abstract: ABSTRACT This study examines the methodology for converting protected, permissive, and protected/permissive left-turn operation to flashing yellow arrow left-turn operation. This study addresses construction-related considerations, including negative offsets, lateral traffic signal head position, left-turn accident rates, crash modification factors and crash reductions factors. A total of 85 intersections in Glendale, Arizona were chosen for this study. These intersections included 45 “arterial to arterial” intersections (a major road intersecting with a major road) and 40 “arterial to collector” intersections (a major road intersecting with a minor road). This thesis is a clinical study of the field conversion to flashing yellow arrow traffic signals and is not a study of the merits of flashing yellow arrow operation. This study included six categories: 1. High accident intersections (for inclusion in Highway Safety Improvement Program (HSIP) funding); 2. Signal head modifications only; 3. Signal head replacement with median modifications; 4. Signal head and mast arm replacement; 5. Signal head, signal pole and mast arm replacement; and 6. Intersections where flashing yellow arrow operation is not recommended. Compliance with the Manual on Uniform Traffic Control Devices (MUTCD) played a large part in determining conversion costs because the standard for lateral position of the left-turn traffic signal greatly influenced the construction effort. Additionally, the left-turning vehicle’s sight distance factored into cost considerations. It’s important for agencies to utilize this study to understand all of the financial commitments and construction requirements for conversion to flashing yellow arrow operation, and ultimately to appreciate that the process is not purely a matter of swapping traffic signal heads. / Dissertation/Thesis / Masters Thesis Civil Engineering 2016

In the United States, there are two schemes of operating traffic signal controls for permitted protected left turns (PPLT) namely the traditional five-section head system (known as Dog-House) and the flashing yellow arrow system (FYA). Past studies have agreed that these controls lead to decrease the average delay per left turn vehicle, decrease the protected green time, increase the left turn capacity, and enhance the intersection overall operation. The flashing yellow arrow (FYA) has been approved by the Federal Highway Administration as the national standard for the PPLT operations at signalized intersections. So, the Florida Department of Transportation also approved this new system and they are extensively replacing the traditional system with the new system on the area of Central Florida (Lin, et al, 2010). Both these systems have been used for a long time and there are some studies that evaluated these systems but there are limited number of projects that evaluated and/or compared between the two PPLT systems from the operational perspective. The main goal of this research is to study the characteristics of traffic operations and evaluate the effectiveness of the conversion from five-section head signal to the FYA treatments at 13 intersections located in Orlando, Florida. To reach this goal, detailed data collection efforts were conducted at 13 selected intersections in the central Florida area and appropriate statistical tests were conducted using the Minitab 17 Software. Statistical tests were attempted to fit different new regression models that correlate delay and left turn volumes as response variables against a set of independent variables that included permitted green time, opposing volume, percent of trucks, time gaps, speed, and land use type. In addition to fitting the data to regression models, these models were also analyzed for the purpose of detecting any significant differences between the five-section head treatment and FYA treatment. The statistical differences of converting the five-section head system to FYA system were discussed. The results in this thesis agreed with some of the previous studies and did not agree with others. In general, the flashing yellow arrow system was found to enhance the intersection operation, increase the number of left turn vehicles, and reduce the delay. Also, some suggestions and recommendations were made based on this study results.

Since their introduction to the 2009 Edition of the Manual on Uniform Traffic Control Devices, flashing yellow arrows (FYA) have had significant success in communicating the permissive turn message. While widely used for the permissive left turn maneuver, agencies recently have been utilizing flashing yellow arrows for the use with right turn applications as drivers interact with crossing pedestrians. As pedestrian conflicts are a concern during the permissive green phase, there is additional worry for the potential interaction between a pedestrian and vehicle turning right on red. This research explores the existing driver comprehension of permissive right turns during both green and red phases through static evaluation and microsimulation. Proposed traffic devices including the FYA and the Dynamic No Turn on Red sign were evaluated in relation to the existing signal and sign conditions implemented in the field. In comparing the proposed FYA to the existing circular green signal, the survey evaluation determined a statistically significant increase in drivers’ yielding responses when interacting with the FYA as opposed to the circular green. Through application of the VISSIM program, it was determined that right turning speeds with the FYA present were significantly lower than when interacting with solely the circular green. Both the static evaluation and microsimulation determined a strong similarity between the existing circular red and R10-11 sign and the proposed dynamic no turn on red sign which verifies the strong understanding drivers have of the message and the sign itself.

According to NCHRP Report 493, there are five major left turn signal indications for permitted operations in the United States. They are: Circular Green (CG), Flashing Circular Red (FCR), Flashing Red Arrow (FRA), Flashing Circular Yellow (FCY) and Flashing Yellow Arrow (FYA). The main goal of this thesis is to study the driver behavior and analyze safety of drivers for different left turn indications using a real-time driving simulator. Different signal indications alter driver behavior which influences velocity and acceleration profiles. These profiles influence vehicular emissions and hence need to be studied as well. For this purpose, different scenarios are implemented in the driving simulator. Data is analyzed using Microsoft Excel, JMP Statistical tool and MATLAB. Safety of drivers is analyzed with respect to the parameter "Time to Collision (TTC)" which is directly obtained from simulator data. Vehicular emissions and fuel consumption are calculated using VT-Micro microscopic emissions model. Graphs are plotted for TTC and total emissions. Results indicate that for a day-time scenario, FCY and FYA are the most suitable left-turning indications whereas FCR and FRA are most suitable for a night-time scenario. / Master of Science / There are five major left-turn indications for permitted operation in the United States. They are: Circular Green (CG), Flashing Circular Red (FCR), Flashing Red Arrow (FRA), Flashing Circular Yellow (FCY) and Flashing Yellow Arrow (FYA). Different states use different left-turn indications throughout the country. The level of driver comprehension for a particular signal indication will have an effect on the driving behavior and this in turn will affect fuel consumption and total emissions. The main goal of this thesis is to study driver behavior for different left-turning operations and to provide guidelines for the selection of signal indications. For this purpose, a real time driving simulator is used and different scenarios are implemented for left-turning operations. Data has been collected from the simulator to analyze driver safety in each scenario. Velocity and acceleration data from the simulator is used to calculate vehicular emissions to analyze environmental impact. The signal indication that best suits a given situation should provide maximum driver safety and minimum environmental impact. Graphs are plotted and results indicate that, during day time FCY and FYA are the most suitable indications whereas FCR and FRA are best suited for a night time scenario.