Currently, the comparatively young floating car technology is mostly used to get information about travel times which however are more attractive to navigation and route guidance. Concerning traffic management applications such as traffic light control, it is more likely to know about exact delay times induced by traffic lights or the queue lengths. So, a new method based on existing floating car systems is developed which in its first version provides estimations of queue lengths at traffic lights. This finally allows for an area-wide urban traffic monitor-ing without any additional infrastructure which is capable for typical traffic management applications.