Two-way Highways Research Articles

Safety and Mobility Performance Comparison of Two-Plus-One and Two-Lane Two-Way Roads: A Simulation Study

Two-plus-one (2+1) highways are a special configuration of two-lane two-way (TLTW) highways with a continuous center lane that is used to alternate passing lanes. The main objective of this paper is, therefore, to evaluate the suitability of the 2+1 design for Middle East conditions as a replacement for traditional TLTW roads with higher traffic volumes or as an interim solution before transforming TLTW roads into four-lane highways. In our analysis, we considered both safety and mobility performances by comparing the 2+1 and TLTW designs. The new suggested 2+1 designs were evaluated, with the first design prohibiting overtaking in the opposite direction, while the second design permitted it. Additionally, two-speed-limit strategies, uniform speed limit (USL), and differential speed limit (DSL) were also evaluated. The results showed that the 2+1 design, which prohibited overtaking in the opposite direction, was superior to TLTW in terms of mobility and safety, while the other design compromised safety compared to TLTW. The results provide valuable information to policymakers, urban planners, and transport authorities to guide evidence-based decisions on the integration of the 2+1 design as a viable solution for sustainable and efficient transportation.

Стратегирование коммерциализации инноваций в условиях отечественной экономики данных

Professor A.G. Aganbegyan defines a new transport and logistics infrastructure as a key factor of economic growth, welfare, and transformation of Russia’s socio-economic system. This new infrastructure should include two-way highways, high-speed railways, regional airports, and major logistics centers in key transport hubs. Unfortunately, such projects have a very long payback cycle that may last up to 20–25 years. Moreover, the investments may be as high as 3 trillion rubles annually. As a result, transport and logistics suppliers alone cannot support such a large-scale initiative. Domestic logistics is currently going through all the stages from 1PL to 5PL, which places very high requirements on the multimodality of transport and logistics in physical infrastructure, software, and hardware. These processes encourage research cooperation between industries aimed at developing novel interoperable R&D solutions. Russian transport and logistics infrastructure depends heavily on the railway industry: its main operational task is to maintain passenger and cargo traffic, as well as to provide safety. Under the current sanctions, Russian railroads face the challenge of developing and scaling advanced scientific and technical reserves. Technological independence relies on end-to-end production technologies, e.g., artificial intelligence algorithms, digital twins, etc., which impose requirements on data interoperability. This article describes the potential that domestic railway enterprises have for improving commercialization of innovations and technology transfer. The authors used the theory of strategy and the methodology of strategizing developed by Professor V.L. Kvint to design several recommendations on how railroad companies may increase their economic motivation to overcome various barriers.

Traffic Safety Assessment and Injury Severity Analysis for Undivided Two-Way Highway–Rail Grade Crossings

The safety and reliability of undivided two-way highway–rail grade crossings (HRGCs) are of paramount importance in transportation systems. Utilizing crash data from the Federal Railroad Administration between 2020 and 2021, this study aims to predict crash injury severity outcomes and investigate various factors influencing injury severities. The χ2 test was first used to select variables that were significantly associated with injury outcomes. By employing the eXtreme Gradient Boosting (XGBoost) model and interpretable SHapley Additive exPlanations (SHAP), a cross-category safety assessment that offers an evidence-based hierarchy and statistical inference of risk factors associated with crashes, crossings, vehicles, drivers, and environment was provided for killed, injured, and uninjured outcomes. Some significant predictors overlapped between the killed and injured models, such as old driver, driver was in vehicle, main track, went around the gate, adverse crossing surface, and truck, while the other different significant factors revealed that the model could distinguish between different severity levels. Additionally, the results suggested that the model has varying performances in predicting different injury severities, with the killed model having the highest accuracy of 93.36%. The SHAP dependency plots for the top three features also ensure reliable predictions and inform potential interventions aimed at strengthening traffic safety and risk management practices, such as enhanced warning systems and targeted educational campaigns for older drivers.

Are you in the mood to pass? A study on the interplay of psychological traits and traffic on young drivers’ overtaking behavior on two-lane, two-way highways

Overtaking maneuvers – the passing of a vehicle traveling in the same direction through use of an opposing lane – on two-lane, two-way highways have significant implications on safety and highway performance. This research examines the interplay between young drivers’ psychological traits and traffic variables to better understand overtaking behavior. A total of 111 licensed drivers between the ages of 18 and 28 (inclusive) successfully completed four unique traffic scenarios presented in random order. In all four scenarios, the lead vehicle was a truck for which the speed and passing gap size varied. A standardized self-report questionnaire captured demographic and psychological factors including impulsiveness, mindfulness, attitude towards driving and depression. Results revealed that, irrespective of the traffic scenario, the propensity to overtake a lead vehicle is associated with lower attitudes towards rule violations and speeding. In more difficult traffic scenarios, the effects of impulsiveness and mindfulness are more pronounced. Concerning moods, young drivers with higher depressive symptoms are more likely to overtake in the most dangerous scenarios. These findings can enhance driver education campaigns and targeted curricula for young drivers promoting safe driving to lessen the social and economic burdens of high-impact crashes.

Injury severity of single-vehicle weather-related crashes on two-lane highways

Roadway safety is immensely affected during adverse weather conditions. Therefore, this study seeks to quantify such effects on the injury severity of involved drivers in single-vehicle crashes on two-way highways. This should be done by identifying risk factors and accommodating the heterogeneous impacts of these factors by accounting for the heterogeneity in means and variances of random parameters in the estimated model using seven years of police-reported crash data from 2010 to 2016 in Oregon. The study findings confirm the superior performance of the mixed logit model with heterogeneity in the means and variances in terms of statistical fit comparable to the traditional mixed logit model and mixed logit model with heterogeneity in the means only. The estimation results reveal that some factors such as female drivers, fatigued drivers, crashes in the early morning (between 4:00 am and 8:00 am), and crashes that occurred in darkness with no streetlights were found to increase serious injury outcomes. The empirical findings can offer evidence-based insights to help in decision-making and countermeasure selection that is aimed at improving safety under adverse weather conditions.

Developing operating speed models for elevated multilane urban arterials using artificial neural networks

Operating speed models help assess and evaluate geometric design consistency along successive road segments. The development of operating speed models has been mostly focused on rural two-lane two-way highways, where horizontal curvature plays a dominant role in speed prediction. The need to enhance the prediction power of operating speed models and ability to capture more complex relationships within an urban setting have motivated this investigation. This research investigates the use of artificial neural networks, to develop operating speed models for multilane urban elevated arterial roads. Variables investigated in this study included geometric/operational features of a road segment in addition to the residual impact of the characteristics of upstream segments. A data collection exercise was undertaken on two major urban elevated arterial roads in Greater Cairo Region, Egypt: 6th of October and Saft Al-Laban corridors. Speed data was extracted from Google Distance Matrix Application Programming Interface and validated using test vehicle speed data. A regression-based modeling exercise was undertaken in the preliminary investigation phase to serve as a benchmark for the intended machine learning modeling exercise. Results showed that the prediction power of the developed ANN models — capturing the residual effect of upstream speeds — outperformed regression-based ones. The best-performing model used operating speeds of two upstream segments in addition to geometric/operational features of the segment under investigation to predict the segment operating speed (the model reported MAPE of 6.7%). Outputs of this model were used in a design consistency evaluation and potential transferability exercises to further investigate the model practicality.

Impact Analysis of Smart Road Stud on Driving Behavior and Traffic Flow in Two-Lane Two-Way Highway

The smart road stud (SRS) system can improve the driver’s overtaking behavior through light guidance, which shows great potential in raising the traffic efficiency of two-way two-lane roads (TWTL). In this paper, we propose a light guidance system based on SRS and a combination of driving simulator and microscopic traffic simulation methodologies for evaluating the effect of smart road studs on a TWTL traffic flow. The driving simulation results reveal that SRSs do not only drastically alter microscopic driving characteristics but also it significantly influences drivers’ decision-making process for overtaking. The frequency of overtaking with SRS escalated by 114.58% compared to that without, with the key differential in overtaking decision patterns manifesting predominantly in the selection of distance between oncoming vehicles traveling in the opposite direction. Microsimulation results demonstrate that the implementation of a smart stud system can enhance both the safety and traffic efficiency on the TWTL roadway with limited sight.

A Novel GIS Approach for Locating No-Passing Zones and Assessing Passing Sight Distance on Two-Lane, Two-Way Highways: A Case Study of MO Route 5 in the State of Missouri, USA

A Novel GIS Approach for Locating No-Passing Zones and Assessing Passing Sight Distance on Two-Lane, Two-Way Highways: A Case Study of MO Route 5 in the State of Missouri, USA

Influence of segmentation approaches on the before-after evaluation of engineering treatments: A hypothetical treatment approach

The segmentation of highways is a fundamental step in estimating crash frequency models and conducting a before-after evaluation of engineering treatments, but the effects of segmentation approaches on the engineering treatment evaluations are not known very well. This study examined the effects of segmentation approaches on the before-after evaluation of engineering treatments. In particular, this study evaluated four segmentation approaches by applying the Empirical Bayes technique to a dataset for which the ground truth was known. Four segmentation approaches included Highway Safety Manual (HSM), Fixed (kilometre post), Fisher’s, and K-means segmentation. This study utilized a 440 km stretch of rural two-lane two-way highway in Queensland, Australia, to prepare a dataset with known ground truth. The treatment under evaluation was a hypothetical treatment, which should yield a crash modification factor (CMF) of 1. For assigning hypothetical treatment, a total of fifteen datasets were prepared, including ten datasets based on the random assignment and five datasets based on the hotspot identification method. Following the before-after evaluation using the Empirical Bayes technique, the results showed that HSM and Fixed segmentation approaches predict the ground truth in both dataset types. From random assignment datasets, the estimated CMFs using HSM, Fixed, Fisher’s, and K-means segmentation approaches deviated from the true CMF (i.e., 1) by 2.32 %, 5.30 %, 6.08 %, and 8.62 %, respectively. In the case of hotspots, the corresponding deviations of CMFs were 8.57 %, 9.37 %, 28.84 %, and 35.43 %, respectively. Overall, HSM segmentation best identified the actual treatment effect, followed by the Fixed segmentation. If the variables to define homogeneity for HSM segmentation are limited, then Fixed segmentation can yield reliable crash modification factors from the before-after treatment evaluations than the crash-based segmentation approaches.

Two-lane two-way overtaking decision model with driving style awareness based on a game-theoretic framework

Overtaking on two-lane two-way (TLTW) highways is often associated with a high risk of crashing. However, existing models of TLTW overtaking decision, either mechanism- or learning-based, cannot handle well the dynamic coupling among the interacting drivers. For accurate overtaking modelling, it is crucial to consider the uncertainties of interacting vehicle behaviours, especially their driving styles. To address these needs, we propose a TLTW overtaking decision model using a level-k game theoretic framework, which can consider the mutual influences between the ego and oncoming vehicles of different driving styles. A dataset is built based on the TLTW overtaking experiments with two instrumented vehicles, then PCA and k-means clustering are used to classify three driving styles, i.e. aggressive, normal and conservative. By comparing the model predictions with the experiment data, the statistics and case studies show that the proposed model with driving style awareness can accurately describe driver decisions in TLTW overtaking.

Overtaking risk modeling in two-lane two-way highway with heterogeneous traffic environment of a low-income country using naturalistic driving dataset

Introduction: Driver behavior related to overtaking maneuvers, which are considered a major safety risk determinant on two-lane two-way highway in low- and middle-income countries (LMIC), are an important subject of further analysis. This study evaluates safety risk in terms of nature and severity of probable conflicts during overtaking maneuvers on a bi-directional undivided two-lane highway in a heterogeneous traffic environment of a low-income country. Nature and severity of probable conflicts were defined with the application of surrogate safety proximity indicators in real-world naturalistic driving environment. Method: A risk severity model for overtaking maneuver was developed to better understand the significant factors associated with the probability of conflict and its severity during overtaking maneuver using discrete choice modeling approaches. The relevance of three alternate discrete outcome frameworks, namely multinomial logit (ML), ordered probit (OP), and mixed logit (MXL) models are addressed. The best fitted model is identified and estimated. The impact of the significant attributes was also evaluated. The study collected data from a section of two-lane highway in Bangladesh using naturalistic driving from both observational and computer vision techniques. A total of 46 explanatory variables related to overtaking maneuver are assessed. Results: Speed differential between overtaking and overtaken vehicles have a significant impact on the probability of severe conflicts. Moreover, the presence of a bus as an overtaking vehicle was found to contribute significantly to the severity of conflicts. Conclusions: The study makes substantial research contributions related to overtaking behavior and safety risk evaluation during overtaking in mixed traffic environment in low-income countries. The results can be used as a proactive tool for the evaluation of overtaking maneuvers and associated safety risk, and making policy decisions reducing safety risk during overtaking maneuver as well as overall safety, while acknowledging the limited resources and facilities in low-income countries.

A simulation-based empirical bayes approach: Incorporating unobserved heterogeneity in the before-after evaluation of engineering treatments

The Empirical Bayes approach for before-after evaluation methodology utilizing the negative binomial model does not account well for unobserved heterogeneity. Building on the Empirical Bayes approach, the objective of this study was to propose a framework to accommodate unobserved heterogeneity in before-after countermeasure evaluation. In particular, this study has proposed a simulation-based Empirical Bayes approach by applying the panel random parameters negative binomial model with parameterized overdispersion (PRNB-PO) to evaluate the effectiveness of engineering treatments. The proposed framework has been tested for the wide centerline treatment (WCLT) on rural two-lane two-way highways in Australia. The empirical analysis included 511 km of WCLT treated highways in a before-after evaluation within a time period of 2010 – 2018 and 430 km of reference sites in Queensland, Australia. The PRNB-PO models outperformed the traditional negative binomial models in terms of goodness-of-fit and prediction performance for total injury crashes, and fatal and serious injury (FSI) crashes. The simulation-based Empirical Bayes approach using the PRNB-PO model resulted in more precise estimates of crash modification factors than the standard Empirical Bayes approach. The WCLT is found to result in significant reductions in total injury crashes by 28.21% (95% confidence interval (CI) = 22.92 – 33.50%), FSI crashes by 13.90% (95% CI = 6.99 – 20.81%), and head-on crashes by 25.45% (95% CI = 14.87 – 36.03%). Overall, WCLT is an effective engineering treatment and should be considered a low-cost countermeasure on rural two-lane two-way highways.

Analysis of the Impact of no Passing Zones on Fuel Costs

The primary task of traffic and transportation planning is to improve the conditions of traffic and level of service on the entire road network. On three sections, which were analyzed in this paper, the possibility of reducing the precentage of no passing zones was noticed, by changing the horizontal signalization on the segments of road section where the clear visibility for overtaking was determined for one direction of the two-way highway. In the first part of the paper, the analysis of traffic conditions on the existing and on the newly designed variants of all three observed road sections was performed. Analysis of the level of service on the intersections that are part of this research are done in chapter 2. Increasing the speed on the newly designed section results in a reduced travel time and this leads to savings in fuel costs as shown in chapter 3. Traffic forecast for the planning 2029 is done in chapter 4, the forecasted traffic load implies future traffic volumes for which adequate capacities of the road network need to be provided. Chapter 5 is based on determination of the relationship between the benefits brought by the newly designed variant and the costs that are realized during its construction. The results of this analysis were used as input data for the economic evaluation of the project solutions, where the savings in fuel costs were analyzed.

Highway Stopping Sight Distance, Decision Sight Distance, and Passing Sight Distance Based on AASHTO Models

Highway sight distance is a measure of roadway visibility, which is an important factor in the assessment of road safety. Greater visibility can provide motorists more time to avoid crashes and conflicts, facilitating safe and efficient operation. However, poor visibility can reduce the driver’s ability to react to changing conditions and is a significant factor in roadway crashes and near collisions. A driver’s ability to view ambient roadway conditions is necessary for safe operation of a vehicle. The roadway must have sufficient sight distance that drivers have the time to react to and avoid striking unexpected objects in their path. In addition, certain two-lane, two-way highways should also have adequate passing sight distance to enable drivers to use the opposing traffic lane for passing other vehicles without interfering with oncoming vehicles. This paper presents the concept and analysis of three different types of sight distance that are considered in highway geometric design based on AASHTO models: 1) the sight distances needed for stopping, applicable to all highway travels; 2) the sight distances needed for decisions at hazardous complex locations; and 3) the passing sight distance needed on two lane highways.

Influence of Safety in Performance Assessment of Two-Lane Highways: A Critical Review

Traffic operations on two-lane roads are different from that of multilane roads because of the presence of opposing traffic. More often than not, faster vehicles get impedance from slower ones, entrapped inside platoons and delayed. The delay caused to these vehicles depends on both the flow of traffic and the proportion of slower vehicles in its composition. Drivers’ of delayed vehicles search for an acceptable gap to perform passing operations. At times, a part of drivers becomes reluctant to move in platoons, especially when such delay is long enough, and they start exhibiting risk-taking behaviour while passing impeding slower vehicles. Such attempts significantly affect operations and safety of traffic. The problem is, however, more acute when the prevailing traffic is heterogeneous with a sizable proportion of slower vehicles. The present study, thus, elucidates the need for considering both operation and safety in the performance assessment of two-lane two-way highways under such traffic situations.

Evaluating drivers’ speed choice with and without route-based warnings on approach to black spots on a rural highway

A high percentage of crashes occur at black spots of rural highways, and it is of paramount importance to employ strategies that can significantly reduce these crashes. The use of warning systems is one of the different methods of achieving this goal, and this study evaluates the effectiveness of these systems in different classes of drivers. To analyze the effects of warning systems on driver performance, three speed measures (mean speed, speed variation and speed limit violation) were applied. Forty-eight male and female drivers were categorized into three age groups, namely young (18–35 years old), middle age (36–55 years old) and elderly (above 55 years old), and they were asked to drive on a rural two-lane two-way highway in the north-west of Iran to conduct the experiment. The results indicate that middle-aged men and elderly women had the highest and lowest recorded mean speeds at black spots respectively both in the warning and non-warning states. On the other hand, young male drivers had the highest speed variations in the warning state, and middle-aged male drivers recorded the lowest variations in the non-warning state. Concerning the violation of speed limit at the black spots, young and middle-aged men had the highest number of violations in the warning and non-warning states respectively. Elderly women were found to be the most cautious group both in the warning and non-warning states. Conclusively, strategies such as changing the type and number of warnings are proposed to improve the effectiveness of the warning systems in special groups of drivers.

Effect of driving style on operating speed in crest vertical curves of two-lane highways

Models that predict the operating speed (OS) in terms of highway geometry assume that drivers are homogenous individuals. However, road users build the way they drive based on their behaviour and skills, thereby configuring a so-called driving style. The state-of-the-art literature defines at least eight driving styles that affect the OS of drivers, but OS–geometry models do not consider this aspect. The purpose of this work was to study the effect of driving styles on OS in crest vertical curves (CVCs) of two-way highways. To this end, 16 drivers were selected and classified according to their driving style, based on the multidimensional driving style inventory. Subsequently, the circulation speed of each driver was tested on 40 CVCs through a 10 Hz Global Positioning System logger installed in each vehicle. New OS–vertical geometry models were developed and classified according to driving style. It was concluded that models that do not consider driving styles conceal the sensitivity of the OS to the vertical geometry of highways. Additionally, among the different driving styles there is an OS difference of up to 8 km/h. Therefore, including the driving style variable in OS models of two-way roadways is a relevant factor.

Investigating the Effects of Mental Workload on Highway Safety

The majority of vehicle collisions occur because of human error; in fact, studies have shown that approximately 95% of collisions are caused, at least in part, as a result of human mistakes. Therefore, it is important to study the main causes of human mistakes and develop mitigation strategies to reduce, if not eliminate, these errors from occurring. In this respect, designing highways that balance mental workload is a crucial task that ensures drivers have sufficient time to make appropriate decisions. However, the quantitative relationship between mental workload and collisions is not well documented in the safety literature. Enough evidence exists to support the reasonable conclusion that safety is affected by changes in workload, but there is no quantitative evidence of this effect. Consequently, this paper tries to investigate the relation between mental workload ratings and collisions on highways using data from Alberta, Canada. Horizontal and vertical curve parameters on two-lane, two-way highways were first extracted from LiDAR and GPS data using MATLAB algorithms, and the resulting features were summarized using Civil 3D. The mental workload ratings were assigned based on the presence of four major geometric features, namely, intersections, horizontal curves, vertical curves, and changes in cross-section. The results show that mental workload has a significant effect on safety for two-way, two-lane highways. Furthermore, the findings strongly indicated the need to integrate mental workload into the design process, to not only meet the operational needs of the highway, but also ensure that the geometric layout does not mentally overwhelm drivers.

Measurement of percent time spent following on two-lane highways: an exploration of spot and space-based methodologies

Percent Time Spent Following (PTSF) is used as a key performance measure for two-lane highways as recommended by the HCM2010. PTSF is the average percent of total travel time that vehicles must travel in platoons behind slower vehicles due to inability to pass. Despite its acceptance as performance indicator, PTSF is difficult to measure directly in the field. It is therefore estimated using a surrogate measure based on the spot percent of vehicles travelling with headways less than three seconds (3 s) at a fixed point. However, the application of the 3 s headways as the sole criterion in the surrogate measure is still contentious. On the basis of definition, PTSF is both spatial and temporal variable whereas its estimation is based on fixed point. It is therefore desirable to develop a spatial measurement approach for PTSF that takes into consideration of travel time. A new method was therefore developed for spatial measurement of PTSF using a test vehicle equipped with a GPS-based speed acquisition and video recording system. This study explores the spot and spatial measurement techniques of PTSF. The indicator was then measured using the two approaches concurrently. Data for the study were sampled from 18 directional segments of two-lane two-way highways in Johor and Pahang States, Malaysia. Subsequently, the estimates from these approaches were compared. On comparing the PTSF values from the spot and space-based approaches, it was discovered the latter approach produced lower values than the former in most instances. A statistical test of difference of means at 95% confidence level indicated that the estimates from the two techniques do not differ significantly. This implies that PTSF from spot measurement do not differ much from those based spatial approach developed in this study. Finding from this effort would at least substantiate the application of the spot-based PTSF measuring technique; an issue that has been debatable. It also serves as a response to the contentious issue, which has not received the desired attention from experts previously.

Passing lane optimum length on two-lane highways

An investigation into the optimum length of passing lanes on rural two-lane highways is presented in this paper. A passing lane is a short length of added lane to improve passing opportunities on two-lane two-way highways. The study utilized field data and traffic simulation in this investigation, with field data primarily used in calibrating and validating the traffic simulation program. A sensitivity analysis was conducted using traffic level and length of passing lane as the primary variables. The level of association between the reduction in platooning and study variables was examined. Study results showed that, within the range of passing lane length investigated in this study (0.5 mi to 3.0 mi), traffic performance continued to improve with the increase in passing lane length. Moreover, for the same target improvement in performance, the required passing lane length increases with the increase in traffic volume. The passing lane optimum lengths developed in this study all varied in the range between 0.80 and 2.0 miles depending on traffic volume.