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A new decision making approach for indirect left turn treatments by utilizing decision assistance curves
This study developed decision assistance curves (DAC) for unconventional intersections, including median U-turns (MUT), continuous flow intersections (CFI), and jughandle intersections, based on their operational performance relative to a conventional intersection. An economic analysis was performed to compute the net present value (NPV) of benefits and the benefit to cost ratio (B/C) with the development of a spreadsheet tool. The DAC classified the region of optimal performance of isolated unconventional intersections. For 5% left turn traffic conditions, MUT was warranted for all volume criteria. For 10% and 15% left turn traffic conditions, jughandle was warranted for the major street approach traffic volumes greater than or equal to 2200 vph, and greater than 1800 vph, respectively. However, the warranty decreased with the increase of minor streets for all of the conditions except at balanced and nearly balanced conditions under 10% left turn traffic. For 10% and 15% left turn traffic conditions with an unbalanced flow, CFI was warranted for major street approach traffic volumes greater than or equal to 2200 vph, and greater than 1800 vph, respectively. The warranty expanded with the increase of minor street approach traffic volumes. The standard signalized intersection with left turn permitted was warranted for minor street approach traffic volumes less than 200 vph and the major street approach traffic volumes of 700 vph to 1350 vph. The high presence of trucks favored the use of CFI. Additionally, a case study performed on a 24-hour rural pattern volume indicated the highest NPV of benefits and the highest B/C related to new MUT construction. Though the MUT-retrofit had the highest NPV, since the construction cost of MUT-retrofit was high, a jughandle-retrofit was found to have the highest B/C. In this manner, the developed method provided an integrated decision support system utilizing both operational performance and economic aspects as an improved method over the current practice. Some possible extensions of study were also recommended as further studies.
Gyawali, Sunil, "A new decision making approach for indirect left turn treatments by utilizing decision assistance curves" (2014). ETD collection for University of Nebraska - Lincoln. AAI3646034.