School of Architecture and Civil Engineering

Investigation of traffic flow at driveways of plan-free intersections of road category group A - A contribution to the dimensioning of the driveway opening.


Against the background of a constant increase in traffic density and speed on federal highways (BAB) as well as an increasing densification of the BAB network, traffic flows on federal highways are becoming more and more complex. As a result of these changes in the external demand factors, the behavior of road users has also changed. The forthcoming investments to supplement or, in the eastern federal states, to expand the BAB network require a secure basis for dimensioning the roads to be planned. There is considerable potential for savings in the dimensioning and design of intersections, among other things. In order to be able to assess the effects of a reduction in the standard of the design elements of plan-free intersections, in particular the shortening of the entrance lanes as well as the application of lower design speeds for the entrance ramps, detailed knowledge of the traffic flow in the area of the entrances as a function of the traffic volume and speed level in the entrance ramp and on the main carriageway is necessary.The study concludes, among other things, that the required length of the entrance opening is related to the ramp alignment, which influences the speed level in the entrance ramp, and the traffic volume on the main roadway. With the help of the knowledge of this interaction, it is possible to address site-specific boundary conditions in the design of driveways at grade-separated intersections.Indications of a possible shortening or necessary lengthening of the driveway opening from the dimension of 250 m anchored in the valid guidelines cannot be derived from this study. The comparison of the findings obtained here with results from a more recent investigation at plan-free intersections (category group B) with parallel ramp guidance makes it clear that entry processes are completed considerably earlier at these intersections. The traffic advantages of parallel ramp routing, in conjunction with the lower space requirements and the lower construction costs, indicate that it could possibly also be used on roads in category group A. The results of this study show that parallel ramp routing can be used for traffic management purposes, and that it is easier to find a suitable vehicle gap in the main flow than with curved ramp routing.

This Abstract was translated from German with deepL and could be faulty.

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