Browsing by Subject "Diamond Interchange"
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Item Development and evaluation of operational strategies for providing an integrated diamond interchange ramp-metering control system(Texas A&M University, 2004-09-30) Tian, ZongzhongDiamond interchanges and their associated ramps are where the surface street arterial system and the freeway system interface. Historically, these two elements of the system have been operated with little or no coordination between the two. Therefore, there is a lack of both analysis tools and operational strategies for considering them as an integrated system. One drawback of operating the ramp-metering system and the diamond interchange system in isolation is that traffic from the ramp, particularly if it is metered, can spill back into the diamond interchange, causing both congestion and safety concerns at the diamond interchange. While flushing the ramp queues by temporarily suspending ramp metering has been the primary strategy for preventing queue spillback, it can result in freeway system breakdown, which would affect the entire system's efficiency. The aim of this research was to develop operational strategies for managing an integrated diamond interchange ramp-metering system (IDIRMS). Enhanced modeling methodologies were developed for an IDIRMS. A computer model named DRIVE (Diamond Interchange and Ramp Metering Integration Via Evaluation) was developed, which was characterized as a mesoscopic simulation and analysis model. DRIVE incorporated the enhanced modeling methodologies developed in this study and could be used to perform system analysis for an IDIRMS given a set of system input parameters and variables. DRIVE was validated against a VISSIM microscopic simulation model, and general agreement was found between the two models. System operational characteristics were investigated using DRIVE to gain a better understanding of the system features. Integrated control strategies (ICS) were developed based on the two commonly used diamond interchange phasing schemes, basic three-phase and TTI four-phase. The ICS were evaluated using VISSIM microscopic simulation under three general traffic demand scenarios: low, medium, and high, as characterized by the volume-to-capacity ratios at the metered ramps. The results of the evaluation indicate that the integrated operations through an adaptive signal control system were most effective under the medium traffic demand scenario by preventing or delaying the onset of ramp-metering queue flush, thereby minimizing freeway breakdown and system delays.Item Investigation of the Implementation of Ramp Reversal at a Diamond Interchange(2013-06-25) Wang, BoDiamond interchange design has been commonly utilized in United States to facilitate traffic exchange between freeway and frontage roads. Another less common interchange design is X-ramp interchange, which is the reversed version of diamond. The major benefit of X-ramp interchange is that it can keep travelers on the freeway until the downstream exit ramp to avoid going through the intersection. It also has drawbacks such as travelers with cross street destinations will experience more delay. This study focuses on when the ramp reversal is desirable. To compare the diamond and X-ramp design, an experimental design is conducted using Latin Hypercube Design method. Four varying factors include interchange design type, traffic volume on the frontage road, through movement percentage and saturation rate of the intersection. 40 scenarios are generated for simulation study using Synchro and VISSIM. Based on the simulation study, optimal signal timing strategies are recommended for each type of interchange design under various traffic conditions. Also, ramp reversal is found closely related to the following factors such as interchange frequency, upstream interchange design, traffic volume on frontage road, through movement percentage and intersection saturation rate. Conclusions are made on when X-ramp is better than diamond interchange design. At last, future research directions are recommended.