United States Department of Transportation
i
Independent Evaluation of a Probe-Based Method to Estimate Annual Average Daily Traffic Volume
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2021-09-11
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[PDF-1.80 MB]
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Edition:Final Report
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Abstract:This report documents an independent evaluation of annual average daily traffic (AADT) estimates developed from traffic probes by StreetLight Data, Inc (StL). The Texas A&M Transportation Institute (TTI) researchers performed a systematic process to identify accurate permanent continuous counter sites maintained by public agencies and private entities that could be used as benchmark sites against which to evaluate these AADT estimates. Ultimately, though, TTI could only use 215 bidirectional (552 directional) continuous count sites owned and maintained by state departments of transportation. TTI researchers used several evaluation measures and several statistical hypothesis tests to assess the accuracy and precision of StreetLight Data’s AADT estimates. These multiple evaluation measures and hypothesis tests produced mixed results. Some statistical tests provided contradictory or counterintuitive results while other statistical hypothesis tests indicated that StL’s AADT estimates are statistically the same as the benchmark AADT values. TTI used professional judgment to weight and consider each evaluation result, and concluded that StL’s AADT estimates are valid for traffic monitoring use on roads with bidirectional AADT of 5,000 or greater vehicles per day. Because the evaluation results were mixed and the validity decision was not clear cut, TTI recommends phased implementation that includes two elements: 1) a one-to-three year transition period (DOTs still collecting short duration counts but comparing to StL AADT estimates) should be used to confirm TTI's professional judgment based on these mixed evaluation results; 2) a pilot implementation program initiated by FHWA that includes up to five early adopter state DOTs, to monitor and coordinate findings in early-adopting states.
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