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This paper presents the results of the first large-scale assessment of the service quality of the road network of the Canton Zurich. Three GPS-equipped floating cars were deployed for three weeks on a set of three randomly selected, representative measurement circuits of circa 500 km length. Vehicle coordinates were logged each second for over 2.5 million data records. The experimental approach, data gathering, data reduction, map matching, and speed results are described. A newly developed map matching algorithm is outlined, as particular difficulties with the available GIS network models made the application of commercial software impossible. The results are summarized categorically by type of road, time period and road owner. In addition to the calculation of the standard deviation, an assessment of the measurement error was performed to provide a complete measure of the variability. The main substantive results are the high speeds and large speed variances on the motorways, in contrast to the lower speeds and higher reliability of the minor road network.