation Archive Listing Dr. Kristin Tufte, Dr. Robert Bertini and James Rucker, Portland State University Dr. Soyoung Ahn, Arizona State University Benjamin Auffray, L'école nationale des travaux publics d'Etat Toward the Systematic Improvement of Data Quality in the Portland, Oregon Regional Transportation Archive Listing Dr. Kristin Tufte, Dr. Robert Bertini and James Rucker, Portland State University Dr. Soyoung Ahn, Arizona State University Benjamin Auffray, L'école nationale des travaux publics d'Etat Number of Samples Failing Selected Conditions; January-June 2006; highway I-5 Flow-occupancy plots for sample detectors; July 26, 2006–July, (M-F) DetectorIdLocationMilepostLane NumStationIdTests FailedAction 1011I-5 N Stafford Rd WB to NB Low avg occ 1244I-5 S Swift Blvd/Marine Dr SB Speed < I-5 N Multnomah Blvd NB Occ > 95, Speed < I-5 N Denver Ave NB Low max occ, Low avg occ 1205I-5 N Denver Ave NB Low avg occ 1206I-5 N Denver Ave NB HOV Low avg occ 1212I-5 N Delta Park NB Low max occ, Low avg occ 1695US 26 West Skyline Rd WB Occ > US 26 East 185th Ave SB to EB Occ > I-205 North Ore 43 NB-NB Low avg occ 1481I-84 West 33rd WB Speed < 5 Sample Monthly Configuration Errors Report (Partial June 2006) ConditionThreshold LowMediumHigh High percentage communication failure during peaks 5% of samples15% of samples30% of samples May 06June 06May 06June 06May 06June 06 Number (percent) of Failing Detectors 19 (5%)27 (8%)12 (3%)22 (6%)9 (3%)8 (2%) High percentage no traffic samples during peaks 10% of samples20% of samples55% of samples May 06June 06May 06June 06May 06June 06 Number (percent) of Failing Detectors 46 (13%)49 (14%)38 (11%)36 (10%)6 (2%) Communication Tests: Conditions, Thresholds, and Number (Percent) Failing Detectors Display of monthly and daily data quality information in PORTAL (July 2006) StationIdLocationMilepostTests FailedAction 1020I-5 N 1188 Alberta St NB304.40Comm Failure 1038I-5 S Upper Boones SB291.25Comm Failure 1094US 26 West Cedar Hills SB to WB68.20Comm Failure 1013I-5 N Terwilliger Blvd NB297.33Comm Failure 1135Broadway to I-405 SB1.08No Traffic 1110I-205 N Ore 43 NB-NB9.03No Traffic 1134I-405 S 5th to I-405 SB0.97No Traffic 1130I-5 S Lombard EB to SB305.40No Traffic Sample Communication Failures Report (Partial June 2006) ConditionLow ThresholdMedium ThresholdHigh Threshold Count > 171% of samples0.3 % of samples0.2% of samples Occupancy > 95%5% of samples0.5% of samples0.25% of samples Speed > 100 MPH5% of samples1% of samples0.5% of samples Speed < 5 MPH30% of samples10% of samples5% of samples Low Max OccupancyMax Occupancy = 0Max Occupancy < 20Max Occupancy < 25 Low Average Occupancy Peaks Average Occupancy < 4% Average Occupancy < 5% Average occupancy < 6% Detector Configuration Tests: Conditions and Thresholds ConditionLow ThresholdMedium ThresholdHigh Threshold May 06June 06May 06June 06May 06June 06 Volume > 1714 (4%)18 (5%) 5 (1%)12 (3%)2 (1%)0 (0%) Occupancy > 95%26 (7%)26 (8%)15 (4%)17 (5%)7 (2%) Speed > 100 MPH15 (4%) 7 (2%) 1 (0%) Speed < 5 MPH36 (10%) 27 (8%)22 (6%)9 (3%)11 (3%) Low max occupancy25 (7%)28 (8%)11 (3%)10 (3%)8 (2%)7 (2%) Low average occupancy peaks 34 (10%)36 (10%)22 (6%) 14 (4%) May-June 2006 weekday peaks 7-9 AM and 4-6 PM Number of Detectors Failing Tests at Various Threshold Levels Monthly Data Quality I-5 N at Multnomah lane 3 (July 2006) Daily Data Quality I-205 SB at Division all lanes (July 13, 2006)