This vignette explains the details of the large traffic data set known as UTD19 collected by Allister Loder and Lukas Ambühl from ETH Zurich. The data was first published in https://www.nature.com/articles/s41598-019-51539-5 and is now available on https://utd19.ethz.ch/
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You might also be interested to access more traffic data by our friends @EPFL: https://open-traffic.epfl.ch/ or @GraphHopper: https://github.com/graphhopper/open-traffic-collection