Generalizing FHWA’s Ramp Counting Procedure for Arbitrary Network Topologies: Some Examples of How to Count More with Less

Traffic counts are routinely gathered by transportation engineers and planners as they play essential roles in numerous transportation studies. Generally, counts are performed on the road segments that one is interested in, except for high volume freeways for which FHWA recommends using the ramp counting procedure. In this procedure, one essentially estimates what traffic volumes on freeway segments are based on traffic counts on their on- and off-ramps. The key notion is in FHWA’s ramp counting procedure is flow conservation. In this paper it is demonstrated, via examples, that the ramp counting procedure can be generalized for traffic networks of arbitrary topology. That is, instead of directly counting traffic volumes on all road segments in a transportation network, it is possible to only count a subset of them. The remaining traffic volumes can then be determined from the counted volumes with the aid of flow conservation. Practically speaking, this procedure has the potential to significantly reduce the amount of resources needed to perform traffic counts.