Investigation of Design Speed Characteristics on Freeway Ramps using SHRP2 Naturalistic Driving Data

Freeway ramp design guidance has existed in the United States for many decades, coinciding with the advent of the nation’s freeway network and the Interstate Highway system. Some principles associated with ramp design are largely unchanged since their inception, and a review of those principles in the context of today’s drivers and vehicles is beneficial for identifying potential updates to existing guidance. The process of collecting the necessary data may consist of a variety of methods, each with limitations on the number of ramps, vehicles, and trips that can be studied. A current research project is exploring the feasibility of using data from the Strategic Highway Research Program 2 (SHRP2) Naturalistic Driving Study (NDS) to identify relationships between ramp design speed characteristics and drivers’ choices of operating speeds on those ramps. The NDS data provides a dataset that is unprecedented in its size and detail, but its suitability for this type of analysis is largely unknown. This paper summarizes the activities and findings of the current research project, including basic models for estimating vehicle speeds on freeway ramps based on the NDS data; these models may be used in conjunction with other ongoing related research efforts to suggest material for potential updates to existing ramp design guidance.