System for determining the average time taken by vehicles to travel along a road section, comprising: - a plurality of peripheral units (12, 14) distributed along a road network, for detecting an identification code of an on-board apparatus of a vehicle and the moment of transit passing said unit (12, 14), said peripheral units (12, 14) comprising units installed on gates at automatic toll collection stations and units installed in transit at predetermined locations along the road section, the data recording the transit of a same vehicle at two separate peripheral units (12, 14) being associated on the basis of the single identification code of the on-board apparatus of the vehicle; - and a central processing unit to which said peripheral units (12, 14) are connected, adapted to: - determine a time interval for monitoring a road section; - determining, for each identification code having associated therewith two moments of transit detected at two different peripheral units (12, 14) during a predetermined travel interval, the travel time of the associated vehicle between said units (12, 14) as the difference between the moments of transit detected; - compare the number of vehicles recorded in said predetermined time interval by the peripheral units (12, 14) which define a road section, with a predetermined minimum threshold number; and - if the number of vehicles recorded by said peripheral units (12, 14) is greater than said predetermined minimum threshold number, determine the average travel time of the road section situated between said peripheral units (12, 14) on the basis of the average travel time of the plurality of vehicles which have travelled along said section within the predetermined time interval, wherein each peripheral unit (12, 14) comprises a time synchronization module, and wherein the central processing unit is interfaced, through communication means, with a module for the control of information messages intended for variable-message panels, a system for translation of road traffic events into DATEX language, at least one client system adapted to display a summary synoptic panel of the state of the network in terms of average travel times, together with a list of road sections in an alarm condition if the average travel time exceeds a predetermined threshold for the road section. - a plurality of peripheral units (12, 14) distributed along a road network, for detecting an identification code of an on-board apparatus of a vehicle and the moment of transit passing said unit (12, 14), said peripheral units (12, 14) comprising units installed on gates at automatic toll collection stations and units installed in transit at predetermined locations along the road section, the data recording the transit of a same vehicle at two separate peripheral units (12, 14) being associated on the basis of the single identification code of the on-board apparatus of the vehicle; - and a central processing unit to which said peripheral units (12, 14) are connected, adapted to: - determine a time interval for monitoring a road section; - determining, for each identification code having associated therewith two moments of transit detected at two different peripheral units (12, 14) during a predetermined travel interval, the travel time of the associated vehicle between said units (12, 14) as the difference between the moments of transit detected; - compare the number of vehicles recorded in said predetermined time interval by the peripheral units (12, 14) which define a road section, with a predetermined minimum threshold number; and - if the number of vehicles recorded by said peripheral units (12, 14) is greater than said predetermined minimum threshold number, determine the average travel time of the road section situated between said peripheral units (12, 14) on the basis of the average travel time of the plurality of vehicles which have travelled along said section within the predetermined time interval,