The increase in surface transportat

The increase in surface transportation and number of vehicle miles traveled has led to new challenges for the transportation planners and engineers of ascertaining safe and uninterrupted flow of people and goods. These challenges can be met by employing some innovative and cost-effective methodologies for solving transportation problems. One of these methodologies is the Diverging Diamond Interchange (DDI).
The main goal of the DDI design is to better accommodate left-turn movements and hence eliminate a phase in the signal cycle. There is no change in the freeway portion but the off-ramp and on-ramp movements change for left-turns. In a DDI, through and left-turn traffic on the crossroad maneuver differently from a conventional diamond interchange as the traffic crosses to the opposite side in between the ramp terminals.
The DDI design was first suggested by Chlewicki (2) and a case study was performed using Synchro. Edara et al. (1) had earlier performed an analysis of the DDI using VISSIM for different volume scenarios and lane configurations. The results from both of these studies suggested that the DDI design outperforms the conventional interchange design for a balanced interchange traffic volume scenario. Federal Highway Administration (FHWA) has recently performed a driver’s evaluation of the DDI and reported that the design has safety benefits combined with the predicted operational benefits and reduced right-of-way requirement.
In this paper we further analyze the DDI design for unbalanced interchange traffic volume scenarios. Also, this research includes a cost-effectiveness analysis of the DDI as compared with a conventional interchange design. The aim of this research is to determine the additional benefits of using a DDI design in place of a conventional interchange design in terms of user and construction costs. The results are reported and some recommendations are made on the circumstances best suitable for selecting DDI as an alternative.
The first section of the paper describes the designs of the DDI and the conventional diamond interchange under analysis. The second section describes the methodology used, model development, traffic scenarios analyzed and the type of data collected. The third section presents the results and findings of the research and the last section gives conclusions and recommendations and the need for further research.