A critical assessment of methodologies for operations and safety evaluations of freeway turbulence

Turbulence in traffic is a commonly known phenomenon, but the exact characteristics of this phenomenon are not yet clear. It reflects individual changes in speed, headways, and lanes in the traffic stream. The currently used freeway design guidelines prescribe different measures for handling turbulence, such as sufficient ramp spacing, and spacing between road discontinuities. In situations where the available space between discontinuities is scarce, it might be necessary to make a trade-off between costs and safety/operation. For a valid trade off more insight is needed on the safety and operations effects when one deviates from the guidelines. A lot of research was done on the different causes of turbulence and their effect on safety and operation. This paper proposes a theoretical framework for turbulence phenomenon that facilitates the comparison of the available methodologies that can be used to evaluate a freeway design on the matter of turbulence and its impact on traffic operations and safety. The main finding of this review is that the currently available methodologies lack the ability to evaluate the impact of freeway turbulence on operations and safety simultaneously. Different recommendations to overcome limitations of current methodologies and further research possibilities to improve these methodologies are given