Operational analysis of the flipped left diamond interchange design for the freeways with frontage roads

Abstract

Recently, an alternative design called the flipped left-turn diamond interchange (FLDI) has been recommended to enhance efficiency and increase the capacity of diamond interchanges in Texas, where most of the freeways have frontage roads. This design flips left-turn lanes in opposing directions, eliminating conflicts between opposing left-turn movements. The design can be easily implemented within the existing right-of-way (ROW) without the need for major construction. FLDI also has many advantages over other existing designs at locations where frontage roads were presented. However, a very limited number of studies have been conducted to investigate its operational impacts and the strategies for implementing this design. To fill this gap, the primary objective of this study is to investigate the operational impacts of FLDI design. It also aims to investigate the signal timing, traffic signs, and geometric design issues in implementing the FLDI design. To achieve these objectives, a diamond interchange in Fort Worth, Texas, was selected as a study site. Microscopic traffic models were then developed for this interchange under the existing condition of conventional diamond interchange (CDI) and the condition with the implementation of FLDI design. The traffic simulation results showed that FLDI can significantly reduce vehicle delay, queue length, and the number of stops at the diamond interchange under heavy traffic conditions. In addition, a new signal timing plan was developed for FLDI to improve its operational performance. Furthermore, to ensure the safe operation of this new design, some recommendations on roadway design, traffic signs, and pavement markings were also proposed. The results of this study can facilitate the implementation of FLDI design.