The economic planning of roads and traffic management systems for the prevention of congestion demands the exact projection of the existing traffic situation. Means for the assessment of the traffic flow are fundamental diagrams, which are compiled from empirical data of flow, density and speed measurements and which are aggregated to time intervals of constant length. Due to the constant interval length different traffic situations may be included into one time interval of e.g. one hour. For that reason the aggregated traffic flow, traffic density and mean speed do not represent the different traffic situations occurring during that interval. Only within periods of stationary traffic flow, the calculated values of speed, traffic volume or density are constant during the time interval. A fundamental diagram derived from stationary parts of the traffic stream gives a much more reliable description of the quality of traffic flow and capacity than fundamental diagrams usually based on constant time intervals. Therefore a program has been developed to analyse on-line traffic data on stationary parts of the traffic stream and to calculate fundamental diagrams. Measurements of traffic flow situations on German highways have been analysed using this program and results have been obtained in determining the capacity of the relevant highway. Furthermore it has been used for a comparison of fundamental diagrams based on constant intervals with stationary fundamental diagrams. The results can be used for the decision on the aggregation method of traffic data. (A)
Abstract