<p> Fatigue cracking is one of the complex distresses that is dependent of pavement structure, asphalt mixture properties and environmental conditions. During the last decades, many asphalt agencies have conducted significant researches to investigate the fatigue cracking characterization. However, fatigue performance is still difficult to predict not only due to models and parameters but also because this phenomenon itself is not well understood. </p><p> The key point in fatigue performance prediction is which model to use and how to find the correct parameters for the selected model by using the simplest but the most reliable testing method. The modulus is one of the primary asphalt mixture properties used for the mechanistic performance prediction of asphalt pavements. Dynamic modulus testing is a common method of measuring mixture modulus as a function of loading frequencies and temperatures. Despite the numerous researches that have been carried out to evaluate mixture stiffness, it is still necessary to establish a practical dynamic modulus test method that is compatible with the field cores which are mostly less than a few inches. One of the objectives of this dissertation is to present the results of a ruggedness study of dynamic modulus testing in indirect tension mode to evaluate the factors that are most likely to affect the final results. Specimen thickness, air void content, gauge length, test temperature, and horizontal strain level, that are the critical factors that affect the dynamic modulus of asphalt concrete, were selected for the ruggedness analysis. According to the findings, air void content was found to be a major factor that affects the dynamic modulus values. </p><p> To investigate the fatigue life of the pavement, valid cyclic fatigue testing data which truly represents the mixture behavior seems necessary besides the mixture stiffness. With regard to direct tension fatigue testing, one of the common problems that substantially influence the mixture fatigue behavior is the failure at the ends of the asphalt specimens. During testing, it was observed that as more and more material was cut from the top and bottom of the gyratory-compacted specimens, the likelihood of failure in the middle of the specimen greatly increased. Therefore, fabricating shorter test specimens that are cored and cut from taller gyratory-compacted specimens can produce test specimens that have more uniformly distributed air voids such that middle failure occurs within the gauge length of the linear variable differential transformer (LVDT) in direct tension tests. As a part of study, the optimum specimen geometry of 100 mm diameter and 130 mm height was introduced through the experimental testing and numerical simulation. </p><p> The Simplified Viscoelastic Continuum Damage (S-VECD) model, a continuum damage mechanics-based model that is known as one of the effective models, has been applied to predict the performance of asphalt concrete mixtures under different loading conditions. Besides, energy-based fatigue failure criterion (<i>G^R</i>) has been proved to be able to predict the fatigue life of asphalt concrete mixtures across different modes of loading, temperatures, and strain amplitudes. This dissertation presents the application and calibration of the L&barbelow;ayered V&barbelow;iscoE&barbelow;lastic pavement analysis for C&barbelow;ritical D&barbelow;istresses (LVECD) program which is based on both S-VECD and G^R method to evaluate 33 pavement sections from different locations inside the United States, Canada, South Korea, and China. The capability of the LVECD program to capture crack initiation, crack propagation and, the damage in the pavement sections is investigated by comparing the simulation results with the field observations. In this regard, LVECD was found to effectively predict the fatigue cracking propagation in the pavement sections since reasonable agreement was obtained between the program simulations and field observations. Finally, predicted damage-to-field cracking transfer function was developed to correlate the predictive damage to the measured cracking.</p>

<p> The increasing trend in crashes and consequent fatalities due to distracted driving is a growing safety concern in our road network. With rapid advancement in cellphone and in-vehicle technologies along with driver&rsquo;s inclination to multitasking, the number of crashes due to distracted driving are further on the rise. Some previous studies attempted to detect distracted driving behavior in real-time to mitigate this issue. However, these studies mainly focused on detecting either visual or cognitive distractions, while most of the real-life distracting tasks involve driver&rsquo;s visual, cognitive, and physical workload, simultaneously. Additionally, previous studies frequently used eye, head, or face tracking data, although current vehicles are not equipped with technologies to acquire such data. To address above issues, this driving simulator study focused on developing algorithms for detecting specific distraction tasks using only vehicle control and driving performance measures. Specifically, algorithms were developed to detect two distracting tasks &ndash; texting and eating/drinking. Three data mining techniques were explored &ndash; Linear Discriminant Analysis (LDA), Logistic Regression (LR), and Support Vector Machine (SVM). SVM algorithms found to outperform LDA and LR, which detected texting and eating/drinking distraction with an accuracy of 84.33% and 79.53%, respectively. This study may provide useful guidance to successful implementation of distracted driver detection algorithm in Vehicle to Infrastructure (V2I) and Vehicle to Vehicle (V2V) communication, as well as to auto manufacturers interested in integrating distraction detection systems in their vehicles. </p>

<p>Owners face challenges in setting priorities between potential projects to maintain, rehabilitate, and improve their infrastructure. The estimated cost of each potential project is a factor that owners use in setting priorities between projects and in developing their long-term maintenance and construction project portfolio. Owners face a dilemma: considerable effort is needed to develop accurate estimates of the cost of each project, but this effort will be wasted if the particular project is not selected for the long-term plan. They therefore need estimating methods that will enable them to develop reasonably accurate early stage cost estimates without an excessive amount of effort. These early stage estimates are ?conceptual cost estimates? and ?feasibility cost estimates.? This research examines the tools that are available to owners for performing early stage cost estimates for infrastructure projects. It then compares alternative parametric functions that could be used for that purpose, using data from public agencies in California. These functions are the linear parametric, common exponential parametric, and modified Cobb-Douglas exponential parametric models. This research tests the models on 1 common type of project, pedestrian access facility projects on highways. In the United States (US) these projects result, directly and indirectly, from the Americans with Disabilities Act (ADA) that Congress passed in 1990. On highways, they produce three types of improvement: 1. wheelchair ramps at street corners to allow people in wheelchairs to cross streets at designated pedestrian crossings, 2. wheelchair-accessible sidewalks, and 3. audible signals at signalized intersections to inform visually impaired people when a pedestrian signal is in their favor. The author developed a data set of 39 pedestrian access facility projects on state highways in California, used multiple regression analysis to find 4 best-fit versions of each of the 3 functions (i.e., 12 alternatives in all), and evaluated them using the Choosing By Advantages (CBA) method. The author then benchmarks the preferred state highway cost estimating model identified in the CBA against 10 city-street pedestrian access facility projects that had been completed by 4 cities in the San Francisco Bay Area. He finds a significant difference between the state highway project cost data and the city street project cost data, and further rationalizes that these differences have their roots in both the contracting methods used by the agencies and the fact that Caltrans prepares detailed designs while cities do only minimal design. The data suggests that there is an opportunity to increase output and lower the costs of pedestrian access projects (and perhaps other types of highway projects as well) by decreasing the Caltrans design effort and transferring more of the design effort and consequent risk to contractors. This could be tested through experimentation on selected pedestrian access facility installations. This dissertation contributes to knowledge by providing a review of the place of conceptual and feasibility estimating both with respect to the overall project timeline and with respect to the methods used. It provides specific examples of the use of the various classes of estimates in the development of highway projects, and it provides a synthesis of the research on conceptual and feasibility estimating methods, most notably of parametric estimating. It then provides specific examples of parametric estimates on pedestrian access projects on California State Highways and in San Francisco Bay Area cities. Finally, it unveils the successful use by Bay Area cities of a minimal amount of design when developing design-bid-build contracts for pedestrian access facilities. The dissertation aims to provide an approach that could be used both for project-by-project conceptual estimating prior to the start of work on highway projects and for evaluating the overall credibility of the estimates on large portfolios of highway projects.

<p> Wider bike facilities intuitively accommodate a greater number of cyclists in the same amount of time, but specific queue discharge characteristics associated with varying widths and/or types of bike facilities have not been thoroughly documented. </p><p> The focus of this research analyzed queues of cyclists at four signalized intersections in Portland, OR with varying widths on the approach and downstream intersection legs. A total of 2,820 cyclists within 630 groups of queued cyclists were observed at five different intersection layouts in Portland, Oregon. The layouts consisted of: a standard bike lane six feet wide connecting bicyclists to a standard bike lane six feet wide, a standard bike lane five feet wide connecting bicyclists to two standard bike lanes each five feet wide, a buffered bike lane 12 feet wide connecting bicyclists to a standard bike lane 6.5 feet wide, a bike box 21 feet wide connecting bicyclists to a buffered bike lane 10 feet wide, and a bike box 15 feet wide connecting bicyclists to two standard bike lanes each five feet wide. </p><p> For each configuration, the following aspects were analyzed: average headway per cyclist within each queue, the time required for queues to enter the intersection, the time required for queues to clear the intersection, the number of cyclists within queues, the width of the bicycle facilities, the approach grade, and the utilization of a bike box at the intersection approach if it was present. </p><p> The first major focus of the analysis reviewed the average headway values associated with each observed queue of cyclists. The queue size with the lowest mean of the average headway was for groups of seven cyclists with an average headway of approximately 0.8 seconds per cyclist. For queues larger than seven in size, the mean of the average headway remained relatively stable until queues of 12 in size and started to slightly increase toward approximately 1.0 seconds for queues larger than 12 cyclists. In addition, it appears that utilization of a bike box has a potential relationship with a reduced average headway as compared to queues that do not utilize a bike box. The associated reduction in the mean of the average headway was approximately 0.2 to 0.3 seconds per cyclist for queues of three or more in size. </p><p> The second major focus of the analysis reviewed the queue discharge rate associated with each observed queue of cyclists. The results appear to potentially indicate that wider bike facilities approaching an intersection, wider receiving bike facilities, or utilization of a bike box generally discharge queues of bicyclists into the intersection over a shorter amount of time as compared to facilities that are narrower or underutilized. The installation of a bike box at one of the study intersections increased the approach width from five to 15 feet and resulted in consistently lower average discharge times for all queue sizes, a reduction of greater than one second for queues of two cyclists to as much as about four seconds for queues of nine cyclists. </p><p> The third major focus of the analysis reviewed the intersection clearance time associated with each observed queue of cyclists. The results appear to potentially indicate that wider bike facilities approaching an intersection, wider receiving bike facilities, or utilization of a bike box generally clear queues of bicyclists through the intersection over a shorter amount of time as compared to facilities that are narrower or underutilized.</p><p>

<p> Louisiana currently has 30 roundabouts in operation and hundreds of roundabouts in the planning and design stage. The Louisiana Department of Transportation and Development (DOTD) is very interested in knowing the safety performance of existing roundabouts in the state. </p><p> As revealed in this paper, the safety effectiveness of a roundabout depends on its prior traffic control type, conformity to the geometric design guidelines, changes in layout of intersection, and nighttime lighting conditions. All 19 roundabouts investigated by this study demonstrated significant reduction in injury crashes because of lower operating speed, reduced right-angle collisions, and elimination of head-on and left turn crashes. Based on changes in the number of conflicting points and traffic control method, it is understandable why the most significant and consistent safety improvement was associated with the roundabouts previously controlled by stop signs on minor streets. The Crash Modification Factor (CMF), as estimated by the Empirical Bayes (EB) method, for this group of roundabouts is 0.28 with a standard deviation of 0.054. The roundabout is economically justified for its safety benefit alone based on the benefit-cost ratio analysis for this group of roundabouts. </p><p> The study did identify a few compounding factors at the individual intersections, such as questionable geometric design elements, increased number of conflicting points, unpredictable human behavior, and lack of lighting at night.</p><p>

<p> Evident similarities and links between the outcomes of traffic crashes and stranded (or constrained) mobility have been identified and are reported in this research. Generally, a high level of travel activities is an indicator of high crash exposure. However, studies have shown that the highest rates of traffic fatalities occur in low- and middle-income regions, where many citizens experience relatively low levels of motorized travel. This ironic observation reveals serious challenges facing transport mobility systems in the less privileged regions of the world. Studies on traffic crashes and mobility constraints also reveal that they both have individual and regional variations in their occurrence, effects, and severities. Consequently, the outcomes of traffic crashes and constrained mobility are serious public health concerns worldwide.</p><p> As public health problems, their study is analogous to the study of diseases and other injuries and thus, suitable for the application of epidemiological techniques. This dissertation therefore explores the use of epidemiological techniques to analyze traffic crashes and mobility/accessibility constraints from a human-centered perspective. The dissertation therefore consists of two major focus areas. The first part of the study applies widely used epidemiology/public health &ndash; based statistical tools to analyze traffic crashes with the aim of gaining better understanding of the human-centered causes and factors that influence these causes, and how these ultimately affect the severity of crashes. This part is further divided into two sub-sections. The first sub-section used latent class analysis to identify homogeneous clusters of human-centered crash causal factors and then applied latent class logit and random parameters logit modeling techniques to investigate the effects of these factors on crash outcomes. The second sub-section of the first part of the dissertation applies multilevel regression analysis to understand the effects of driver residential factors on driver behaviors in an attempt to explain the area-based differences in the severity of road crashes across sub-regions. Both studies are necessary to develop potential human-centered mitigations and interventions and for the effective and targeted implementation of those countermeasures. The second part of the study provides an epidemiological framework for addressing mobility/accessibility constraints with a view to diagnosing symptoms, recommending treatment, and even discussing the idea of transmission of constrained mobility among city dwellers. The medical condition, hypomobility, has been used to connote constrained mobility and accessibility for people in urban areas. In transportation and urban studies, hypomobility can result in a diminished ability to engage in economic opportunities and social activities, hence deepening poverty and social exclusion and increasing transport costs, among other negative outcomes. The condition is especially pronounced in poor urban areas in developing countries. The framework proposed in this study is expected to help identify and address barriers to mobility and accessibility in the rapidly growing cities throughout the developing world, with particular applicability to the rapidly developing cities in Sub-Saharan Africa. </p><p> Ultimately, this dissertation explores the application of epidemiological techniques to two major transportation problems: traffic safety and constrained mobility. The techniques presented in this dissertation provide policy makers, agencies, and transport professionals with tools for evidence-based policies and effective implementation of appropriate countermeasures.</p><p>

<p>In this research study, high plastic and medium plastic soils were used in evaluating the physical and mechanical properties of fly ash-soil Geopolymer mixtures. Sieve analysis and Atterberg limit tests were conducted to classify the soil. Class F fly ash, an industrial byproduct, was used in the alkaline environment of a mixture of sodium silicate and various concentration of sodium hydroxide to prepare fly ash based Soil-Geopolymer mixtures. The modified proctor test was conducted to investigate the moisture-density characteristics of mixtures. Based on literature search and preliminary experiments, the experimental design matrix of was developed by using various combination of fly ash content, alkaline ratio, and concentration of sodium hydroxide. Several mixtures based on the experimental design matrix were compacted, cured at elevated temperature and tested for unconfined compressive strength. Regression analysis was conducted to develop regression models to optimize and conduct sensitivity of the compressive strength in relation to mix variables of Soil-Geopolymer mixtures. Based on sensitivity analysis and UCS criteria recommended by DOTD Louisiana, two mixtures were selected for further evaluation along with Standard soil-cement mixtures. The resilience modulus, dynamic modulus, and durability test were conducted for selected Soil-Geopolymer mixtures and standard soil-cement mixtures, as recommended by LA DOTD. The result of the study showed that the alkali activated soil-fly ash mixtures fulfilled the compressive strength criteria of cement treated design (CTD) and cement stabilize design (CSD) of 150 psi and 300 psi, as recommended by LA DOTD. Also, the results indicated that Soil-Geopolymer showed satisfactory performance under compressive strength test and dynamic loading tests. Further, the Soil-Geopolymer mixtures passed wet and dry durability test criteria. Based on mechanical and durability characteristics evaluated it can be recommended that Soil-Geopolymer mixtures studied in this study has an immense potential to be used as pavement subgrade, subbase, and bases.

<p>There can be environmental problems associated with using cement to stabilize soils. Thus, a substitute for cement in the stabilization of road base/subbase is desirable. A Geopolymer can be a good alternative for cement stabilization, as geopolymer produces fewer greenhouse gasses compared to cement. Soil-RAP-Geopolymer as road base and subbase material have been investigated in this research. The standard method of soil stabilization in Louisiana is soil-cement, hence 5% and 10% soil-cement was selected for the comparison. In addition to the physical and mechanical tests, the durability test was also conducted to evaluate the long-term performance of Soil-RAP-Geopolymer mixtures developed in this study. Two different types of soils with medium and high plasticity indices from Louisiana were used. Water content was substituted with alkali at an OMC level to compact the Soil-RAP-Geopolymer at a maximum dry density. An experimental design matrix was established for developing statistical based regression models for the UCS and to optimize the mixture design. Higher FA and RAP content produced mixtures with higher strength, and hence 25% FA and 25% RAP provided the better performance in terms of mechanical properties. Optimum sodium silicate content however depended on the type of soil, and the percentage of FA and RAP in the mixture. UCS, resilient modulus, dynamic modulus and elastic modulus of the optimum mixture were found to be better than 5% and 10% of soil-cement mixtures. The optimum Soil-RAP-Geopolymer mixtures successfully passed the minimum strength criteria of CSD and CTD as used by Louisiana Department of Transportation and Development (DOTD). The durability characteristics also confirmed that the developed Soil-RAP-Geopolymer mixture could be used in the field of soil stabilization. The microstructure and morphology analysis on optimum mixtures confirmed that geopolymer was formed with FA, RAP, and soil in the presence of alkali.

About twenty percent of the U.S. National Highway System is under construction during the peak summer roadwork season. Fifty percent of all highway congestion is attributed to nonrecurring conditions and work zones are estimated to account for nearly twenty four percent of nonrecurring delay. Work zones account for two percent of roadway crashes and more than 1,000 fatalities per year. The major question on which this research focuses is: "How do work zone delineation strategies, intelligent transportation systems (ITS) technologies, and driver behavior impact traffic flow and crash potential in and around work zones?" To address this question effectively, one might consider assessing actual traffic situations under local conditions with the aid of a microscopic simulation model. Such simulation tools could be useful to individuals designing work zone deployment plans, developing work zone traffic management concepts, deciding on the use of ITS applications in work zones, and formulating alternate route strategies. In addition, such tools may improve the ability to visualize the impact of delineation and dynamic merge guidance strategies as well as to quantitatively assess the impact on delay and the occurrence of high crash potential situations in and around work zone areas. The underlying objective of this research is to improve the way researchers and practitioners are able to explain and predict traffic conditions and driver behavior as they are impacted by work zone strategies including variable message signs, static signage, tapers, arrow boards, and positive separation. Central to this research was the formulation of an algorithm that improves upon traditional car following theory by incorporating factors such as driver familiarity, adaptability, aggression, and accommodation to the changing road conditions found in work zones. The use of these concepts incorporates two notions: (1) drivers must manage interaction with both the roadway and other drivers; and (2) drivers exhibit varying preferences for early or late merges based on their willingness to respond to upcoming lane restrictions and their inclination to be passive or aggressive in forced merge situations.

Congestion is a world-wide problem in transportation. One major reason is random interruptions. The traffic network is inherently stochastic, and strong dependencies exist among traffic quantities, e.g., travel time, traffic speed, link volume. Information in stochastic networks can help with adaptive routing in terms of minimizing expected travel time or disutility. Routing in such networks is different from that in deterministic networks or when stochastic dependencies are not taken into account. This dissertation addresses the optimal routing problems, including the optimal a priori path problem and the optimal adaptive routing problem with different information scenarios, in stochastic and time-dependent networks with explicit consideration of the correlations between link travel time random variables. There are a number of studies in the literature addressing the optimal routing problems, but most of them ignore the correlations between link travel times. The consideration of the correlations makes the problem studied in this dissertation difficult, both conceptually and computationally. The optimal path finding problem in such networks is different from that in stochastic and time-dependent networks with no consideration of the correlations. This dissertation firstly provides an empirical study of the correlations between random link travel times and also verifies the importance of the consideration of the spatial and temporal correlations in estimating trip travel time and its reliability. It then shows that Bellman's principle of optimality or non-dominance is not valid due to the time-dependency and the correlations. A new property termed purity is introduced and an exact label-correcting algorithm is designed to solve the problem. With the fast advance of telecommunication technologies, real-time traffic information will soon become an integral part of travelers' route choice decision making. The study of optimal adaptive routing problems is thus timely and of great value. This dissertation studies the problems with a wide variety of information scenarios, including delayed global information, real-time local information, pre-trip global information, no online information, and trajectory information. It is shown that, for the first four partial information scenarios, Bellman's principle of optimality does not hold. A heuristic algorithm is developed and employed based on a set of necessary conditions for optimality. The same algorithm is showed to be exact for the perfect online information scenario. For optimal adaptive routing problem with trajectory information, this dissertation proves that, if the routing policy is defined in a similar way to other four information scenarios, i.e., the trajectory information is included in the state variable, Bellman's principle of optimality is valid. However, this definition results in a prohibitively large number of the states and the computation can hardly be carried out. The dissertation provides a recursive definition for the trajectory-adaptive routing policy, for which the information is not included in the state variable. In this way, the number of states is small, but Bellman's principle of optimality or non-dominance is invalid for a similar reason as in the optimal path problem. Again purity is introduced to the trajectory-adaptive routing policy and an exact algorithm is designed based on the concept of decreasing order of time.