Presented is a characterization of travel speed on any roadway segment based on probe vehicle position data. Most of the characterization is based position data obtained from GPS receivers because of their high precision and their increasing availability. Comparison is also made to Qualcomm's Automatic Satellite Position Reporting (QASPR) system because of its long history (10+ years) of extensive use by the long-haul trucking industry. Described is the use of these data in conjunction with digital map representations of roadways with particular reference to ALK's digital map database of North America. Two examples of the use of probe vehicle based GPS data to ascertain and monitor speed on roadway segments are presented. One is a demonstration of the monitoring of the speed performance of the various road segments that make up the Québec-Windsor corridor. Extensive GPS data from the first half of 2008 characterize the speed performance of the corridor by day-of-week and time-of-day. The second example also uses GPS probe vehicle data to assign a median speed, by direction, to all 31 million arcs of ALK's digital map database of North America. Examples of that assignment are displayed in geographic bandwidth charts and a generic example of a fastest route computed based on the assigned median speeds is presented.