The invention relates to a method for predicting the traffic flow in a road network. Sensors in the road network register the passage of vehicles and two of the parameters, flow, density, speed enable all three parameters to be calculated. The correlation between the traffic at a point X at a certain time and the traffic at another point Y some period .tau. later can in certain cases and under certain conditions provide good values. In these cases, the traffic can also be predicted with good precision. The invention utilizes this fact and relates the prediction factor to the correlation coefficient. The invention also uses the methods to divide a traffic parameter into various frequency components to be used in various situations and improves the prediction by using the corresponding prediction factor for the corresponding frequency components of the traffic parameters. For the prediction, sensor information from different links is used in some cases to provide a quicker and more effective prediction by means of cooperation. The method for providing this cooperating also belongs to the invention. In certain sensor-lean situations, the prediction factor described previously is supplemented with a propagation factor W that describes the traffic changes along a traffic link, and where W can be defined and adapted to the various frequency components of a traffic parameter.