Browsing by Author "Dr. Billy M. Williams, Committee Member"

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Destination Choice Modeling of Trip Distribution for the Raleigh-Durham International Airport
(2007-07-24) Runey, Elizabeth Michelle; Dr. John R. Stone, Committee Chair; Dr. Nagui M. Rouphail, Committee Member; Dr. Billy M. Williams, Committee Member
This research develops a sub-model of the Raleigh-Durham International Airport (RDU) for the Triangle Region Travel Demand Model (TRM). The focus of the sub-model is on trip distribution using multinomial logit (MNL) models to explain the relationship between the airport trip makers (air passenger and employees) and destinations of the study area. The MNL models reflect the unique travel patterns of airport trips more than the gravity model by incorporating destination characteristics (number of households, employment type, and travel time) as well as trip maker characteristics (household income and household size). These characteristics are important to airport trip maker's choice of destination besides travel time and travel distance, especially when there are no major competing airports in the area. RDU airport surveys, RDU airport activity data, and TRM zonal data were used to develop MNL models for the HB, NHB, and J-to-W trip purposes. The airport surveys were the main data sources used in this research and the most challenging to format for trip distribution. Since the surveys were conduced for rail analysis and not for trip distribution, they did not capture enough complete observations trip distribution at the zonal level. Thus, the TAZ destinations were grouped by socio-economic (SE) group segment, and the MNL models were estimated using the Biogeme software. The resulting MNL model probabilities of airport trip makers choosing the SE group segment destinations were applied to the 2002XP TRM zones using relative attraction factors, and the trip interchanges between the RDU airport zone and all other zones in the study area were estimated. Finally, the RDU airport sub-model trip interchanges were input into the 2002XP TRM and traffic assignment of the RDU airport sub-model was estimated using the TransCAD software. The RDU airport trip interchanges of the sub-model compared to the TRM trip estimates show that the RDU sub-model estimates approximately 2,000 more trips per weekday than the 2002XP TRM. This is reasonable since the sub-model considers both air passenger and airport employee trips, where as the 2002XP TRM considers only employee trips. Additionally, the distribution of trips show that the RDU airport sub-model estimates more trips at destinations farther away from the RDU airport and more dispersed throughout the study area than the 2002XP TRM. This is logical since the RDU airport trip makers? travel farther to get to the airport than other types of trips such as grocery store trips and since most zones do not have a large number of weekday airport trips. The traffic assignment results of the two methods shows that the RDU airport sub-model traffic volumes are lower compared to the 2002XP TRM estimates and to the year 2002 AADT counts both in the vicinity of the RDU airport and the entire TRM study area. However, calibration of traffic assignment is not in the scope of this study, and additional data sources of the time of day and directional split factors for the RDU airport trips can improve traffic assignment. The benefits of this research provide a framework and methodology to develop and apply a sub-model for unique land uses such as an airport. The destination choice MNL model framework facilitates the modeling of airport trips in travel demand models, and it allows planners to focus limited resources of observed data in order to more precisely distribute airport trips. The RDU airport sub-model provides accurate estimates of RDU airport trips and it has potential to provide enhanced traffic assignment and air quality conditions in the Triangle Region. The foregoing results of this research have implications for transportation planning, airport modeling, air quality analysis and land use planning.
Determining Visibility Distance of Signs Installed on the Roadside Using Videologs
(2003-05-16) Baek, Changseok; Dr. Billy M. Williams, Committee Member; Dr. Leonard A. Stefanski, Committee Member; Dr. John R. Stone, Committee Member; Dr. Joseph E. Hummer, Committee Chair
The purpose of traffic signs is to provide information for the orderly movement that guides all road users as to direction, regulations and warnings. A driver may be able to view sign sheetings from a long distance with no sight obstruction. However, there are many cases in which the driver's line of sight is blocked by obstructions, such as trees, hills, curves, and other signs. These obstructions may reduce the effectiveness of the sheetings and therefore the frequency of safe response by drivers. The objectives of this project are to determine the distribution of the visibility distance for obstructed and unobstructed signs and to identify reasons for being obscure using videologs. The videologs contain images that can be used for this visibility distance study with the benefits of less cost, less potential danger, and less time than data obtained from a manual field survey. Most signs were obstructed. A little more than half of the obstructions were curves and hills, and trees were the most prevalent obstruction in the urban area that was biggest problem among the road types. About 25.4% of obstructed signs had less than 400 feet of visibility distance. In order to avoid the possible reduction of the effectiveness of traffic signs, sign placement should be considered during geometric highway design, and the impact of trees that may be growing should be taken into consideration.
Impact of Lane Drops on Intersection Capacity
(2005-12-30) Lee, Jae-Joon; Dr. Billy M. Williams, Committee Member; Dr. Pamela J. Arroway, Committee Member; Dr. Joseph E. Hummer, Committee Member; Dr. Nagui M. Rouphail, Committee Chair
Lane drops downstream of signalized intersections are found on many urban and suburban streets and highways. The short lane is typically under-utilized at the intersection since drivers avoid using the short lane due to the potential for stressful merges downstream of the signal. This unconventional geometric configuration downstream of the lane drop intersection affects intersection capacity and operations. The current Highway Capacity Manual (HCM) does not take into account downstream lane drop conditions, thereby resulting in significant discrepancy between the HCM defaults and field observed lane utilization factors (LUF). The primary objectives of this research were to identify whether and by how much lane drops affect performance of actuated signalized intersections under various traffic demand levels and lane drop geometries. The research developed LUF prediction models by intersection type from data on traffic, signal and intersection geometry collected in the field. The developed models imply that the downstream lane length and traffic intensity are positively correlated with the LUF and that other geometric variables at the approach may also influence lane utilization. Also, a traffic simulation model was used to quantify the impact of lane drops on intersection operations with various traffic volumes and geometric conditions. Through the simulation, it was found that additional green time, which should reduce delay, was created because of the overloaded full lane at the approach, however; a higher probability of green time termination with maximum green time dominates the benefit of extra green and the approach gains significant extra delays. Based on the data obtained from the simulation, this research quantified the amount of additional delay for the subject movement and established delay adjustment factors due to account for lane drop effects. Findings from this research are expected to contribute to the assessment of lane drop intersection performance.
Nano-Interchange vs. the All-Directional Four-Level: A Comparison of Geometrics, Construction Costs, and Right of Way Requirements
(2007-07-26) Harris, Meredith Louise; Dr. Joseph E. Hummer, Committee Chair; Dr. John R. Stone, Committee Member; Dr. Billy M. Williams, Committee Member
This thesis introduces the nano-interchange, an innovative concept in freeway-to-freeway interchange design, originating with Dr. Joseph Hummer, P.E., of North Carolina State University. Created with the intentions of minimizing the amount of right of way (or the "footprint") needed for an urban interchange, the nano-interchange may be an alternative design for densely populated and developed urban areas. The main objectives of this thesis were to establish design criteria and typical sections, develop the horizontal and vertical alignments, and estimate right of way requirements and construction costs for the nano-interchanges and comparison interchanges. While reviewing the feasibility of the nano-interchange concept, two design variations emerged, named the "reverse nano-interchange" and the "parallel nano-interchange" for their distinct geometric features. This document presents each of these interchange concepts at three different ramp design speeds (35, 45, and 55 miles per hour), for a total of six nano-interchange designs. As a comparison, we evaluated all six nano-interchanges against the all-directional four-level interchange (at the same three ramp design speeds). Overall, the reverse nano-interchange with a ramp design speed of 35 miles per hour would need the least amount of right of way but is the most expensive interchange. The all-directional four-level interchanges would require the most right of way but cost less than the nano-interchanges of the same design speeds. The right of way requirements for the reverse nano-interchange, parallel nano-interchange, and all-directional four-level interchange range from approximately 39 to 68 acres, 49 to 70 acres, and 54 and 101 acres, respectively. Costs for the reverse nano-interchange, parallel nano-interchange, and all-directional four-level interchange range from $266M to $289M, $110M to $179M, and $83M to $150M, respectively. Construction cost estimates and right of way requirements do not increase linearly as the ramp design speeds increase in increments of ten miles per hour. Finally, this study concludes by recommending several geometric modifications to the designs, considerations of the advantages and disadvantages of the nano-interchange designs, and other research topics for further detailed study.
Paratransit Customer Satisfaction With Real-Time Information: The Winston-Salem Trans-AID Case
(2003-10-29) Woodlief, John Ashley; Dr. Billy M. Williams, Committee Member; Dr. Joseph E. Hummer, Committee Member; Dr. John R. Stone, Committee Chair
Improving transit service to attract new riders is a primary goal for transit agencies. And tracking the effects of new services on customer satisfaction helps transit managers determine if they are making cost-effective decisions. This research examines the effects of improved telephone communication on customer satisfaction with transit service. Customer satisfaction data were collected before and after Winston-Salem Transit Authority installed an interactive voice response automated telephone system. Using a touch-tone telephone, passengers call WSTA to check on their paratransit trip status, cancel trip reservations, ask questions regarding transit service and policies, and conduct other trip-related functions. The research methodology uses three complementary methods to collect and process customer satisfaction data before and after the telephone system is installed: stated preference surveys, revealed preference data, and derived importance. Survey results indicate that customers adapted to using the automatic telephone system as a useful and reliable alternative to speaking with a WSTA operator. Surveys show a general increase in customer satisfaction with transit information and services, and analysis reveals a significant improvement in customer satisfaction and reduced frequency of waiting on hold or having to call back after receiving a busy signal. Derived importance analysis indicates rising customer expectations for transit service, especially the ease of calling WSTA and the time to confirm, cancel or book a trip. Revealed preference data confirm the results of the user surveys and demonstrate a significant shift of passengers from speaking to operators directly to using the automated touch-tone telephone system. Overall, the automated telephone system appears to be a valuable asset to Winston-Salem Transit.