A method of and a system for time-dependent route planning

Disclosed is a traffic monitoring system and a corresponding method, involving: generating a database of historical time-dependent traffic speeds or transit times for route segments in a map database for each of a plurality of time windows; identifying currently congested route segments on which the current traffic speed or transit time is less than expected; and predicting a traffic speed or transit time for a future time for a currently congested route segment based on a comparison of recently observed traffic speeds or transit times for the route segment with the historical average traffic speed or transit time for the appropriate time window, said prediction comprising decaying the recently observed traffic speeds or transit times to the historical average traffic speed or transit time as the distance of the prediction into the future grows.