Document Type

Thesis

Date of Award

5-2023

School/College

College of Science, Engineering, and Technology (COSET)

Degree Name

MS in Transportation Planning & Management

Committee Chairperson

Yi Qi

Committee Member 1

Fengxiang Qiao

Committee Member 2

Mehdi Azimi

Committee Member 3

Shahryar Darayan

Keywords

• Calibration • Delay • Diamond Interchange • Traffic Model • Traffic Signal • Traffic Volume

Abstract

Interchanges are critical elements of modern transportation networks. A new design called the Flipped Left-Turn Diamond Interchange (FLDI) has been proposed to enhance efficiency and increase the capacity of traditional diamond interchanges. The FLDI design features left-turn lanes in opposing directions, eliminating conflicts between opposing left-turn movements. One of the key benefits of FLDI is its ability to be easily implemented within the existing right of way, without the need for major construction or the elimination of direct connectivity between frontage roads or access to corner properties, unlike other innovative designs such as the Diverging Diamond Interchange (DDI) and Continuous Flow Intersections (CFI). The primary objective of this study is to investigate whether implementing the FLDI design can reduce vehicle delay, queue length, and the number of stops compared to a conventional diamond interchange. Additionally, the study aims to determine the applicable conditions for implementing the FLDI design and develop signal timing strategies to optimize its performance. To achieve this objective, various data types, including turning movement counts, travel time, and signal timing data, were collected at a diamond interchange in Fort Worth, Texas. Microscopic traffic models were then developed for the existing condition (conventional diamond interchange) and the FLDI design in PTV VISSIM. The base model was calibrated based on travel time and traffic count data to ensure that the developed model accurately represents the existing condition. In addition, a new signal timing plan was developed for FLDI to improve operational performance at the interchange. This phasing plan provides the traffic progression time between the two intersections at the diamond interchange and prevents the green starvation problem at the downstream intersection. The study found that FLDI is more robust than the conventional diamond interchange when subjected to heavy traffic conditions. The traffic simulation results showed that the implementation of FLDI may reduce vehicle delay, queue length, and the number of stops at the entire interchange by 30% to 40%, 30% to 50%, and 30%, respectively. The main reason for this improvement is that FLDI can allow more traffic flows to move simultaneously in one phase. Furthermore, it was found that the performance of FLDI was almost the same as the conventional diamond interchange when the interchange experiences low and medium traffic. To address traffic safety concerns, it is recommended that FLDI have a dedicated U-turn lane between the frontage roads. This study proposes that FLDI can be a viable design option for diamond interchanges with heavy traffic volume conditions due to its ability to reduce travel delays, stops, and queue lengths. Its feasibility should be evaluated carefully based on local traffic conditions and engineering judgment before implementation. This study can assist traffic engineers and transportation planners in the operational analysis of diamond interchanges.

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