We at Juno track a massive fleet of taxi cars in a relatively small area of New York. For all the internal mapping we use OpenStreetMap — and we are naturally interested in it having zero road errors. One way to ensure that is to validate it against tens of thousands GPS traces we get every day. In this talk we'll look at the relation of traces and map data in OSM, find a few ways to improve OSM using these traces, and see the validation system we made.