Browsing by Author "Dr. Joseph E. Hummer, Committee Chair"

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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.
Effects of Far-Side and Side Street Bus Stops on the Saturation Flow Rate of Signalized Intersections
(2007-04-24) Fetter, William Woodrow; Dr. Nagui M. Rouphail, Committee Member; Dr. John R. Stone, Committee Member; Dr. Joseph E. Hummer, Committee Chair
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.
The Human Factors Effects of Nine-panel Logo Signs
(2007-05-10) Maripalli, Uday Krishna; Dr. Joseph E. Hummer, Committee Chair; Dr. John R. Stone, Committee Member; Dr. Kimberly S. Weems, Committee Member
At many interchanges on North Carolina freeways, the number of businesses providing motorist services has grown. When the number of qualifying businesses providing a certain service at an interchange exceeds the number of logo panels allowed per sign—currently six—the NCDOT faces a dilemma. One option for the NCDOT is to increase the number of logos allowed per sign. The main concern is for motorist safety, in that drivers taking longer to read and comprehend signs may be distracted from more important parts of the driving task. The objective of this project was to determine whether nine-panel logo signs cause negative impacts on drivers from a human factors point of view. In particular, this project attempted to determine: 1. How do drivers use logo signs? 2. Are drivers using logo signs with more than six logos distracted away from driving tasks more than drivers using logo signs with six panels? Objective one was achieved by administering a driver survey. A 10-question form was developed, and the survey was administered at two rest areas off of interstates that already have some pilot nine-panel logo signs. The survey data provided insight into how motorists use panel logo signs. It was found that more drivers scan logo signs for a particular brand than read all of the logos. It was also found that most drivers use logo signs at some point, and that the most-frequently used logo sign is for gasoline, followed by the sign for food. However, drivers do not scan for particular brands of gasoline as often as for food or lodging. The second objective was achieved by conducting a slide-based experiment and by developing driver information load profiles. Thirty seven volunteer subjects participated in the experiment, in which the subjects were first given the name of a brand to scan for and were asked to indicate with a "yes", "no", or "not sure" response whether the specific business was represented on the sign. Six-panel and mixed-use signs performed better than nine-panel signs. However, the margin of difference in many cases was not significant. It was concluded that nine-panel logo signs performed well from a human factors point of view. Their correct response percentages were usually competitive with, and sometimes surpassed, the mixed-use signs, and were not far behind those of the six-panel signs. Driver information load profiles were developed using "Driver Information Load Software" developed by NCHRP to compare the load given to a driver by six panel logo signs to nine panel logo signs. A three lane highway of 11000 ft with one exit where the driver is assumed to make a maneuver was analyzed for six-panel and nine-panel logo signs. At a single point on the roadway, a nine-panel sign will likely distract some drivers away from the more important driving tasks longer than a six-panel or mixed-use sign. However, driver information load profiles showed that the information load demand for nine panel logo sign is only slightly higher than six panel sign; hence the distraction levels may not be substantial enough to cause a safety concern. It was concluded that nine-panel food or gas logo sign would impart equal amount of information load on driver as that of a six-panel double-exit logo sign. The research concluded that nine-panel logo signs performed well from a human factors point of view and there is no need to prohibit the use of nine-panel logo signs.
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.