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. Turbulence reflects individual changes in speed, headways, and lanes in the traffic stream. The current freeway design guidelines prescribe measures for handling turbulence, such as sufficient ramp spacing and spacing between road discontinuities. In situations where there is little available space between discontinuities, it might be necessary to make a trade-off between costs and safety and operations. For a valid trade-off, more insight is needed on the safety and operations effects of deviations from the guidelines. Much research has been done on the causes of turbulence and their effects on safety and operations. This paper proposes a theoretical framework for the 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. The paper makes recommendations to overcome the limitations of current methodologies and for further research possibilities to improve these methodologies.