Effects of Far-Side and Side Street Bus Stops on the Saturation Flow Rate of Signalized Intersections

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Title: Effects of Far-Side and Side Street Bus Stops on the Saturation Flow Rate of Signalized Intersections
Author: Fetter, William Woodrow
Advisors: Dr. Nagui M. Rouphail, Committee Member
Dr. John R. Stone, Committee Member
Dr. Joseph E. Hummer, Committee Chair
Abstract: As the use of public transit buses increases, it is important to understand how bus stops affect the surrounding traffic stream, especially with regards to intersection saturation flow rate. The HCM 2000 and other sources have addressed the effect of near-side bus stops, but no one has successfully analyzed bus stops on the far-side or side-streets of an intersection. The purpose of this study was to determine the effects that both far-side and side-street bus stops have on the saturation flow rate at a signalized intersection. To determine these effects, a set of analytical equations was derived for each bus stop type. The methodology for these equations required calculating the number vehicles processed through the intersection during each of three defined time periods within the green indication of a cycle. The time periods were divided according to how the buses blocked the traffic: full blockage (period 1), partial blockage (period 2), and no blockage (period 3). The average number of vehicles processed during a cycle was determined by multiplying each of the vehicles processed in a time period by the probability of buses stopping in that time period and then summing them together. The average number of vehicles processed was then divided by the ideal number of vehicles processed (obtained from simulation) to obtain an adjustment factor. Applying this factor to the saturation flow rate calculated the effects due to the bus stop. To analyze the ability of the equations to predict saturation flow rates, they were tested using a variety of variable inputs and compared with CORSIM simulation runs using the same inputs. Sensitivity tests were also performed to determine how the equations reacted under a variety of variable extremes. The results from these analyses were not exactly ideal and, as a result, the equations could only be partially validated. Overall, while it appears that the method for determining saturation flow rate according to the HCM is inaccurate, an adequate replacement method has not yet been developed. Although the methodology presented in this study is based upon more sound logic and appears to suggest a better method than the one dictated in the HCM, the equations still need to be improved and refined to create an effective replacement.
Date: 2007-04-24
Degree: MS
Discipline: Civil Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/668

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