A road traffic monitoring system includes: a first input for receiving position estimations of mobile terminals; a second input for receiving input specifications chosen depending on the type of service for which such monitoring is performed; and an output for generating road traffic maps, each road traffic map being associated with a set of territory elements and including, for each one of the territory elements, at least one mobility index of mobile terminals travelling within such territory element. Preferably, input specifications are chosen among at least two of the following parameters, territory element, territory element observation time slot, and maximum allowable error on the estimation of at least one mobility index.