Travel Time and Reliability: Is Data Quality a Showstopper? The Georgia Navigator Experience Angshuman Guin URS Corporation ITSA Phoenix May, 2005

Overview NaviGAtor Travel Times Data Failure Issues Remedial Measures –Transportation Sensor System (TSS) –Maintenance Management Plan (MMP) Key Stations VDS Quality Assurance

Georgia NaviGAtor’s Video Detection System (VDS)  1,361 Fixed Black & White Cameras  Spaced Every 1/3 mile on Freeways  Continuous Speed / Volume/ Occupancy Data  Generates Travel Times for CMS

Navigator ATMS Archive Data Attributes –Volume / Count –Average Speed (per 15 minutes per lane) –Lane Occupancy (per 15 minutes per lane) Frequency: 20 second data aggregated to 15 minutes data in archive Per Lane Bi-directional Mainline / Ramps

Travel Times on Website

Travel Time Determination Dynamic Message Sign – Trip section is comprised of 2 Zones – Each Zone is comprised of 2 Sub-Zones – Each Sub-Zone is comprised of several Stations x DMS Destination Direction of Travel ZONE 1 ZONE 2 Subzone 1-1 Subzone 1-2 Subzone 2-1 Subzone 2-2

Travel Time Determination cont. Dynamic Message Signs cont. – 20 Second Station average speeds are aggregated into 1 minute Station, Sub-Zone and Zone average speeds – 1 Minute Zone average speeds are categorized as: Moving Very Well (55 + mph) Moving Well (40 – 55 mph) Moving Slowly (30 – 40 mph) Moving Very Slowly (< 30 mph)

Travel Time Determination cont. Dynamic Message Signs cont. – 16 Travel Time messages are created in the message library for each DMS and displayed as traffic conditions change according to the matrix below Message: Travel Time = min Message: Travel Time = 16+ min Message: Travel Time = min

Travel Times as a Performance Measure

Travel Time Variability

Data Failure Issues

Existing Archived Data Flow

Remedial Measures Data Archive – Architecture (Transportation Sensor System – TSS) – Data sample Data Collection (Maintenance Management Plan) – Hardware – Software

TSS Process - Server Administration - Communication

New Navigator Archive XML Format 5-Minute intervals instead of 15-Minute Truck percentages Filtering of data to eliminate bogus data Meta-data information Transportation Sensor System (TSS) Attributes Detector ID (integer) StartTime (datetime) Duration (integer, seconds) Total-volume (integer, 0+) Percent-trucks (float, ) Lane Occupancy (float, ) Average Speed (float, 0.0+) Std. Dev. Lane Occupancy (float, ) Std. Dev. Average Speed (float, 0.0+) VALIDITY (integer ) –Percentage of valid samples in 5-minute aggregate AVAILABILITY (integer ) –Percentage of available samples in 5- minute aggregate

Data Quality Measures: Availability and Validity where: n useable values = the number of data samples with values present in the aggregate n total expected = the total number of data samples expected for the aggregate where: n valid = the number of data samples with values meeting the validity criteria n total expected = the total number of data samples expected for the aggregate

Validity Criteria Lane Occupancy ----> VolumeVolume

Maintenance Management Plan  Hardware Failures  Quality Assurance

Maintenance Management Plan Data calibration and validation with Ground Truth data 1361 VDS Stations (5000+ detectors) Key Stations (20+) Problematic Detector Indicator Methodology

Key Stations & Priority Stations

Problematic Detector Indicator Methodology where: E v : expected value for the station volume, V k : volume of the key station associated with this station, K TOD DOW f :key-station adjustment factor for TOD and DOW, ε : expected error tolerance

Maintenance Management Plan Key Stations (20+) –Maintenance not only for failure but also for data quality Data calibration and validation with Ground Truth data –Formalized procedure –Defined sample requirements –Use Hypothesis Testing (paired-t) –Obtain accuracy statistics

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