United States Department of Transportation
i
Assessing the performance of the SpeedInfo sensor.
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2013-12-01
[PDF-15.05 MB]
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Abstract:Until 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.
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