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CATT validates probe travel time data on low-volume roads in MD 

CATT validates probe travel time data on low-volume roads in MD 

Travel time and speed data acquired through the Eastern Transportation Coalition’s Vehicle Probe Project (VPP) Marketplace are widely used by transportation agencies to inform traffic operations and planning decisions.  CATT researchers are responsible for independently evaluating the commercial probe data by regularly spot-checking vendor data accuracy on a variety of road types and geographic areas – a process that involves collecting field travel time measurements to represent ground truth conditions.
Previous validation studies have primarily emphasized freeways and signalized arterial facilities that carry mid-to-high traffic volumes. Probe-based speed and travel time data have been proven an effective representative along freeways and many high-volume arterials, with arterial data quality showing noticeable improvement over the past few years.   As such, the CATT validation team has recently turned its attention to an evaluation scenario that has been under-represented in previous studies:  low-volume facilities.
Probe data was recently evaluated in Maryland, focusing on low-volume corridors chosen in collaboration with Maryland State Highway Administration: MD-30 near the MD-PA border, and US-11 and US-40 in Hagerstown.  In addition to conducting the operations-focused data validation approach that measures contract compliance, the CATT validation team introduced an additional methodology to evaluate vendors’ ability to capture recurring, time-of-day patterns – an approach oriented towards arterial management and planning applications that is well-suited for low-volume conditions.  The resulting report was recently published online, and includes the following top-level findings:
Operations perspective
  • There were fewer opportunities to evaluate vendor data from an operations-focused, “point-in-time” perspective due to low sample size in the reference data, but all three vendors provided speed and travel time data that were in line with contract expectations. 
Planning / arterial management perspective
  • Median vendor and reference travel time values matched well for most time-of day periods, indicating that the data would likely be useful for planning applications that require accurate “typical” travel time (or speed) values. 
  • Whenever there was significant variation in travel times during a time-of-day period, the vendors usually under-reported variation compared to the reference data (i.e., overestimated travel time reliability). However, this appears to be primarily an artifact of how probe data is delivered (1-minute average travel time records) rather than a data quality issue.
This report, as well as previous validation reports, whitepapers, and presentations, can be found on the ETC VPP Marketplace website (link) under the data validation tab.  Please contact Zach Vander Laan ( for further questions. 

March 4, 2021

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