A method is disclosed for developing traffic messages. The method obtains traffic data indicating collected traffic speeds at various locations on a road network. Traffic messages are developed from the traffic data. The method obtains ground truth data indicating ground truth speeds at a subset of the locations on the road network. The ground truth speed represents average speed of vehicles at one of the locations. For those locations for which ground truth speed has been obtained, the method computes a traffic quality value comparing the collected traffic speed to the ground truth speed for the location. The traffic messages and traffic quality data representative of the traffic quality values are transmitted.