The introduction of GPS technology in buses can overcome this difficulty in terms of information availability, although it presents the challenge of processing huge amounts of data in a systematic way. Here, we present a method based on GPS-generated data to systematically monitor average commercial bus speeds. The framework can be applied to each bus route as a whole, as well as over segments of arbitrary length, and can be divided into time intervals of arbitrary duration. The results are presented as matrices and graphs that can be read and interpreted easily. We discuss the potential of this methodology to provide useful insights for bus system planners and operators. The method and its applications are illustrated with data coming from the Santiago–Chile public transport system (Transantiago), where GPS observations of more than 6000 buses operating on over 700 different routes are available every 30 s.