Two-lane Highways Research Articles

Horizontal and Vertical Curvature and its Effects on Driver Passing Choice

Passing maneuvers on rural two-lane highways require drivers to enter the opposing traffic lane to overtake an impeding vehicle. A successful maneuver requires the driver to correctly judge the time it will take to complete the pass, and the distance to and speed of the oncoming vehicle. Previous studies have shown that the type and speed of impeding vehicle, traffic volume, roadway cross-section, and driver characteristics influence gap-acceptance behavior, but have not considered vertical curvature or specified directionality in the horizontal curvature. This paper describes a driving simulation experiment in which these geometric, situational, and driver characteristic variables were collected for 643 passing attempts. A logistic regression model was developed to infer the effects of horizontal and vertical curvature on driver passing decisions. This study uniquely quantified that drivers were: more likely to pass if the road curved to the left than if it was straight and less likely to pass if the road curved to the right; more likely to pass if there was a sag curve than if the road was flat and less likely to pass if there was a crest curve; and less likely to pass when traveling uphill than if the road was level. As the influence of roadway geometry on gap-acceptance decisions is not currently implemented in overtaking models, the results of this study have practical implications for microsimulation of rural two-lane highways, highway design, and highway safety, and the inclusion of roadway geometry variables may improve future modeling of roadway capacity and passing locations along two-lane highways.

Safety Evaluation of Horizontal Alignment Design Consistency on Rural Two-Lane Highways

Design consistency in the context of highway and street design refers to the conformance of highway geometry to driver expectancy. Existing design policies provide guidance related to horizontal alignment design consistency. While design consistency has safety implications and is intuitively linked to roadway departure crashes, the authors are only aware of a few studies that sought to link measures of design consistency to safety performance. This study explores relationships between alternative measures of horizontal alignment design consistency and the expected number of roadway departure crashes along horizontal curves on rural, two-lane, two-way roads. The authors analyzed 854 horizontal curves on rural two-lane highways in Indiana and Pennsylvania using data obtained from the SHRP 2 Roadway Information Database (RID) 2.0. Relationships between measures of design consistency and the expected number of roadway departure crashes were explored using a negative binomial regression modeling approach. The results indicate a relationship between the frequency of roadway departure crashes on a study curve and the radii of upstream and downstream curves. The ratio of the length of upstream and downstream tangents relative to a study curve radius was also statistically significant in Pennsylvania. Such findings are intuitive given the concept of design consistency and represent an advancement to existing predictive methods in the AASHTO Highway Safety Manual, which estimate the expected number of crashes on a segment as a function of the characteristics of only that segment.

Driver Behavior Analyses of 2+1 Roads based on a Driving Simulation Experiment

The Korean government has moved forward with the application of 2+1 roads to mitigate traffic delays and offer safety improvements relative to the two-lane highway. Before beginning construction of the first 2+1 road in Korea, calls have been made to conduct driver behavior studies prior to implementing these roadway types within the existing road network. In this study, experiments using a driving simulator were conducted to assess driver behavior on 2+1 roads. The study results suggest several concepts to be integrated into 2+1 road design in Korea. First, drivers tended to decrease speed suddenly in both critical and noncritical transition zones so that lane changing information system is significantly important in 2+1 roads. Second, the speed change patterns on the 2+1 roads were different for driver ages, with greater variations in speed by older drivers. Third, the locations of speed reductions are related to the passing lane lengths. Sufficient passing lane length is necessary to increase capacity and may offer safety benefits based on the driver behavior analyses. Fourth, inappropriate design of a passing lane can lead to traffic operational problems, especially for older drivers. Finally, safety treatments including median-delineators should be considered in bad weather conditions including snow.

Modelling risky driving behaviour


 
 
 This paper aims to demonstrate that advanced technique of modelling may provide insights and improve our understanding of driver behavior in risky decision-making situations. The paper introduces a Hybrid choice model in order to explain the overtaking decision on two-lane highways, which is well known as a risky decision in the safety literature. This model integrates a latent variable model and an overtaking choice model by combining their measurement and structural equations. Specifically, the paper investigates the role of four personality latent variables: Thrill and Adventure Seeking, Boredom Susceptibility, Geographic Ability, and Driving Anger. Respondents to a web-based survey ranked their likelihood to overtake on two-lane highways; two scenarios were captured via short videos: the first presenting a straight section of a road with good visibility, and the second approaching a curve with reduced visibility. Several indicators were collected via self-reported questionnaire. Results indicate that, two out of the four personality latent variables investigated, Thrill and Adventure Seeking and Geographic Ability provide significant explanation for overtaking decision. Both of them are positively correlated with higher risky overtaking behavior. The Hybrid model, by considering latent variables alongside observable variables and attributes of the decision, enhances the comprehension of overtaking behaviour, and therefore may be deployed for explaining other decisions related to risky driving behaviour.
 
 

Speed models and criteria for assessing traffic performance on two-lane highways

In the widely used HCM and HBS assessment methods of the traffic performance of two-lane highways speed models are an essential element of the analytical methodology. Differences in the approach to analyses, as well as differing numbers of determinants taken into account and criteria used to assess traffic performance may all produce disparate results and reduce the practicality of the application of these methods. The paper compares the HCM and HBS speed models and demonstrates key differences in their approach to the impact of traffic volume, the share of heavy vehicles and longitudinal gradients of the road. The assessment of traffic performance by both methods also demonstrates significant differences in assessments, especially in more adverse road and traffic conditions. The paper will also show assumptions underlying the choice of research sites, methods of traffic research, databases and selected results of analyses as well as the impact of selected factors on speed and speed regression models.

Quantifying the Influence of Road Geometric Parameters on Road Safety (Case Study: Hawassa-Shashemene-Bulbula Rural Two-Lane Highway, Ethiopia)

Road safety depends on humans, vehicles, and highway conditions. These factors influence road safety separately or in combination. Despite these facts, the police report indicated that only a single cause of accident has been reported for a given accident in Ethiopia and the number of accidents that had been caused by road defect accounted around 1% of total accidents per year, which underestimates its contribution to road accidents. Beside these facts, only a few studies were carried out in Ethiopia on this issue. Even though dangerous road segments were identified and ranked along the same study area of this paper in our previous publication, Hawassa-Shashemene-Bulbula two-lane rural highway, the influences of road geometric parameters on road safety were not correlated along this study area. Therefore, it is imperative to clarify the relationship between the expected number of traffic accidents and the geometric conditions of the road under study to reduce accidents and provide safe driving environment. The main objective of this study was to quantify the influence of road geometric parameters on road safety. Using historical accident data, traffic data, and road data, the expected numbers of accidents were estimated by using the empirical Bayes (EB) method. Then, the expected numbers of accidents have been correlated with one or more road geometric parameters at a time. Accordingly, the identified dangerous road segments in the previous publication (DOI: 10.4236/jtts.2018.83009) were further analyzed to estimate the influence of road geometric parameters on road safety based on expected accident frequency. The result of the analysis shows that the radius of horizontal curve, superelevation, transition curve length, lane and shoulder widths were negatively correlated with the expected frequencies of accidents. Whereas the numbers of horizontal and vertical curves per segment, grade of the road, the occurrence of left turn horizontal curves with down grade and right turn horizontal curves with upgrade were positively correlated with the expected number of accidents. Therefore, it has been concluded that the influence of road geometry has significant effect on the occurrence of accidents along this study area.

The Effect of Highway Gradient on Passenger Car Equivalents (PCE) of Two-Lane Highways in Thailand

The Effect of Highway Gradient on Passenger Car Equivalents (PCE) of Two-Lane Highways in Thailand

HEADWAY MODELING IN NORTHERN IRAQI TWO-LANE HIGHWAYS

Headway is the time interval between passages of successive vehicles past a point on the highway. More than 8000 car headways were observed in 10 level and rolling terrain two-lane highways in northern Iraq to find the critical headway and headway distribution and modeling for these highways. It is found that the critical headways are ranges between 2.5 to 4.0 seconds with a suitable critical headway of 3.2 second. The best headway model consists of composite model, for free vehicles it is a shifted negative exponential distribution, while for constrained vehicles it is a lognormal distribution.

Probabilistic, safety-explicit design of horizontal curves on two-lane rural highways based on reliability analysis of naturalistic driving data

The high collision rates on horizontal curves compared to other roadway elements make them one of the most critical elements in a transportation network. In this regard, it is important to develop models to predict the safety performance of the horizontal curves. A considerable number of studies have been conducted to develop safety performance functions based on several concepts such as geometric characteristics, design consistency, reliability analysis, and comfort threshold. However, these models do not account for all horizontal curve design criteria or consider several cases such as driving in adverse weather conditions or on pavement of low available friction. This paper develops a probabilistic, safety explicit approach of horizontal curve design using reliability analysis of four design criteria: vehicle stability, driver comfort, sight distance, and vehicle rollover. Two situations were considered in the analysis: driving in clear weather (dry pavement) and raining weather (wet pavement) to develop safety performance functions for annual and five-year collision frequency. Four types of regression models, Poisson, negative binomial, zero-inflated Poisson, and zero-inflated negative binomial, were used in the analysis. The AIC, BIC, and Vuong test were used in evaluating the developed models.

Using horizontal curve speed reduction extracted from the naturalistic driving study to predict curve collision frequency

Many models have been developed to predict collision frequency and evaluate safety performance on horizontal curves. The approach used in data collection or some assumptions made in the analysis methodology might lead to inaccurate results. For example, manual data collection, equipment limitations, and field experiments involving monitoring driving behavior for a specific region for a short-term are potential sources of errors in data collection. This paper aims at overcoming some of these issues in developing models to evaluate safety performance of horizontal curves and predict the curve collision frequency. The developed models relate expected collision frequency on horizontal curves to the speed reduction from the approach tangent to the curve, which is commonly used as a major geometric design consistency measure. The methodology to achieve this objective included three tasks; data collection, evaluating and modeling the viable speed reduction parameters, and developing safety performance models to estimate collision frequency on horizontal curves. Individual drivers’ trips on 49 horizontal curves on rural two-lane highways in rolling and mountainous terrains in Washington State were extracted from the Naturalistic Driving Study (NDS) database. Models were developed to relate different speed reduction parameters to curve characteristics. These models were then applied to 1430 horizontal curves in Washington State to estimate the speed reduction parameters and relate them to collision frequency. Several safety performance models were developed which show that speed reduction, as a design consistency measure, is directly related to collision frequency on horizontal curves. Furthermore, the speed reduction parameters are more significant variables in predicting collision frequency than all curve geometric parameters.

A mini review on percent time-spent-following (PTSF) as the service measure for two-lane highways

Percent Time Spent Following (PTSF) is used by the Highway Capacity Manual (HCM) as one of the service measures to assess the level-of-service of two-lane highways since the 2000 edition. But, the problem facing to estimate this parameter is that the difficulty to measure it directly in the field. From several studies, it is known that the HCM analytical procedures applied in PTSF estimation produces inconsistent results with the 3 s surrogate measure and most of them are overestimate. This paper presents a review on estimating PTSF on two-lane highways from several studies that adopted HCM procedures.

ANN based short-term traffic flow forecasting in undivided two lane highway

Short term traffic forecasting is one of the important fields of study in the transportation domain. Short term traffic forecasting is very useful to develop a more advanced transportation system to control traffic signals and avoid congestions. Several studies have made efforts for short term traffic flow forecasting for divided and undivided highways across the world. However, all these studies relied on the dataset which are greatly varied between countries due to the technology used for transportation data collection. India is a developing country in which efforts are being done to improve the transportation system to avoid congestion and travel time. Two-lane undivided highways with mixed traffic constitute a large portion of Indian road network. This study is an attempt to develop a short term traffic forecasting model using back propagation artificial neural network for two lane undivided highway with mixed traffic conditions in India. The results were compared with random forest, support vector machine, k-nearest neighbor classifier, regression tree and multiple regression models. It was found that back-propagation neural network performs better than other approaches and achieved an R2 value 0.9962, which is a good score.

Overview of intermediate highway cross-sections

The paper presents an overview of safety and insights regarding traffic at highway intermediate cross-sections in the interurban highway network. This overview includes rigid and soft ‘one plus one’ cross-sections, passing lanes traffic and geometric characteristics, as well as criteria for widening a two-lane highway to form a divided multilane highway. The design overview of intermediate highway cross-sections includes traffic and safety warrants, design speed characteristics and cross-section infrastructure components, including elements that enhance traffic safety. These developments are partly an outcome of the new Israeli geometric design policy and controls for rural (interurban) highways.

HEADWAY MODELING IN NORTHERN IRAQI TWO-LANE HIGHWAYS

Headway is the time interval between passages of successive vehicles past a point on the highway. More than 8000 car headways were observed in 10 level and rolling terrain two-lane highways in northern Iraq to find the critical headway and headway distribution and modeling for these highways. It is found that the critical headways are ranges between 2.5 to 4.0 seconds with a suitable critical headway of 3.2 second. The best headway model consists of composite model, for free vehicles it is a shifted negative exponential distribution, while for constrained vehicles it is a lognormal distribution.

Origins of Reverse Lane Usage Using Nagel–Schreckenberg Model

On highways with two lanes, cars are requested to run on the slow lane and are allowed to run on the fast lane for overtaking. However, on real two-lane highways, we daily observe a phenomenon called "reverse lane usage", in which the flow on the fast lane exceeds that on the slow lane. The origins of the phenomenon have not been discussed clearly. In this paper, we study a two-lane extension of the Nagel-Schreckenberg model. We employ two types of lane-changing rules: a German and a Japanese type. The German type suppresses overtaking slow cars on the fast lane through the slow lane. The Japanese type, on the contrary, allows overtaking through both lanes. If two lanes allow the same maximum speed, the suppression of overtaking through the slow lane is the key for the reverse lane usage. If the maximum speed on the fast lane is faster than that on the slow lane, the reverse lane usage is observed in the Japanese type. The effects of stochasticity in lane changing, and mixing trucks and passenger cars are also discussed.

Development of crash modification factors of horizontal curve design features for single-motorcycle crashes on rural two-lane highways: A matched case-control study

Single-motorcycle crashes are overrepresented on horizontally curved segments of rural, two-lane, undivided (RTU) highways. However, the relationship between single-motorcycle crash risk and the design features of horizontal curves on RTU highways is not well-studied in existing literature. This study aims to quantify the effect of horizontal curve type and radius on the risk of single-motorcycle crashes with a matched case-control study that can address the issues of the low sample mean, aggregation bias, and uncontrolled confounders existing in the traditional cross-sectional study. In the matched case-control study, three matching factors—year, annual average daily traffic (AADT), and segment length—were selected to match controls (RTU segments without crash records) with cases (RTU segments with crash records). A total of 1601 cases and 16,010 matched controls over 11 years (2005–2015) were identified as matched-strata. A conditional logistic model was fitted on the matched-strata data to estimate the crash modification factors (CMFs) of horizontal curve design features for single-motorcycle crashes. The modeling results highlighted the interaction effects between curve type and radius on the risk of single-motorcycle crashes. Sharp (radius ≤ 1500 ft) non-reverse curves were identified as the riskiest curve design for motorcyclists, followed by sharp reverse curves and moderate (1500 ft < radius ≤ 3000 ft) reverse curves. The study also revealed that motorcyclists might take safety-compensation behaviors on sharp curves, narrow shoulders, and poor pavement conditions. Engineering and education countermeasures are suggested for comprehending curve presence and associated risk level, reducing curve entry speed, and improving safety awareness. Finally, the limitations of the study and possible solutions are discussed.

An Exploratory Analysis of Curve Trajectories on Two-Lane Rural Highways

This paper is aimed at obtaining a better understanding of driving behavior on horizontal curves of two-lane rural highways in terms of trajectories in relation to the different curve radii and directions by a driving simulator experiment. The driving simulator experiment involved 50 drivers and eight classes of curve radii, ranging from 125 m to 800 m. Overall, 2000 curve trajectories were analyzed and classified. Six major classes were defined: (1) ideal behavior, (2) normal behavior, (3) driving close to the centerline, (4) driving outside in curve approach, (5) cutting, and (6) correcting. Furthermore, 21 sub-classes were introduced to consider both lane departures and location of the corrective actions. The CATANOVA tests and Bhapkar’s tests showed that both the curve radius and the curve direction had a significant effect on the classification results. To get a clearer understanding of the effect of the curve radius and direction on curve negotiation, three macro-classes corresponding to safe, intermediate, and dangerous behavior were introduced. The safest behaviors significantly increased with the curve radius while the most dangerous behaviors significantly decreased with the curve radius. Furthermore, left curves showed a higher proportion of dangerous trajectories. Overall, it seems that the driving trajectories are a promising surrogate measure of safety as highlighted by the correlation between the trajectories identified as dangerous and the radii of the curves.

Operational Considerations of Passing Zones for Two-lane Highways: Spanish Case Study

The U.S. Highway Capacity Manual (HCM 2010) methodology is used in Spain to evaluate traffic operation and quality of service. In two-lane undivided highways, the effect of limiting where drivers could pass slower vehicles, or passing restrictions, is considered through the percentage of no-passing zones. This measure does not account for how passing opportunities are distributed along the road. The objective of this research was to evaluate the effect percentage of no-passing zones and average passing zone length on a two-lane highway and, if significant, incorporate them in the analysis methodology,. The TWOPAS microsimulation program was calibrated and validated to the Spanish conditions. Passing restrictions had little effect on average traffic speed (ATS), with differences lower than 6 km/h between a road segment with no passing restrictions and a road segment with a passing restriction on 100% of its length. Conversely, passing restrictions can increase the percent time spent following (PTSF) up to 30%. Increasing the passing zone length beyond 2,000 m does not improve PTSF. The new models could be used to better estimate traffic operation on Spanish two-lane highways.

Modeling Geometric Design Consistency and Road Safety for Two-Lane Rural Highways in the West Bank, Palestine

This study investigates the effect of geometric design consistency on road safety in the West Bank. Studies have shown that operating speed, vehicle stability, alignment indices, and driver’s workload are the common consistency measures that might affect safety. A total of 118-km two-lane rural highways in the West Bank, Palestine, were studied based on limitations of available data. Comprehensive geometric and operating data for the selected highways obtained from field survey, maps, and official sources were used to investigate the effect of design consistency measures on road safety. Crashes for years 2008–2012, totaling 263, were used for model development using the generalized linear regression approach. Tested models were statistically significant at 95%, and adopted models showed acceptable levels of goodness of fit. The recommended model performed well across additional highway sections, additional years of data, validation of algorithm, and “%error” with a high linear correlation. The study adds to the evidence that several geometric design consistency measures contribute to roadway safety. The significant measures for the two-lane rural highways in the West Bank were segment length, traffic volume, difference between operating and design speeds, absolute difference in the 85th percentile speeds between successive design elements, and the ratio of individual curve radius to the average radius. The practical implication of this study, in addition to being able to predict crashes based on the recommended measures, highway designers should pay careful attention to inconsistent designs of two-lane rural highways to reduce their crash frequency.

Operating speed prediction models for tangent sections of two-lane rural highways in Oklahoma State

ABSTRACTIn this study, geometric features (e.g. road and shoulder width), pavement characteristics (e.g. shoulder type, skid number, and international roughness index), and traffic parameters (e.g. posted speed limit and average daily traffic) were extensively analyzed to identify the significant predictors and develop better-fit 85th percentile speed prediction models for the tangent sections of two-lane rural highways. Three models, representing all highways, lower speed limit highways, and higher speed limit highways, were developed using stepwise multiple linear regression analysis. About 80% data from 251 locations in the State of Oklahoma, United States, was used in model development and 20% for validation. The all highways model is the best-fit among the three. Two most significant parameters of this model are posted speed limit and skid number. Additionally, international roughness index is significant in the higher speed limit highway model. The lower speed limit highway model depends only on the posted speed limit.