The writers present a procedure for resource allocation among transit agencies for transit fleet management, specifically focusing on the purchase of new buses and rebuilding of existing buses. The model is formulated as a nonlinear optimization problem of maximizing the total weighted average remaining life of the fleet subject to budgetary, policy, and other constraints. The problem is solved using integer programming and its application is demonstrated through a case study using actual transit fleet data from the Michigan DOT. This proposed model is an extension of earlier research on a two-stage sequential optimization method, solved by linear programming. The proposed model has a single-stage structure designed to attain a better solution by allocating resources among different improvement options and different agencies in a single step. A comparison of the results by the two methods shows that while both approaches are viable, the single-stage approach produces better results. The proposed model, as demonstrated in the case study is considered more robust, compact, efficient and suitable for both short-term and long range planning.

Developing a procedure that yields up to the maximum margin of return for the investment requires an approach that takes into account specific safety issues and the commensurate design elements for each roadway. Kentucky’s highway agency has embarked upon an initiative tagged “practical solutions” which sets its goal toward reducing costs throughout the project development process extended into operations and maintenance of all highway facilities. This operationally defines a design procedure within the context of practical solutions and sets up the guiding principles of the approach. The most critical component of practical solutions in planning and design is the definition and clarification of the initial project concept (its specific goals and objectives) since it is the corner stone of the project and used to significantly contain the cost and impact of a project. Traditional design tends to seek as high a design speed as reasonable with the aim to reduce travel time. Practical design requires that levels of service should not be taken as absolutes but rather be viewed as starting points. Each project should be viewed as an investment and as such requires an understanding of the marginal returns to be realized. As in any financial situation, there is always a point of diminishing returns, i.e., greater investment will have no or little effect on increasing the return. The system-based evaluation of practical design in this study examined the safety and operational performance of various cross-section alternatives, based on highway capacity and highway safety manual procedures. The various alternative cross sections ranged from an improved two-lane section representing a practical solution approach to a four-lane-divided highway. A case study of a Kentucky intersection improvement project is presented that exemplifies a practical solution in practice.

This study presents a survey of deformation characteristics of the installed high-density polyethylene (HDPE) pipelines. Video and laser inspections are carried out on over 15,000 ft (4,572 m) of buried HDPE pipelines installed across the nation. Different types of deformation failure modes observed in the buried HDPE pipelines are identified in this paper. The results show that the majority of buried HDPE pipelines have deformations in excess of the commonly acceptable limits along multiple locations within each pipeline.

Future sustained economic growth of the nation very much depends on the reliability and efficiency of its highway infrastructure system. Some vehicles, such as trucks, emergency vehicles, and sport utility vehicles, often experience increasing risks of single-vehicle accidents under hazardous driving conditions, such as inclement weather and/or complicated topographical conditions. An advanced simulation-based single-vehicle accident assessment model is developed considering the coupling effects between vehicles and hazardous driving conditions, including wind gust, snow-covered or icy road surface, and/or curving. Compared to existing simulation models, the new model focuses on characterizing the transient process of accidents, introducing new critical variables on assessing the accident risks under more comprehensive hazardous driving conditions and establishing more realistic accident criteria. As a holistic deterministic model, it can be used to provide useful assessment and prevention information for traffic and emergency management. For example, it can be used to define appropriate safe driving speed limits for vulnerable vehicles under normal and extreme conditions and predict potential crash and injury risk of vulnerable drivers. Moreover, the new deterministic vehicle safety behavior simulation model lays a critical basis for future reliability-based studies of single-vehicle accident risks of vulnerable vehicles under hazardous conditions. After the model is introduced, numerical analyses on a typical truck under several representative hazardous scenarios will be conducted for demonstration purposes.

This paper presents a comparative analysis of the traffic performances of turbo-roundabouts and roundabouts in terms of capacity and delays. We chose to use a recent German procedure for roundabouts included in “Kreisel” software as our calculation procedure to determine the capacity of turbo-roundabouts. We found that the capacities of turbo-roundabout secondary entries were higher than roundabout capacities when the traffic flow in the inner lane of the circle is high and the traffic flow in the outer lane of the circle is in the low to lower-middle range. On the contrary, the capacities of the main entries to roundabouts are always higher than the capacities of the main entries to turbo-roundabouts. Taking into account the arithmetic or weighted mean behavior of the four entries, the total capacities of turbo-roundabouts, at both saturated and undersaturated conditions, are, in most cases, higher than the total capacities of roundabouts. In most of the important practical situations analyzed, delays were slightly shorter for turbo-roundabouts than for roundabouts, especially for high traffic flows in the circle lanes.

Significant service performance capabilities of high-capacity mass transit make it a remarkable part of any large metropolitan transportation system. Unfortunately it is not feasible to provide citywide direct access to high-capacity transit. Other modes of transit are used as feeders to collect and deliver passengers to high-capacity mass transit. By using feeder lines the possibility of use of high-capacity mass transit increases because the travel demand for a more extended area can be satisfied. In this research, multiple modes with various capacities and performances are used in the feeder network design based on the minimization of user, operator, and social costs. Other approaches have only used one mode (usually bus) for designing the feeder network.

This paper presents a research effort undertaken to explore the applicability of data mining and knowledge discovery (DMKD) in combination with Geographic Information System (GIS) technology to pavement management to better decide maintenance strategies, set rehabilitation priorities, and make investment decisions. The main objective of the research is to utilize data mining techniques to find pertinent information hidden within the pavement database. Mining algorithm C5.0, including decision trees and association rules, has been used in this analysis. The selected rules have been used to predict the maintenance and rehabilitation strategy of road segments. A pavement database covering four counties within the state of North Carolina, which was provided by North Carolina DOT (NCDOT), has been used to test this method. A comparison was conducted in this paper for the decisions related to a rehabilitation strategy proposed by the NCDOT to the proposed methodology presented in this paper. From the experimental results, it was found that the rehabilitation strategy derived by this paper is different from that proposed by the NCDOT. After combining with the AIRA Data Mining method, seven final rules are defined. Using these final rules, the maps of several pavement rehabilitation strategies are created. When their numbers and locations are compared with ones made by engineers at the Institute for Transportation Research and Education (ITRE) at North Carolina State University, it has been found that error for the number and the location are various for the different rehabilitation strategies. With the pilot experiment in the project, it can be concluded: (1) use of the DMKD method for the decision of road maintenance and rehabilitation can greatly increase the speed of decision making, thus largely saving time and money, and shortening the project period; (2) the DMKD technology can make consistent decisions about road maintenance and rehabilitation if the road conditions are similar, i.e., interference from human factors is less significant; (3) integration of the DMKD and GIS technologies provides a pavement management system with the capabilities to graphically display treatment decisions against distresses; and (4) the decisions related to pavement rehabilitation made by the DMKD technology is not completely consistent with that made by ITRE, thereby, the postprocessing for verification and refinement is necessary.

Remaining service life (RSL) has been defined as the anticipated number of years that a pavement will be functionally and structurally acceptable with only routine maintenance. Usually RSL is computed from pavement condition survey results. This paper presents a methodology whether RSL was estimated from pavement surface deflections. Deflection data were collected with a Dynatest 8000 falling weight deflectometer (FWD) from 1998 to 2006. Nonlinear regression procedure in the Statistical Analysis Software and Solver in Microsoft Excel were used in model development. The results showed that a sigmoidal relationship exists between RSL and center (FWD first sensor) deflection. Sigmoidal RSL models have very good fits and can be used to predict RSL at the network level based on the center deflection from FWD.

The purpose of this paper is to present a new mechanistic-empirical (ME) reflective cracking model developed for hot-mix asphalt (HMA) overlay thickness design and analysis. After reviewing existing models, the reflective cracking model based on Paris’ law of fracture mechanics was considered as the state of the practice and was selected as the basis for the ME model development in this study. The model consists of stress intensity factor and fracture properties ( $A$ and $n$ ) as the fundamental input parameters for modeling reflective crack propagation caused by both traffic loadings (bending and shearing) and thermal effects (temperature variations). For practical application, 32 SIF regression equations were developed for HMA overlays with three levels of load transfer efficiencies (10, 50, and 90%) at joints/cracks under various traffic loading spectrums (bending and shearing) based on more than 1.6 million finite element simulations and computations. For the thermal induced reflective cracking, a “hybrid” approach, similar to the Strategic Highway Research Program low temperature cracking model, was proposed. In this hybrid approach, the viscoelastic properties of the HMA mixes were considered through the thermal stress at the “far field” $\left({\sigma }_{\text{VE-far}}\right)$ , which then ties with the stress intensity factor $\left(K_{\text{thermal}}\right)$ determined through regression equations. Also, the required fracture properties ( $A$ and $n$ ) can easily be determined in the laboratory using the overlay tester that has unique features with respect to specimen size, specimen preparation, and relatively short testing time (about 15 min). Additionally, the proposed reflective cracking model was preliminarily calibrated using three HMA overlay field-case studies, and then verified using California’s heavy vehicle simulator test results. Currently, more calibration is underway, but more field performance data are definitely needed for further model calibration and verification.

Flexible overlay systems often fail before reaching their design life due to the occurrence of reflective cracking caused by stress concentrations in the vicinity of joints and cracks in the underlying pavement. In this paper, a two-dimensional finite-element fracture model of a rehabilitated airfield overlay system subjected to mixed-mode loadings was developed to obtain accurate nonarbitrary critical fracture responses in asphalt overlays placed over rigid airfield pavements. A stress-intensity factor (SIF) and $J$ -contour integral approach based on the fracture mechanics theory was selected and implemented to analyze the mechanism of airfield pavement cracking. The predicted SIFs using singular elements were verified by comparison with reference solutions based on the displacement correlation technique. The verified fracture model was applied to investigate a number of complicated environmental effects and critical aircraft gear loading conditions in an airfield overlay system associated with heavy aircraft. The gear configuration and tire pressure of a Boeing 777 aircraft were selected and applied at 12 different loading positions. Temperature-induced Mode-I SIFs were found to be extremely high, and although the magnitude of the responses would be expected to be lower with improved material models and more advanced temperature gradient modeling, the simulations nevertheless emphasized the importance of modeling temperature change in addition to gear loading in climates where daily diurnal temperature cycling is significant. A surprising finding was that aircraft gear loadings placed in the vicinity of the crack tip did not produce the most critical Mode-I stress intensities at the crack tip. Instead, counterflexure produced by gears located 3–4 m from the underlying joint produced higher stress intensities.

Reliability is an important factor in flexible pavement design to consider the variability associated with the design inputs. In this study, subgrade strength variability and flexible pavement designs are evaluated for reliability. Six existing pavement section’s design data are studied using probabilistic, AASHTO, and mechanistic-empirical pavement design guide (MEPDG). Parameters such as mean, maximum likelihood, median, coefficient of variation, and density distribution function of subgrade strength ( $R$ value) are determined. Design outputs are compared in terms of reliability and thickness using these design procedures. It is shown that the AASHTO provides higher reliability values compared to the probabilistic procedure. All the existing pavements fail in the MEPDG distress reliability such as rutting and top-down cracking reliabilities. Currently, New Mexico Department of Transportation uses a single design $R$ value to deal with variability associated with subgrade strength in flexible pavement design. It is shown in this study that single design $R$ value for a roadway section does not yield an effective design regarding target reliability, while the subsectioning procedure based on coefficient of variance of $R$ value is a better way to deal with the subgrade variability. An assessment of minimum $R$ value for making the decision of subexcavation is also presented. It is shown that increasing the minimum $R$ value for subexcavation is not always the proper solution to meet design reliability; rather it yields an inefficient design for requiring higher frequencies of subexcavation. Finally, the reliability of the flexible pavement design is evaluated by varying hot mix asphalt properties. Alternative designs are recommended for the existing pavement thicknesses by modifying material and subgrade properties to mitigate different distresses.

Railroad ballast supports heavy rail loading, prevents track deformation, and provides drainage of water from the track structure. However, over time, ballast is fouled by the breakdown of ballast aggregate and/or the infiltration of fines, which undermine the ballast functions and affect the railroad track structural capacity. Ground penetrating radar (GPR) provides a rapid, effective, and continuous way to assess railroad track substructure condition; especially ballast. However, the GPR system faces some challenges during field surveys including high radio-frequency interference from railroad communication and automation, and strong reflections from rails. In this study, appropriate techniques were used to remove the interference and reduce the strong clutter from rails to obtain clear GPR data of railroad substructure. A time-frequency method, short-time Fourier transform, was then applied to extract ballast fouling condition over depth. A field survey using multiple sets of 2-GHz air-horn antennae was conducted during summer 2007 at the Transportation Technology Center, Inc. in Pueblo, Colo. Compared to ground-truth excavation and ballast gradation analysis results, GPR was found to be an effective technique to assess railroad track ballast substructure condition.