Crash test procedures for modified steel strong-post w-beam guardrail are described in various U.S. Government reports. However, these tests are always performed on new guardrail installations. The performance of guardrail with posts removed because of damage or deterioration has never been quantitatively evaluated, leading to inconsistent U.S. repair guidelines. The effect of missing posts was quantitatively evaluated using crash tests and validated finite-element models of a guardrail and a 2,000 kg (4,409 lb) pickup truck. Simulations in which one, two, or three posts were removed from the guardrail were conducted with varying impact points to evaluate the effect of missing posts. The removal of a single post compromised vehicle safety because of snagging and airborne pitching and rolling. The risk of rail rupture increased as the impact load was shifted from the posts to the rails. A single missing post in a guardrail negatively affects the crash safety and should have a high repair priority.

A new highway sign minimum retroreflectivity standard issued by the Federal Highway Administration (FHWA) is compelling agencies to evaluate how to comply while remaining within their budgets. This paper presents the results from a unique microscopic sign system simulation developed to quantitatively evaluate the effectiveness of various sign management practices. The analysis focused on three management methods—nighttime visual inspection, blanket replacement, and expected sign life—and two key sign maintenance functions, sign damage and replacement. The analysis found that sign managers should make prompt replacement of damaged signs a priority. The blanket replacement method was less cost-effective than the nighttime visual inspection method. The expected sign life method was competitive on costs with the visual inspection method while maintaining similar sign conditions. Training inspectors to be more accurate can realize further savings. Skipping inspection or replacement one year, or having an insufficient sign budget, can lead to degraded sign condition levels. The authors offer five best practices that agencies can consider when making sign management decisions.

This paper explores the relationship between sight distance parameters, crash rates, and operating speeds at low-volume single-lane roundabouts in the United States. The understanding of the interaction of design, operations, and crash performance is a step forward in the development and application of performance-based standards for roundabouts. The specific objective of this paper is to quantify the relationship between crash rates, sight distance parameters, and operating speeds to present an approach to establishing performance-based standards that highway practitioners can adopt in roundabout design. Geometric, traffic, and crash data were collected on 72 approaches to 19 low-volume single-lane roundabouts in six states. The data for these sites were broken into two groups based on the posted speed limit (at $40\mathrm{km}/\mathrm{h}$ and greater than $40\mathrm{km}/\mathrm{h}$). In addition, the associations between different sight distance parameters, crash parameters, and operating speed data were investigated. The research findings provided insight into relating the operational and safety effects of sight distance geometry at roundabouts. This research also identified a methodology that provides guidance as to the development of performance-based standards that rely on a better understanding of these relationships. In general, the research findings were consistent with previously conducted studies and indicated that exceeding sight distance thresholds increases the risk of crashes occurring. It was also found that exceeding sight distance thresholds yielded greater speed differentials between the approach and the entry to these roundabouts. The results of this research can advance the state of practice in understanding the relationships of sight distance design attributes, operational characteristics, and safety metrics for low-volume single-lane roundabouts, which is necessary to the creation of performance-based standards.

Traffic-calming measures have been widely used in urban areas, aiming sometimes to reduce vehicle flow rates but primarily to reduce speed and, hence, the number and severity of traffic accidents. The one-way priority working road narrowing (throttle) is a widely used traffic-calming technique. However, installation of such a measure close to a junction can severely affect the operation and level of service, especially for the major road movements. There is a lack of research, guidance, and design standards to inform the effective deployment of such a measure. This paper starts by providing a summary of the terms and standards used in practice for traffic-calming measures, primarily focusing on the use of throttles. The paper aims to investigate the relationship between throttle spacing ($X$) from a priority junction and the “major-to-major movement” driver’s delay for different flow levels using the S-Paramics microsimulation model. The model was calibrated and validated with field data collected from a selected site within Greater Manchester for two separate days by using camcorders. Cooperative behavior between drivers (i.e., those with priority who gave way to others) was noticed and analyzed accordingly. Different scenarios were used to test the effects on delays and queues for various parameters including throttle spacing ($X$), major-arms flow level, and reversing the direction of priority. The findings show that there is a direct relationship between throttle spacing ($X$) and the level of delay for traffic on the major arms of the junction. It is also shown that for a minor arm with two-way flow level of up to 500 vehicles per hour ($\mathrm{veh}/\mathrm{h}$), the throttle spacing should be at least 30 m. Once the flow level reaches $700\mathrm{veh}/\mathrm{h}$, the spacing should be at least 50 m, whereas for flow levels of $800\mathrm{veh}/\mathrm{h}$, the spacing should be at least 100 meters. Alternatively, consideration should be given to reversing the priority given to traffic by using MJTP (major-arm traffic has priority) operation rather than MNTP (minor-arm traffic has priority) when less throttle spacing ($X$) is required, to minimize delays to traffic on the major arms.

This paper focuses on the application of the principle of demographic gravitation to estimate link-level annual average daily traffic (AADT) based on land-use characteristics. According to the principle, the effect of a variable on AADT of a link decreases with an increase in distance from the link. The spatial variations in land-use characteristics were captured and integrated for each study link using the principle of demographic gravitation. The captured land-use characteristics and on-network characteristics were used as independent variables. Traffic count data available from the permanent count stations in the city of Charlotte, North Carolina, were used as the dependent variable to develop statistical and neural network models. Negative binomial count statistical models (with log-link) were developed as data were observed to be over-dispersed while neural network models were developed based on a multilayered, feed-forward, back-propagation design for supervised learning. The results obtained indicate that statistical and neural network models ensured significantly lower errors when compared to outputs from traditional four-step method used by regional modelers. Overall, the neural network model yielded better results in estimating AADT than any other approach considered in this research. The neural network approach can be particularly suitable for their better predictive capability, whereas the statistical models could be used for mathematical formulation or understanding the role of explanatory variables in estimating AADT.

In recent years, a growing concern related to large truck accidents has increased owing to the level of injury severity that can be sustained and to the related potential economic impact. Current studies related to large truck–involved crashes are scarce and do not address the human factors that can greatly influence accident outcomes. This study presents an analysis of data from the fusion of several national data sets addressing injury severity related to large truck–involved crashes. This is accomplished by considering human, road environment, and vehicular factors in large truck–involved crashes on U.S. interstates. A random-parameter ordered-probit model was estimated to predict the likelihood of five injury severity outcomes—fatality, incapacitating, nonincapacitating, possible injury, and no injury. The modeling approach accounts for possible unobserved effects relating to human, vehicular, and road environment factors not present in the data. Estimation findings indicate that the level of injury severity is highly influenced by a number of complex interactions between factors, and the effects of some factors can vary across observations.

Real-world vehicle fuel use and emission rates are sensitive to road grade. There is a need for a practical method for measuring road grade in combination with on-board measurement of vehicle activity, energy use, and emissions using portable emissions measurement systems (PEMS). This paper focuses on quantification of the accuracy and precision of a low-cost method using a stand-alone global positioning system (GPS) receiver with an in-built barometric altimeter. Approximately 100 one-way runs were made on each of several study routes. The sensitivity of average grade estimates to the averaging distance over which grade is estimated is quantified. The repeatability of vehicle location and distance traveled is quantified. The run-to-run variability and confidence intervals for average estimates of grade are quantified. The accuracy of the grade estimates is evaluated in comparison to LIDAR-based estimates. The low-cost method is shown to be accurate, but imprecision in the measurements leads to a need for typically at least 10 or more repeated runs, depending on the desired precision of the average estimate of grade.

For safety and energy reasons, most metro stations in China choose to install platform screen doors (PSDs), which make passengers not distribute evenly on the platform, but instead gather into clusters in front of screen doors to wait for a train. However, the traditional evaluation method considers passengers evenly distributing on platform and does not reflect the actual status of waiting passengers. In addition, the traditional method is limited to accurately describe the crowdedness level on platform and merely considers per capita space and walking freedom, neglecting the service quality in the boarding process and safety evacuation in an emergency. Subsequently, the paper introduces the new classification method of crowdedness levels, which not only considers pedestrian flow characteristics but also takes the concepts of boarding service for passengers and safety evacuation for managers into account. From the perspectives of passengers and managers, this paper defines and calculates four key indicators—per capita space, per capita longitudinal distance, boarding coefficient, and evacuation coefficient—and then classifies the crowdedness level with the $K$-mean cluster analysis method. Finally, the paper verifies the applicability and feasibility with an actual case study.

The design of urban bus transit systems aims to determine a network configuration with a set of bus lines and associated frequencies that achieve the targeted objective. This paper presents a methodology framework to formulate and solve the bus transit network design problem (TNDP). It first proposes a TNDP taking into account the travel time stochasticity. A robust optimization model is formulated for the proposed problem, which aims to minimize the sum of the expected value of the operator cost and its variability multiplied by a weighting value. A heuristic solution approach, based on $k$-shortest path algorithm, simulated annealing algorithm, Monte Carlo simulation, and probit-type discrete choice model, is subsequently developed to solve the robust optimization model. Finally, the proposed methodology is applied to a numerical example.

High-speed rail (HSR) networks require large investments, and the performance of the infrastructure is affected by varying local environments, while subject to tight layout restrictions. This paper presents a fully integrated three-dimensional model to optimize the HSR alignment at a planning scale, which sets boundaries for the final project design. The model considers mandatory and desirable specifics for the locations to link and the geometry in both the plan view and the longitudinal profile. It also allows one to define prohibited and restricted land-use areas. A computational tool has been developed that takes into account the problem specifics using a simulated annealing algorithm to optimize the problem solution. The capabilities of the model and the tool are demonstrated with the application to an intentionally simple and synthetic case study, considering construction costs and problem constraints, for which sound results are obtained. Both the model and the tool can be expanded to incorporate additional complexity, establishing the basis for real applications and for further integration of geotechnical and hydrological risk factors that affect the HSR performance.

Railroad corridors contain a large number of insulated rail joints (IRJs) that act as elements (critical to safety) in the circuitries of signaling and broken rail identification systems. IRJs are regarded as sources of excitation for the passage of loaded wheels that lead to high-impact forces. These forces in turn cause dips, cross levels, and twists to the railroad geometry in close proximity to the sections that contain IRJs, in addition to local damage to the railhead of the IRJs. Therefore, a systematic monitoring of IRJs in railroads is prudent to mitigate the potential risk of their sudden failure (e.g., broken tie plates) as a consequence of rail traffic. This paper presents a simple method of periodic recording of images using time-lapse photography and total station surveying measurements to understand the ongoing deterioration of IRJs and their surroundings. Over a 500-day period, data were collected to examine the trends in narrowing of the joint gap that is attributable to plastic deformation of the railhead edges. Data was also collected with respect to the dips, cross levels, and twists that were imparted to the railroad geometry, which is attributable to the settlement of ties (sleepers) around the IRJs. The results reflect that the average progressive settlement beneath the IRJs is larger than that under the continuously welded rail, which leads to excessive deviation of the railroad profile, cross levels, and twists.