Dynamic traffic management and information is used by road operators in order to improve network utilisation, safety or the environment. Examples are influencing the traffic flow by influencing speeds, lane use, route choice or merging operations by employing variable message signs (VMS), Dynamic Route Information Panels (DRIPs), ramp metering etc. In order to operate the measures, to generate traffic information and to choose the best suitable measure, traffic data are required. Accurate, reliable, high quality traffic data is a prerequisite for effective traffic management and information services. Different data sources are available, such as loop detector data, floating car data (FCD) from GPS or GSM, blue tooth etc. Each data type has its own characteristics and quality. The required quality for a dynamic traffic management (DTM) measure or traffic information service differs, depending on the type of measure or information needed. Some measures are more time critical than others, while also the required accuracy requirements may differ. However, good research to establish requirements for the quality of traffic data in relation to the intended traffic management goals is lacking, while more and more new traffic data is coming available and the demand for reliable traffic information is increasing. Therefore more research on this subject is needed. In this paper, the relation between the accuracy of traffic counts and the effect on route choice and resulting delays is studied. A queuing model is used to calculate queue lengths and delays on two route alternatives, with and without errors on the traffic counts. On a DRIP, the delays over both alternatives are shown, such that a certain fraction of the traffic will change its route choice. This study will show how sensitive this route choice and the effect on the traffic performance is for errors on the input data.