Award Date


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Civil and Environmental Engineering

Number of Pages



The primary objective of the research presented in the dissertation, Analysis of Saturation Flows at Single, Dual and Triple Left-Turn Lanes, is to gain a better understanding of the operational characteristics of single and multiple left-turn lanes as compared to adjacent through-lanes on the same intersection approach. The findings of this study are based on average saturation flow headways as observed between the 4th and 8th vehicles within a saturation queue discharge. These observations were made for left turn movements at signalized intersections with protected left-turn phases. The findings of this study are based on field measurements taken at 62 individual intersection approaches located on major arterial streets throughout the Las Vegas Metropolitan Area of Nevada outside the Central Business District of the urbanized community. The field observations are from 23 single, 36 dual and 3 triple left-turn lane intersection approaches comprised of 35 individual intersection sites. The collected saturation flow data contained in this study for analysis represents a total of 3,662 time observations of four vehicles each or a total of 14,648 individual passenger vehicles. The intersection sites were selected to be comparable among each other for geometric and operational conditions as well as driver behavior; The findings of this study support the 1994 Highway Capacity Manual suggested ideal through-lane saturation flow rate of 1900 (pcphgpl). However, the field observations suggest that the left-turn factor for single left-turn lanes with protected left-turn signal phasing should be 1.0 and dual left-turn lanes should be a minimum of 0.98 per Lane The results represent a significant increase over the suggested left-turn factor of 0.95 as recommended within the 1994 Highway Capacity Manual. The triple left-turn lane observations were found to continue to support an average left-turn factor of 0.95. These observations should be of particular interest to transportation engineers and planners who are responsible for the evaluation and development of cost-effective alternatives to improve at-grade signalized intersection capacities as the results indicate higher than expected left-turn capacities relative to the adjacent through lanes.


Analysis; Dual; Flows; Lanes; Left; Patternsflows; Saturation; Single; Traffic; Traffic Patterns; Triple; Turn; Traffic Patterns

Controlled Subject

Civil engineering

File Format


File Size

5468.16 KB

Degree Grantor

University of Nevada, Las Vegas




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