Browsing by Author "John R. Stone, Committee Member"

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Comparing Operation and Safety between a New Nano Interchange and Conventional System Interchange
(2008-12-19) Moon, Jae Pil; Billy M. Williams, Committee Member; John R. Stone, Committee Member; Joseph E. Hummer, Committee Chair; Nagui M. Rouphail, Committee Member
The primary purpose of this research is to estimate the capability and applicability of new nano interchange designs as they compare to conventional four-level interchanges. Nano interchanges were conceived to provide drivers with high speed and short travel distances while requiring less right of way in dense urban areas where real estate is expensive. This research consists of two tasks: (1) operational evaluation and (2) safety evaluation. The operational evaluation compares measures of effectiveness (MOEs) between nano interchanges and conventional interchanges for thirty volume scenarios comprised of varied data for through volumes, ramp volumes, and percentages of heavy vehicles. The estimations were conducted for an entire interchange and for key freeway segments. The MOEs for an entire interchange are travel time, speed, delay time, and ramp travel time; and the MOEs for key freeway segments are density, speed, and level of service. The safety estimations were made by building safety prediction models for collisions that may occur in the influence areas of ramps. These safety models are based on negative binomial distribution and quantified safety effects of traffic, geometric, and environmental factors using three statistical methods: (1) a generalized linear model with only main effect variables, (2) a generalized linear model with main effects and interaction terms, and (3) the new Hauer method model. Specifically, this study addresses the safety effectiveness of left-hand ramps, which are needed in the nano interchange designs, because the safety effects have not been well quantified in previous studies. Considering goodness-of-fit statistics such as the likelihood-ratio test, Akaike?s information criterion (AIC), ordinary R-squared values,the Miaou method, and CURE plots, the best safety models were chosen for four collision categories: (1) Total collisions of all types, (2) Severe collisions, (3) Related Total collisions,and (4) Related Severe collisions. The operational evaluation for an entire interchange shows that conventional interchanges perform better than nano interchanges for the volume scenarios tested. The analyses of key freeway segments show that most of operational difficulties for the nano interchanges are in diverging influence areas located on upgrade segments. The analyses also indicate that several merging influence areas that are connected to ramps with steeper and longer upgrades also have lower performance levels. The safety prediction model developed unique linear or non-linear relationships among traffic, geometric, and environmental factors. Left-hand ramps appear to have higher collision frequencies than right-hand ramps, and on-ramps have higher collision frequencies than off-ramps. In addition to estimating the safety effects, this study compares three modeling procedures. This research shows that the Hauer procedure sufficiently represents linear and non-linear relationships in terms of diverse functional forms by each explanatory variable, whereas a generalized log-linear model does not adequately develop linear relationships for some explanatory variables in terms of linear functional forms. However, the generalized log-linear model with interaction terms among independent variables fits to data as well as the Hauer procedure. Finally, based on these estimations, the operational and safety problems of nano interchanges are addressed in this study, and the following recommendations are made to improve the operation and safety effectiveness of the interchange: (1) deceleration or acceleration lanes could be extended; (2) a two-lane off-ramp or on-ramp for the nano interchange could be considered; and (3) left-hand ramps could be replaced by right-hand ramps.
Measuring the Effectiveness of Advanced Traveler Information Systems (ATIS)
(2008-12-19) Hu, Hyejung; Nagui M. Rouphail, Committee Chair; Billy M. Williams, Committee Co-Chair; John R. Stone, Committee Member; Jason A. Osborne, Committee Member; Xuesong Zhou, Committee Member
The objective of this study was to develop valid methodologies for addressing several limitations of the current Advanced Traveler Information Systems (ATIS) evaluation tools. This study was focused mainly on three enhancements. First, the queue propagation algorithm of the selected tool (DYNASMART-P) was modified to more realistically model traffic congestion. The author proposed the addition of transfer flow capacity and backward gated flow constraints for more accurately calculating transfer flow rate. Second, the study modeled the natural diversion behaviors of drivers who do not receive traveler information. Lastly, statistical models of user responses to traveler information were developed using binary and multinomial logit methods to understand and model the relationship between driversâ€™ socio-economic characteristics and their responses to traveler information. Among these three enhancements, the first two (improved queue propagation and natural diversion behavior algorithms) were implemented in the enhanced model. The user behavior models, however, were not implemented because their predictive power was not acceptable due to limitations in the data set. The enhanced model was applied to two case studies: 1) verifying the capabilities of the model under a recurring bottleneck scenario on I-40 corridor in the Triangle region of North Carolina, and 2) demonstrating the capability of the enhanced model to measure the effectiveness of U-Transportation (similar to the Vehicle Infrastructure Integration [VII] program in the USA) which has been under development in Korea. The first case study results showed that the improved queue propagation algorithm simulated the bottleneck queue much closer to the real data than the original model. The simulation results also indicated that the actual diversion rate under recurring congestion in the study network was very low. The results of the second case study demonstrated that the enhanced model can evaluate the network impact of new advanced technology in flooding situations and can evaluate the effect of market penetration of the communication technology.
Metaheuristics for solving the Dial-a-Ride problem
(2004-08-10) Chan, Sook-Yee Edna; Elmor L. Peterson, Committee Member; John R. Stone, Committee Member; John W. Baugh Jr., Committee Chair; Yahya Fathi, Committee Member
Many transit agencies face the problem of generating routes and schedules to meet customer requests consisting of either pickup or dropoff requests using an available fleet of vehicles. The Dial-a-Ride Problem (DARP) is a mathematical model that closely approximates the problem faced by these agencies. The problem is a generalization of the well-known Pickup and Delivery Vehicle Routing Problem or Vehicle Routing Problem with Time Window. However, due to the high level of service required by this type of transportation service, additional operational constraints must be considered. While the DARP can be solved exactly by various techniques, exact approaches for the solution to real-world problems (typically consisting of hundreds of requests) are not practical. The time required is often excessive as the problem is NP-hard. In this thesis, we develop heuristics that find high quality solutions in a reasonable amount of computer time for the many-to-many, advanced reservation, multi-vehicle, single-depot, static DARP. The objectives considered include the minimization of total travel time and excess ride time, and the problem is subjected to maximum ride time, route duration, vehicle capacity, and wait time constraints. The cluster-first route-second approach is adopted. Clustering is performed using either Tabu Search (TS) or Scatter Search (SS) while routing is performed via insertion. The class of insertion heuristics has been extensively applied to the DARP. Earlier algorithms focused on feasible insertions but recently, heuristics that allow infeasible insertions to be considered during searches have been introduced. In this research, two insertion heuristics are considered: IRAU, which assigns requests only when they are feasible, and IRDU, which assigns all requests even if they result in infeasibilities. Comparison studies show that the benefit of using a particular algorithm depends on the statistical properties of the data sets used. Overall, the algorithms generated better solutions than a previously published real-world (322-request) problem and found the optimal solutions for constructed (32-request and 80-request) problems with known optimal solutions.
Performance Analysis and Strategic Management of Longitudinal Pavement Markings
(2009-12-03) Zhang, Guanghua; Joseph E. Hummer, Committee Co-Chair; William J. Rasdorf, Committee Co-Chair; John R. Stone, Committee Member; Daowen Zhang, Committee Member
This research evaluated longitudinal pavement marking performance and developed useful degradation models for paint pavement markings which can help transportation agencies meet the pending FHWA minimum retroreflectivity requirements. The impacts of several important factors (such as directionality, pavement type and roughness) on marking retroreflectivity were evaluated. With a large dataset in hand, we determined whether these factors had significant impacts on marking retroreflectivity. Paint pavement marking centerline retroreflectivity values measured in the direction of paint striping were found to be significantly higher than the values measured in the opposite direction. The mean values of the retroreflectivity measurements collected on the plant mixed pavements were found to be significantly larger than the values collected on the bituminous surface treatment (BST) pavements. Image processing techniques were used to analyze paint pavement marking surface glass bead density. Bead density values were found to have a positive correlation with marking retroreflectivity measurements. Higher glass bead density led to higher marking retroreflectivity. The research also compared existing marking retroreflectivity degradation models. A linear mixed effects model (LMEM) was selected as most appropriate for the paint marking retroreflectivity data. LMEMs were established for paint pavement markings based on the data collected in NC. The research outcomes can help transportation agencies have a better understanding of paint pavement marking performance, which can lead to cost savings by maximizing the marking service lifecycles.