Browsing by Author "Billy Williams, Committee Member"

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Determining Path Flows in Networks: Quantifying the Tradeoff between Observability and Inference
(2008-04-24) Demers, Alixandra; Billy Williams, Committee Member; William A. Wallace, Committee Member; Nagui Rouphail, Committee Member; Yahya Fathi, Committee Member; George F. List, Committee Chair
Evaluating the Use of Red Light Running Photographic Enforcement Using Collisions and Red Light Running Violations
(2005-02-15) Cunningham, Christopher Michael; Joseph E. Hummer, Committee Chair; Billy Williams, Committee Member; Nagui Rouphail, Committee Member
The issue of red light running (RLR) has long been a problem throughout the United States. There is considerable debate within the general public and public agencies regarding the use of photographic enforcement to deter red light violations. Many studies have been conducted on the effectiveness of red light cameras (RLCs) at reducing collisions. However, the question still remains as to whether RLCs actually change driver behavior. Many municipalities across the State of North Carolina have relied on studies conducted in other states or countries to validate the use of cameras within their jurisdiction. Many of these studies are weak and could be more rigorous. The need for more thorough study motivated this research effort to help define the effectiveness of RLCs within the City of Raleigh, North Carolina. Four specific tasks were identified to help in this research effort. First, a literature review was conducted to determine the reported effects of other research efforts throughout the United States and other countries. Various types of studies have been conducted around the world. Of particular interest were studies that were rigorous in nature, such as those using comparison sites. Many studies completed in previous research indicate that RLC enforcement reduces the frequency of collisions at treated intersections. However, there are a limited number of rigorous studies (especially those in the United States, particularly in North Carolina). Analyses that used comparison sites usually did not perform tests to see if comparison sites acted in a similar manner to treatment sites. Six focus groups were convened in an effort to gather information on attitudes, opinions, and beliefs associated with photographic enforcement to better enhance traffic law enforcement. Two community and four professional focus groups were assembled. Overall, the perception of photographic enforcement was positive. Suggested improvements included enhancing the appeal process, using profit for local government support such as schools or more enforcement, and placing traffic signals in flashing red and yellow at low volume intersections during early morning hours of operation. The majority of participants agreed that the presence of RLCs would make them more aware of individual driver behavior; however, most of the groups agreed that the range of driver education varied widely and that educating the public should be a priority. In an effort to analyze the effect of RLCs on driver behavior, two types of analyses were completed. The first type of analysis was a before-after collision study. The following three types of improved before-after collision studies were used: accounting for causal factors, a comparison group analysis, and an improved comparison group analysis accounting for the halo-effect. Each of these studies analyzed four categories of collisions including the following: total, red light running related, angle, and rear end. Based on the comparison group study, collisions were effectively reduced by 17%, 22%, 42% and 25%, respectively. In addition to the analysis of collisions, red light running violations were analyzed to see if there was a change in driver behavior related to dangerous violation times (violations considered to possibly cause collisions) greater than two seconds. Using the Chi-Square Test of Independence, the frequency of unsafe red light running violations reduced significantly with a p-value less than 0.001. Based on these findings, RLCs appear to have a positive effect on driver behavior. Focus groups indicate that overall there is a positive perception of RLCs as a countermeasure to deter red light running. Based on the comparison group collision study, all collision group types decreased considerably. Lastly, red light running violations related to dangerous red light violation times dramatically decreased, providing further justification for the use of RLCs as a red light running countermeasure.
A Model and Optimal Schedule Design for a Fixed Bus Route.
(2007-04-06) Koshute, Phillip; Xiuli Chao, Committee Chair; Salah Elmaghraby, Committee Member; Billy Williams, Committee Member
Transit passengers' average total trip time can be minimized by employing the schedule that achieves the optimal balance between initial delay (tardiness) and layover time (earliness). To compare different proposed schedules, we carry out a deterministic simulation which uses link times taken from historical data in the order that they originally occurred. The simulation's arrival and departure times, in general, are not the same as those in the original data because a different schedule is in place. We measure total trip time by tracking deviations between the scheduled and simulation departure times and computing an appropriately weighted sum (reflecting the number of passengers affected by a given deviation). We consider the number of vehicles serving the route, the number of time-points N, and the scheduled cycle length to be fixed. Schedules are represented by 1-by-N solution vectors whose elements correspond to intervals between scheduled departure times of consecutive time-points. A Modified Steepest Descent (MSD) algorithm is used to search for the optimal solution. Throughout the project, North Carolina State University's Werewolf A bus route is used as a test case. Twenty-four days of historical data are utilized. Empirical results suggest that the space of feasible solutions may be convex. An optimal solution is identified and verified by a brute force search of all feasible solutions.
Modeling Impact of and Mitigation Measures for Recurring Freeway Bottlenecks
(2008-03-06) Clark, Zachary Thomas; Joe Hummer, Committee Member; Billy Williams, Committee Member; Nagui Rouphail, Committee Chair
Recurrent congestion is a continually growing problem on urban freeways. Facility expansions cannot keep pace with the growing vehicle demand. Low-cost mitigation measures are one way to alleviate the congestion at recurring bottleneck locations. Low-cost measures typically have a life of approximately 10 years and costs ranging from $8,000 to $2.45 million. While benefits have been realized in field applications, there hasn't been a lot of study regarding the performance of these measures in terms of added capacity. While modeling has long been a tool for planning and analyzing freeway networks, there has been little reported regarding its use for estimating the benefits of low-cost freeway improvements. In this study, the author tested proposed treatments at two sites using both a macroscopic and microscopic model. Because empirical performance information of these measures is not available, a quantitative analysis would not be reasonable since confidence in the values reported would be low. Current bottleneck identification methods typically either predict breakdown in real-time, or analyze detector data off-line. In order to identify bottlenecks from recorded aggregated data in an off-line model, criteria were generated to identify active bottlenecks and analyze the models' performance in an empirical and qualitative manner. Application of the criteria has been shown to provide reliable bottleneck identification to the calibrated pre-treatment case and expected results in the post-treatment cases.
Operational Effects of Signalized Superstreets in North Carolina.
(2010-05-12) Haley, Rebecca; Joseph Hummer, Committee Chair; Billy Williams, Committee Member; Nagui Rouphail, Committee Member
Safety Effects of Superstreets in North Carolina.
(2010-10-01) Ott, Sarah; Joseph Hummer, Committee Chair; Nagui Rouphail, Committee Member; Billy Williams, Committee Member
Validation of APA Design Criteria for Field Surface Mixtures.
(2010-10-18) Reddy, Kallem; Narendra Khosla, Committee Chair; Billy Williams, Committee Member; M. Rahman, Committee Member
Weigh in Motion Data Analysis
(2009-11-02) Ramachandran, Aditya Narayanan; John Stone, Committee Chair; William Rasdorf, Committee Member; Billy Williams, Committee Member
At hundreds of Weigh in Motion (WIM) stations, State Departments of Transportation collect traffic data every year to support pavement design, to enforce weight restrictions on highways and bridges, and to provide planning data for highway improvements. Reliable WIM data is particularly important to support the procedures in the FHWA Mechanistic Empirical Pavement Design Guide (MEPDG). The purpose of the research is to identify and resolve four related but relatively stand-alone problems associated with WIM data collected by NCDOT. Quality Control: After the NCDOT collects WIM data and converts it from proprietary vendor format to an ASCII text format, the quality of the data must be checked. During the quality control (QC) procedures, tests identify incomplete datasets, out of range values for individual vehicle classes, and other possible data problems. Vehicle class and weight checks generate 0.97% and 6.42% anomalies, respectively thus confirming that NCDOT equipment captured reliable WIM measurements. NC Urban and Rural Truck Traffic Profiles: Knowing the type of traffic by vehicle class by highway functional classification is critical to designing, maintaining and paying for North Carolina highway pavements. Thus, GVW plots by vehicle class and highway functional class are very important. The results indicate that in general, the class 5 and 9 GVW plots for all categories of WIM stations show expected trends. These results may be used by highway planners and pavement designers to quickly determine typical truck traffic profiles in the various NC regions and provide insight into NC truck transportation flows. NC vs. University Of Arkansas WIM QC Analysis: Most highway agencies have the data collection and design groups in different units. While a single software solution is not practical, it is recommended to perform two separate processes where the output of data QC meets the needs and standards of the design process. A comparative analysis between the QC methods followed by the University of Arkansas (UARK) and NCSU/NCDOT shows that while the UARK Pavement Designer software has better mapping functions and supports data analysis and design. However, from a WIM data analystÃ¢â‚¬â„¢s perspective it is a Ã¢â‚¬Å“black boxÃ¢â‚¬Â . In addition there is significant data reduction involved and the rigid nature of an automated QC process does not provide enough justification for the data to be used as input for the MEPDG. On the other hand, the NCSU/NCDOT approach is a two step procedure with a comprehensive QC procedure that provides the flexibility of manual overriding based on local knowledge of WIM stations and a separate unit managing the pavement design element. WIM Data Management and Analysis in SQL Server: While most research topics focus on collection and quality of data with little emphasis on the development of an integrated Database Management System (DBMS) to store and analyze traffic data. An innovative approach to perform quality control procedures and data analysis on two test WIM databases by using analysis cubes in SQL Server is the main objective of this chapter. It is a convenient method of disseminating data to users that do not have online access to the WIM database in SQL Server. The analysis cube files may also be used for data mining and exploration and could be used to observe trends in axle weights, axle spacings, vehicle class volumes etc. An additional objective is to discuss the advantages of transitioning from Access to a more comprehensive DBMS like SQL Server or Oracle to store and analyze WIM data for the NCDOT statewide WIM program.