Journal of Transportation Engineering, Part A: Systems

The geometric elements of the road, such as tangents and curves, play a vital role in road safety because significant crashes are reported on the horizontal curves and tangent-to-curve transitions. Literature reveals that inconsistent geometric design of roads violates driver’s expectation of operating speed leading to crashes. For safe manoeuver, it is necessary to achieve consistent operating speed with road geometry based on the driver’s expectations rather than the designer’s perception. Estimation of reliable operating speeds in the design phase will help to design safer road alignments. Several past studies developed operating speed models on the curves and tangent-to-curve transitions. However, these models used spot speed data with the assumption that the constant speed persists on the horizontal curves and entire deceleration/acceleration occurs on the approach/departure tangents. In this study, an instrumented vehicle with a high-end GPS (global positioning system) device was used to obtain the continuous speed profiles for passenger cars which resulted in reliable and robust speed prediction models for a tangent, curve, and tangent-to-curve. The study also establishes a relationship between the differential of the 85th percentile speed $(\mathrm{\Delta }{V}_{85})$ and 85th percentile speed differential $({\mathrm{\Delta }}_{85}V)$. The analysis results revealed that $\mathrm{\Delta }{V}_{85}$ underestimates ${\mathrm{\Delta }}_{85}V$ by $5.32\mathrm{km}/\mathrm{h}$, and ${\mathrm{\Delta }}_{85}V$ predicted the actual speed reduction from tangent-to-curve transitions. Statistical analysis results showed low errors, variations, and strong correlation of the proposed models with the field data. The models developed in the present study were validated and compared with various other models available in the literature. The comparative study highlights the importance of using continuous speed profile data to calibrate the operating speed models.

This study presents an investigation regarding the critical contributing factors in pedestrian spatial violations based on field observation of 15,090 samples at 14 roadway segments in Shanghai, China. A violation prediction model was applied to predict the impacts of roadway geometry design and traffic on the number of violations, and a real-time pedestrian violation prediction model was used to predict whether a pedestrian would spatially violate. For the violation prediction model, a Bayesian Poisson-lognormal model was used, and for the real-time pedestrian violation prediction model, a Bayesian logistic regression model was adopted. Then, random forest was employed to rank the importance of factors that are significant in violation prediction. The results showed that the presence of median, land use type, and number of lanes are the most significant variables in spatial violation. The findings of this study can provide a basis for traffic practitioners, researchers, and authorities to analyze the reasons for pedestrians’ spatial violations and develop guidelines for crossings design.

For urban rail transit (URT) operation and management, it is important to accurately estimate the spatial and temporal passenger flow distribution spreading all over the network. Unfortunately, a literature review shows that the existing simulation-based methods and dynamic assignment methods are not able to satisfactorily achieve the goal. Therefore, this paper proposes a train operation diagram–based equilibrium model to estimate the spatial and temporal passenger flow distribution in a URT network. First, a space-time URT network is constructed based on the train operation diagram, and then an equilibrium passenger flow assignment model is proposed for a URT system. Factors including travel time, transfer time, in-train congestion, and station congestion are considered. An improved shortest-path algorithm for the space-time URT network is presented, in which the transfer constraints are fully considered. Finally, the proposed model and algorithm are verified and analyzed by using a numerical example and are also demonstrated in the Beijing URT network. The proposed model, which is based on the train operation diagram and with the consideration of transfer constraints, is beneficial to estimating passenger flow within a URT network and to managing URT.

The mainline freight train derailment rate of major railroads in the United States declined 49% from 2006 to 2015. Nevertheless, derailments remain the leading cause of major railroad accidents. Identification and quantification of the types of train accidents, the trackage where they occur, and the causes having the greatest effect on train safety and risk is critical to determine the most effective strategies for further improvement. Federal Railroad Administration data were used to quantify factors contributing to the declining accident trend. Most derailment causes declined with the greatest reductions in broken rails and welds, track geometry, and other axle and journal defects. Of the few causes that increased, extreme weather was the largest. An updated statistical model of the relationship between track class, traffic density, method of operation, and derailment rate is also developed. Derailments declined uniformly with respect to all combinations of the three factors, indicating a broad general decline across the network. The new model also provides up-to-date derailment rate estimates for use in risk analysis of railroad freight and hazardous materials transportation.

It has been an engineering practice that highway agencies collect traffic data using highway traffic monitoring techniques such as permanent traffic counts (PTCs) and weigh in motion (WIM). This research used the WIM traffic data collected for $6\mathrm{years}$ from one of six WIM sites installed and operated in the Alberta provincial highway network to develop a winter weather dummy variable model. Five other sites were used for a spatial transferability test of the estimated model. Few past studies have tested empirically whether a winter weather model developed for one site can be transferred spatially to other locations. A goal of this paper is to develop a winter weather dummy variable model using winter season traffic and weather data and then test its spatial transferability by applying the model to other geographically dispersed locations. A total of 16,746,310 vehicular records collected for $6\mathrm{years}$ spanning from 2005 to 2010 at a WIM site on a commuter road near the City of Leduc, Alberta, Canada, were used to calibrate a model. Three vehicle classes such as total traffic, passenger cars, and truck traffic were classified from raw WIM data and used for model development. Using four types of model structures differentiated from the initially developed model for each vehicle class, this research performed spatial transferability. This research shows that the developed dummy variable model can be successfully spatially transferred to the other five WIM sites. More accurate traffic estimates can be made during winter seasons by using other model structures for each vehicle type.

The design of an underground metro alignment in an urban area is complex and challenging. The metro alignment constantly invades districts with high-density buildings and specially planned districts, which results in large additional expenses due to reconstruction, land requisition, demolition, vibration absorption, and environmental protection. This paper presents a method for the optimization of the horizontal alignment between metro stations to minimize the overall cost. The proposed method includes three steps: (1) low-cost path search, (2) initial horizontal alignment generation, and (3) horizontal alignment optimization. First, an augmented rapidly exploring random-tree connect (RRT-connect) algorithm is developed to search for a low-cost path, in which the buffer zone of the low-cost path defines the corridor constraint of the horizontal alignment optimization. Subsequently, based on the low-cost path, an initial horizontal alignment is generated that determines the number of design variables, i.e., intersection points. Next, within the corridor constraint, the method optimizes the intersection point coordinates and curve radius on the initial horizontal alignment using a differential evolution (DE) algorithm. A real-world metro line was studied to verify the effectiveness of the proposed optimization approach.

Crashes are one of the major causes of traffic delays. It is therefore essential to clear crashes as quickly as possible. However, adverse weather conditions, especially rainy conditions, could potentially influence crash clearance duration. This study aimed at evaluating the effect of rainy conditions on the clearance duration of crashes on freeways. The specific objectives were (1) to estimate the duration of rainfall during the crash clearance time, and (2) to evaluate the impact of crash-related, spatiotemporal, and responding agencies’ attributes on the crash clearance time during rainy conditions. The analysis was based on 2014–2016 crash data and hourly rain data on a network of freeways in Jacksonville, Florida. The study estimated the rainfall duration during the crash clearance time. Hazard-based models and bootstrap resampling method were used to investigate factors that influence the crash clearance time. The results indicated that the level of the impact of a crash, the rainfall duration, the time of day, and the day of the week significantly affect crash clearance time during rainy conditions. The study results can assist incident management agencies in advancing strategies to reduce crash clearance time during adverse weather conditions.

The paper aims to estimate the corridor capacity of a bus rapid transit (BRT) system by using a revised failure rate approach. The two important factors that influence capacity, which are explored in the present study, are the bus lost time and the failure rate. These factors, along with other factors, were estimated for stops of a selected corridor in the Ahmedabad Bus Rapid Transit System in India. The bus lost time, i.e., the time taken by the first passenger to board the bus, was used to estimate the dwell time and calculated using field data. However, the Transit Capacity and Quality Service Manual provides a default value of the bus lost time for a three- and four-berth stop. But unfortunately, no such value is available for a two-berth stop, and hence, it was estimated using bus stop videography data. Before applying the failure rate approach, it is important to note that, as per literature, two types of capacities are estimated for a transit system, i.e., the operational and maximum capacity. The former is calculated using the field estimated failure rate, whereas the latter is generally assessed using a maximum failure rate of 25% in the case of a conventional stop. Because the present study deals with the exclusive bus system, a maximum failure rate value for a two-berth BRT stop was computed as 29%. The bus stops in the present study were not overtaking stops; hence, the reduction in efficiency of the first birth due to the second berth being occupied was computed as 17%, and this value was estimated using trajectory plots. Based on the proposed methodology, the upstream and downstream capacity of the selected bus corridor was estimated at 136 and $137\mathrm{buses}/\mathrm{h}$, respectively.

This paper investigates the status of lateral stability of a ballasted curved track, which is carried out under four loading scenarios in terms of the factor of safety against displacement as the indicator. Then, the Prud’homme limit is introduced to analyze the equilibrium between the lateral load on a track and the lateral resistance by a track. Finally, a tie spacing formula for sharp curves is recommended to ensure lateral stability. The work has the potential to estimate the critical temperature differential for buckling of a curved track by using a factor of safety of unity in the formula derived for an unloaded track, as a factor of safety of unity represents a unstable equilibrium.