Slab tracks are used worldwide in high-speed railways. The slab may be cast in situ, resulting in a continuous length of concrete, or it may be constructed in discrete precast sections laid end to end. According to structural characteristics of the China Railway Track System (CRTSII) slab track system, a model for dynamic analysis of vehicle-track-subgrade coupling system has been developed. Based on the model, a new type of slab track element is presented, and the associated stiffness matrix, mass matrix and damping matrix for the element are deduced. This element includes rail, rail fastening and pad, prefab slab, cement-asphalt mortar, hydraulically bonded layer, and subgrade. By means of the Lagrange equation, a numerical method for coupling the moving wheel and the rail with explicit formula is presented and the associated finite-element equation is formulated. As application examples, parameter studies on the track vibration of the slab track structure, such as stiffnesses and dampings resulting from the rail pad, CA mortar (cement-asphalt mortar) and subgrade, are investigated. To understand dynamic behavior of track transition from conventional ballast track to slab track, the effects of train speed and track stiffness on track vibration in the transition are evaluated. The obtained results show (1) reasonably chosen parameter values of the slab track structure and suitably specified stiffness of the transition will significantly improve the behavior of the track performance; (2) changing track stiffness in transition has an influence which increases with an increase of railspeed, on the vertical rail acceleration and the wheel/rail contact force; (3) smoothing of track stiffness in transition can reduce track vibration and improve the operational quality of the train. Countermeasures include long ties, additional rails, hot mix asphalt (HMA) underlayment, slab track approach, stone columns and piles to strengthen weak subgrade, rail seat pads, rubber tie mats, and other countermeasures.

New knowledge has raised a concern about the cost-ineffective design methods and the true performance of railroad prestressed concrete ties. Because of previous knowledge deficiencies, railway civil and track engineers have been aware of the conservative design methods for structural components in any railway track that rely on allowable stresses and material strength reductions. In particular, railway sleeper (or railroad tie) is an important component of railway tracks and is commonly made of prestressed concrete. The existing code for designing such components makes use of the permissible stress design concept, whereas the fiber stresses over cross sections at initial and final stages are limited by some empirical values. It is believed that the concrete ties complying with the permissible stress concept possess unduly untapped fracture toughness, based on a number of proven experiments and field data. Collaborative research run by the Australian Cooperative Research Centre for Railway Engineering and Technologies (Rail CRC) was initiated to ascertain the reserved capacity of Australian railway prestressed concrete ties that were designed using the existing design code. The findings have led to the development of a new limit-states design concept. This paper highlights the conventional and the new limit-states design philosophies and their implication to both the railway community and the public.

High-tensioned cable barriers have been introduced in the United States as a median barrier option, primarily as a result of state agencies looking for a cost-effective means by which to mitigate or eliminate cross-median crashes. This paper studies the impact of cable barriers on crash frequency and severity in a way that can be utilized in the benefit-cost estimation for new cable barrier installations where other cost components have to be included, such as right-of-way and bridge structure widening. A before-and-after analysis with negative binomial and logistic regression was applied to data obtained from eight states to investigate the impact of cable barriers on the frequency and severity of crashes on a roadway segment. Three types of crashes were investigated for both the frequency and severity of crashes: single vehicle, multiple vehicle—same direction, and multiple vehicle—opposite direction (also called cross-median or crossover crashes). These three crash categories were considered separately with the assumption, confirmed with the results, that they are all affected by the presence of a median barrier. The result indicates that an installation of cable barriers, both low- and high-tensioned, eliminates 94% of multiple vehicle—opposite direction crashes. The before-and-after analysis showed that installing cable barriers results in an increase in reported single-vehicle crashes on wide, depressed medians by about 70%. In contrast, on narrow, depressed medians, the installation of a low-tensioned cable barrier essentially results in no change in safety. For multiple vehicle—same direction crashes, there is a weak, if any, effect on safety. Considering severity, the proportion of severe crashes decreases by more than 8% when adding a lane in each direction and installing a low-tensioned cable barrier on a wide, depressed median. The reduction in the proportion of severe crashes is less than 6% when the width is reduced in addition to the widening of the roadway and installation of a low-tensioned cable barrier. The narrower median is also the only median treatment that shows a considerable change in the proportion of crashes in response to an increase in average annual daily traffic. Finally, the effect of installing high-tensioned cable barriers on severity measured with the proportion of injury and fatal crashes is small if not negligible.

Variable speed limit (VSL) systems enable freeway system managers to change the posted speed limit on a section of roadway in response to varying conditions. VSL system goals may include homogenizing traffic flow, improving safety, and/or reducing driver stress. Although it is understood that the effectiveness of VSL systems is impacted by the level of driver compliance, which itself is influenced by the extent of speed limit enforcement, very little is known about the strength of these impacts. This paper uses a simulation model to evaluate the sensitivity of the safety and operational impacts of VSL to driver compliance. Several scenarios for driver compliance were modeled using the PARAMICS microscopic traffic simulator. Findings indicated that VSL impacts are very sensitive to the level of driver compliance. Safety was shown to be positively correlated with the level of compliance, and travel time was shown to be negatively correlated. However, it was also found that the magnitude of the impact is strongly influenced by the VSL control strategy (i.e., set of rules for incrementing and decrementing the speed limits) being used. Therefore, selection of the VSL control strategy cannot be done independently of the decision regarding speed limit enforcement.

Critical gap is the threshold by which drivers in the minor stream judge whether to accept a gap. If the gap is larger than critical gap, drivers accept it and enter the intersection; otherwise, drivers reject the gap and wait for the next gap. At a priority-controlled intersection, critical gap is usually considered as a fixed value or to follow a certain distribution. The major stream and minor stream are both one-way traffic flows at the priority-controlled intersection. Vehicles in the major stream have priority to run into conflict sections, and vehicles in the minor stream can enter conflict sections during the larger gap of two successive vehicles in the major stream. The capacity of minor roads is the maximum number of vehicles that can pass the intersection during a special period under prevailing roadway, traffic, and control conditions. Under a few assumptions, the survey method of rejected gaps and accepted gaps was designed. Four new calculation models of the critical gap are proposed. The probability function of rejected gap and accepted gap can be deduced by exponential rejected proportion function. Some important relations among variables of these functions can be obtained. The typical capacity functions were improved in terms of accepted proportion function.

Unlike traditional Type I dilemma zones, where inappropriate signal timings or detector placements restrict the ability of motorists to safely proceed through the intersection or safely stop in advance, Type II dilemma zones are attributed to driver difficulties in decision making. Type II issues become more prevalent at high-speed intersections, which have greater variability in operating speeds and greater potential for serious crashes. Although several features related to Type II dilemma zones are known, inconsistency remains in the application of the boundary definitions. This research characterizes driver behavior and comprehension related to Type II dilemma zones for the purpose of defining these boundary conditions. Empirical observations of 10 high-speed signalized intersection approaches were conducted, and the analyses of the observed driver behavior resulted in an expanded understanding of how and where drivers make their decision to stop or proceed when approaching a signal. Specifically, distributions of vehicle location and driver behavior were examined using multiple boundary definitions, and in several instances the distributions of driver behaviors varied depending on the dilemma-zone definition employed.

This paper presents an innovative algorithm to calculate the displacement and stress fields within a multilayered pavement system using layered elastic theory and Hankel and Laplace integral transforms. In particular, a recurrence relationship, which links the Hankel transform of displacements and stresses at any point $P(r,z)$ within a multilayered pavement system with those at the surface point, $Q(r,0)$, is systematically derived. The Hankel transforms of displacements and stresses at any point within a multilayered pavement system can be explicitly determined using the derived recurrence relationships, and the subsequent inverse Hankel transforms give the displacements and stresses at the point of interest. Theoretical and computational verification of the proposed algorithm justify its correctness. The proposed algorithm does not use a numerical linear system solver employed in the traditional approach to solve the axisymmetric problems in multilayered pavement systems. Because of the explicitly derived recurrence relationships for displacements and stresses, the proposed algorithm provides a more rapid solution time than the stress-function-based approach utilized in existing layered elastic theory programs.