  Crowdsourced GPS probe data has been gaining popularity in recent years as a
source for real-time traffic information. Efforts have been made to evaluate
the quality of such data from different perspectives. A quality indicator of
any traffic data source is latency that describes the punctuality of data,
which is critical for real-time operations, emergency response, and traveler
information systems. This paper offers a methodology for measuring the probe
data latency, with respect to a selected reference source. Although Bluetooth
re-identification data is used as the reference source, the methodology can be
applied to any other ground-truth data source of choice (i.e. Automatic License
Plate Readers, Electronic Toll Tag). The core of the methodology is a maximum
pattern matching algorithm that works with three different fitness objectives.
To test the methodology, sample field reference data were collected on multiple
freeways segments for a two-week period using portable Bluetooth sensors as
ground-truth. Equivalent GPS probe data was obtained from a private vendor, and
its latency was evaluated. Latency at different times of the day, the impact of
road segmentation scheme on latency, and sensitivity of the latency to both
speed slowdown, and recovery from slowdown episodes are also discussed.
