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NCHRP Project 03-88: Guidelines for Ramp and Interchange Spacing

KAI completed research on developing ramp and interchange spacing guidelines, based on quantitative information obtained from actual field observation, theoretical considerations, simulations, and a combination of the three approaches. KAI completed this work to update and expand upon 1970’s-based information presented in the AASHTO Green Book as Exhibit 10-68.

KAI's research highlighted the safety and operational trade-offs, as well as others, associated with varying ramp and interchange spacing dimensions for the full range of service interchange. The research included developing a historical perspective on the origins of “one mile” interchange spacing and other ramp spacing considerations. The research team completed a comprehensive traffic operations modeling exercise and safety review of several hundred freeway miles to assess the operations and safety relationships of interchange and ramp spacing. KAI generated numerous case studies to support and reinforce the concepts of the guidance document. The Guidelines reflect a performance based approach to freeway ramp spacing determinations.