Nano-Interchange vs. the All-Directional Four-Level: A Comparison of Geometrics, Construction Costs, and Right of Way Requirements

Abstract

This thesis introduces the nano-interchange, an innovative concept in freeway-to-freeway interchange design, originating with Dr. Joseph Hummer, P.E., of North Carolina State University. Created with the intentions of minimizing the amount of right of way (or the "footprint") needed for an urban interchange, the nano-interchange may be an alternative design for densely populated and developed urban areas. The main objectives of this thesis were to establish design criteria and typical sections, develop the horizontal and vertical alignments, and estimate right of way requirements and construction costs for the nano-interchanges and comparison interchanges. While reviewing the feasibility of the nano-interchange concept, two design variations emerged, named the "reverse nano-interchange" and the "parallel nano-interchange" for their distinct geometric features. This document presents each of these interchange concepts at three different ramp design speeds (35, 45, and 55 miles per hour), for a total of six nano-interchange designs. As a comparison, we evaluated all six nano-interchanges against the all-directional four-level interchange (at the same three ramp design speeds).

Overall, the reverse nano-interchange with a ramp design speed of 35 miles per hour would need the least amount of right of way but is the most expensive interchange. The all-directional four-level interchanges would require the most right of way but cost less than the nano-interchanges of the same design speeds. The right of way requirements for the reverse nano-interchange, parallel nano-interchange, and all-directional four-level interchange range from approximately 39 to 68 acres, 49 to 70 acres, and 54 and 101 acres, respectively. Costs for the reverse nano-interchange, parallel nano-interchange, and all-directional four-level interchange range from $266M to $289M, $110M to $179M, and $83M to $150M, respectively. Construction cost estimates and right of way requirements do not increase linearly as the ramp design speeds increase in increments of ten miles per hour. Finally, this study concludes by recommending several geometric modifications to the designs, considerations of the advantages and disadvantages of the nano-interchange designs, and other research topics for further detailed study.