A new median treatment technique using longitudinal channelizers has been used in Florida as an alternative to the traditional permanent concrete barrier. However, the effects of the new technique on roadway safety and its economic performance have not been well documented. This paper’s intent is to present the results of a comprehensive evaluation on the safety and economic performance of the longitudinal channelizers’ median treatments with before-and-after crash data. Two types of longitudinal channelizers’ treatments—full median opening to directional median opening and full median opening to left-in only median opening—were evaluated. To account for the site selection bias, the empirical Bayesian before-and-after study method was used. The safety performance function for roadway segments with full median openings was developed with the generalized linear model to consider the negative binomial distribution of the crash counts in population entities. The targeted crash types for the longitudinal channelizers’ median treatment (the left-turn crashes) were reduced by approximately 60 and 45% in the after period for directional and left-in only median treatments, respectively. The economic performance of the longitudinal channelizers’ median treatments was quantified based on the crash analysis results from the empirical Bayesian before-and-after study. The annual cost reductions on crashes per site location were $562,321 and $94,480 for directional and left-in only median treatments, respectively. Benefit-cost ratios of 18.9–224.9 can be achieved with the implementation of longitudinal channelizers’ median treatments. Further application of longitudinal channelizers for median treatment is recommended, especially for those locations where immediate treatments for safety purpose are required.

Flexible pavement design is increasingly utilizing mechanistic-empirical (M-E) based design methods. To date, research has resulted in the development of two primary prediction models for permanent deformation on the basis of two different mechanistic-behavioral theories. An axially based model assumes that deformation is the result of axial compression, whereas a shear-based model assumes shear stresses within the asphalt layer are the primary cause of deformation. Permanent deformation is likely described by a model that incorporates both theories; however, little research exists in this area. The objective of this paper is to investigate numerous permanent deformation predictive models under the hypothesis that a model that combines both mechanistic theories reduces model form error. Improvement in the accuracy of performance predictions will allow designers to investigate novel mix designs, perform accurate reliability analyses, perform precise design optimization, and provide cost-effective designs for both initial construction and maintenance plans. Validation and comparison of numerous models through classical and Bayesian statistical methods will be achieved utilizing empirical data from the National Cooperative Highway Research Program’s (NCHRP) WesTrack project.

This paper documents recent experiences using roller-integrated compaction monitoring (RICM) technologies on hot-mix asphalt (HMA) overlay construction projects in Iowa. Recently, new special provisions (SPs) to specifications were implemented by the Iowa Department of Transportation on three projects that required the use of RICM technology for HMA compaction in the breakdown position. The bid costs for implementing the new RICM SPs are discussed in this paper. RICM data were collected and analyzed in conjunction with in situ falling weight deflectometer (FWD), nuclear density gauge, and surface temperature testing conducted on the project sites. Changes in roller compaction control value (CCV), relative compaction, and surface temperature with increasing pass count, and statistical correlations between these measurements are evaluated. RICM pass coverage information was analyzed using univariate and spatial geostatistical methods. Relationships between the FWD modulus and CCV yielded higher correlation coefficients than with relative compaction. Both the CCV and FWD modulus values were significantly influenced by the support conditions underneath the compaction layer, while relative compaction was not. Roller temperature measurements were influenced by the roller travel direction. Analysis of pass coverage information using univariate and geostatistical methods revealed significant differences between different projects. The results, analysis, and experiences documented in this paper provide information to improve future specifications and quality control or assurance guidelines for HMA construction.

The regulatory requirements limiting the physical dimensions of heavy vehicles and driving skills do not guarantee the feasibility of negotiating the tightest curves of compact roundabouts. The specific evaluations needed for the intersection and the assumed design vehicle are often achieved by setting vehicle movement trajectories via computer programs, given the possibility of changing the design parameters both quickly and economically. The basic requirement for using these programs is their reliability, but they do have some weaknesses and flaws because of necessary simplifications, without which running the simulations would not be workable. A field test based on global positioning system instrumentation was conducted to define the area covered by a heavy vehicle turning in a real compact roundabout, successively compared with the simulated swept path. The preparation and the results of the experiment are described in the present study.

An overrun is an accident/incident in which an aircraft is unable to stop within the design runway length. To minimize the adverse consequences of an overrun, the Federal Aviation Administration (FAA) requires airports to have a runway end safety-area 305 m (1,000-ft) long beyond the runway design length. However, many U.S. airports are unable to satisfy this requirement without limiting the aircraft mix using the airport. In response, the FAA permits installing an engineered materials arrestor system (EMAS) as an alternative solution. Four aircraft types are investigated in this paper for stopping-distance behavior within an EMAS, as follows: (1) B737-900ER, (2) B757-300, (3) B767-400ER, and (4) B747-400ER. Stopping distances are evaluated using a base arrestor bed configuration and base arrestor material. Aircraft strut behavior, aircraft pitch moment of inertia, and bogie weights are proprietary to aircraft manufacturing companies; therefore, approximate values for load-stroke behavior, damping, pitch moment of inertia, and bogie weights are developed in this paper. Besides the base arrestor material, a suite of five low-density concrete mixes with varying stress-strain behavior are investigated for their impact on aircraft stopping-distance. In addition, aircraft stopping-distance as a function of arrestor bed configuration is investigated.

Pavement performance models exist in various forms to cater to the pavement management agencies’ needs and resources. Well-calibrated models are needed to accurately predict future pavement conditions and to forecast and prioritize confidently the future rehabilitation and maintenance expenditures. Statistical tools are commonly used to develop the performance models. These statistical models may be impractical or misleading if they do not consider experts’ opinions. This paper presents a hybrid technique where statistical tools and expert knowledge are combined for the calibration of pavement performance models. This technique was validated using historical pavement condition data for continuously reinforced concrete pavements (CRCP) from the Texas Department of Transportation’s pavement management information system (TxDOT-PMIS). The recalibrated CRCP performance models obtained with the hybrid technique represent an improvement when compared to the current models since they merge expert opinion and statistical analysis, which better reflect field observations regarding distress initiation, distress evolution rate, and maximum allowable amount of distress growth.

Many traffic simulation software tools have emerged over the last decade and are widely used for analyzing capacity, delay, and level of service at intersections, ramps, and along arterial/freeway segments. Although these tools have shown great promise, they are expensive and the data collection and input setup is time consuming and resource intensive. Traffic engineers predominantly use one of those tools to analyze a diverging diamond interchange (DDI), also known as double crossover diamond interchange. Developing a simulation model and performing required analysis takes considerable time. Because it is not necessary to obtain a detailed traffic operational analysis of a DDI while interchange alternatives are being developed, a quick and easy evaluation procedure is warranted. In this paper, a critical lane volume (CLV)-based DDI analysis methodology is developed, which could be an appropriate tool to bridge the gap. In this methodology, two intersections or nodes of a DDI, where through-traffic movements along the arterial cross each other, are considered crucial. Understanding of the crossover movements, ramp movements, and coordination of traffic movements between the two nodes and lane configuration are used in developing the methodology. Critical movements are analyzed, compared, and logically added to obtain the CLV of the two nodes. The obtained CLV is used in deriving the level of service of the two intersections in a DDI. The paper describes the mathematical formulation and analysis procedure to evaluate a DDI. Two real-world DDIs are analyzed by using the developed method and compared with simulation results for reliability and accuracy.

The optimization of a community shuttle route plays an important role in the efficient operation of public transit microcirculation. This paper develops a solution for the optimal routing design problem with the objective of minimizing the total cost, including user and supplier costs, considering passenger traffic demand and budget constraints. The optimization variables include route and headway. To calculate the user cost, a heuristic algorithm for locating stops is presented. Then the optimized headway corresponding to a given bus route is confirmed by minimizing the total cost function. In solving the problem, a depth-first search algorithm (DFS) and a genetic algorithm (GA) are both presented. By comparing the results and the CPU time of the two algorithms, this paper demonstrated that GA is reliable and more efficient than DFS. The impacts of route length and the maximum tolerable walking distance on the cost and headway are also analyzed.

Ballastless track slab system (BTS) of China Rail Transit Summit type-II (CRTS-II) is primarily used in China’s Beijing-Shanghai high-speed railway. As a new structural form, CRTS-II has not been extensively tested, and the design and manufacturing processes of CRTS-II BTS systems is not optimized and mature for its load-carrying capacity, structural integrity, deflection, and durability. This study carried out a numerical analysis of stress and deflection responses of the CRTS-II BTS system using SAP 2000. Design parameters include stiffness of the rail fastening, thickness and stiffness of the track slab, the cement emulsified asphalt (CA) mortar cushion, and the concrete supporting layer. Deflection, maximum bending stress, and maximum shear stress of different structural components of the CRTS-II BTS system are investigated under varying design parameters, with the aim to explore an improved set of design parameters. The rail defection is only significantly impacted by the rail fastening stiffness. To reduce the high-speed rail deflection so as to mitigate riding discomfort, higher stiffness of the rail fastening is suggested. To reduce the track slab bending stresses to prevent the high-speed rail from structural failure, the following parameter design strategy can be used: higher track slab thickness, lower track slab stiffness, lower rail fastening stiffness, higher CA mortar, and concrete supporting layer stiffness. All design parameters of the BTS system have negligible influence on the maximum bending stress and shear stress of the elevated bridges. The maximum shear stress of the BTS system is relative low compared with the maximum bending stress of the BTS system, suggesting that the BTS system behaves more like a beam rather than a plate.

Among the main factors affecting road crash injuries, speed is considered as a leading cause and contributing factor. There are numerous studies linking travel speeds and road crashes. Hence, an essential part of road safety plans and interventions is devoted to speed management. However, to manage speed, actual travel speeds have to be systematically and consistently monitored and analyzed. In this study, a system for the collection and analysis of free-flow travel speeds on the road network is presented, enabling speed monitoring at the nationwide level. The paper focuses on the collection and analysis of travel speeds on different road sections. Using the information gathered through advanced technologies combined with geographical information systems, a comprehensive speed database in space and time is provided allowing visual presentation and comparison of the results. This analysis can identify the road sections with significant excesses of travel speeds relative to the speed limits. It can also serve as a baseline to evaluate the impact of various counter-measures employed to reduce speeds.

In this paper, a criterion for predicting the reliability of freeway traffic flow is presented. The idea is based on an analysis of spot speed time series divided into sequences of events of random and homogeneous traffic processes. For each process, the flow rate and density were calculated; then the relationships between parameters of spot speed processes and vehicular density were obtained. Using these relationships and a simulation procedure for the spot speed process, a formulation for predicting the reliability of traffic flow moving along the offside lane on the freeway roadway was derived. Through this formulation and the measurements of flow rate and speed, the probability of instability of the roadway under examination was calculated. Furthermore, with an inverse procedure, the capacity of a lane was estimated: setting the reliability value close to 1 and considering a 15 min interval, the resulting flow rate represented the capacity. Thus, the simulation procedure was used to provide, in real time, the incoming instability conditions on the roadway and to estimate roadway capacity for the A22 Brenner Freeway, Italy.