Assessing the performance of the SpeedInfo sensor

"Prepared in cooperation with the Ohio Department of Transportation and the U.S. Department of Transportation, Federal Highway Administration."; "December 2013.; Includes bibliographical references (page 33).; Final report.; Text document in PDF format.; Performed by Ohio State University, sponsored by Ohio Department of Transportation; Harvested from the web on 3/5/14Until recently freeway traffic operations data were collected in house by the Ohio Department of Transportation (ODOT) using loop detectors. In recent years several private companies have emerged with a viable opportunity to outsource traffic data collection. While these new business models and ease of deployment are compelling, there are few published studies explicitly evaluating their performance. ODOT has contracted with two of these data providers: SpeedInfo and INRIX. This study exploited a unique juncture as ODOT transitioned to the new third party data collection: the two new systems and the legacy loop detectors were concurrently operational in Columbus, OH for approximately 6 months. Using the archived data from this period, we evaluated SpeedInfo and INRIX performance over a 14 mi. This long period of time ensured that we would have a better chance of observing intermittent features that might go unobserved in a short-term study. Both SpeedInfo and INRIX traffic data generally performed within specifications, exhibiting small biases that could likely be fixed with fine-tuning. Both sensors also exhibited a reporting lag, on the order of 60 sec for SpeedInfo and 360 seconds for INRIX (comparable to conventional 60 sec and 5 min aggregation periods used in loop detectors). Although the lag and bias are within specifications, some applications might be sensitive to them, e.g., traffic responsive ramp metering. Each system also exhibited unique behavior not found in the other. SpeedInfo is sensitive to precipitation: sometimes going offline for tens of minutes. When mounted on the shoulder, SpeedInfo showed slightly degraded performance on the far side traffic. INRIX reported speeds every minute, but after excluding repeated values, the actual effective reporting period was more like 3-5 min, with occasional periods of repeated measurements lasting in excess of 10 min (already reflected in the lag above). INRIX also provides two measures of confidence, neither of which reflects the measurement repetition