Two-lane Rural Highways Research Articles

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.

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.

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.

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.

In Situ Study of Road Marking Durability Using Glass Microbeads and Antiskid Aggregates as Drop-On Materials

Road markings play an important role in road safety because they provide significant information to drivers about the road. For that reason, they must be replaced when they are not correctly perceived by road users. To analyse which are the main factors that affect road marking perception over time, a test section was designed in a two-lane rural highway, running actual traffic over 18 different types of markings fabricated with different combinations of drop-on materials. Chromatic coordinates, luminance, and retroreflectivity of each sample were measured during 18 months in order to study their evolution over time. The results obtained show different behaviours depending on the aggregates and application method used. An increment of the durability has been observed with the use of different layers and mixtures of glass microbeads with different sizes.

Istraživanje postotka vremena provedenog u koloni na dvotračnim izvangradskim cestama

In Bosnia and Herzegovina (B&H), two-lane rural highways make up the largest percentage of road network and accommodate almost complete traffic. Because of this, platoons are often formed and vehicle speeds are reduced. To improve the quality of traffic flow, it is necessary to define the level of service (LOS) for the existing condition and for alternative possibilities of reconstructing critical elements of the road network. According to Highway Capacity Manual 2010 (HCM 2010), for two-lane highways LOS is defined by measures of efficiency: average travel speed (ATS) for road class I and percent time spent following (PTSF) for road classes I and II. HCM assumes very high ATS values for conditions on national roads that are classified as class I according to HCM classification, and the problem is also nonuniformity of highway geometry elements, which further complicates the application of ATS in B&H. Therefore, PTSF was studied in this paper as an appropriate measure for determining the efficiency of two-lane rural highways. Researches carried out in the world show significant differences in PTSF results compared to the HCM calculations. No research on this topic has been conducted in the region and HCM is used in its original form. The above reasons were the main motive to study this topic and develop a model that would be easy to apply in practice. The survey was conducted on main roads with calculation speed of 80 km/h, because they are the most important in the two-lane road network. In this dissertation, calibration and validation of the Vissim 9 simulation software was first made based on conducted field research. The reason for application of the simulation software is that it allows simulation of different traffic conditions that occur in the field but cannot all be covered by surveying, or for testing some new traffic conditions. Based on the simulations of different traffic conditions, a new model for calculation of PTSF on two-lane rural roads (for speed 80 km/h) was obtained. The obtained PTSF calculation model was validated on another section and the obtained results proved the applicability of the model.

Evaluating Measures of Effectiveness for Quality of Service Estimation on Two-Lane Rural Highways

AbstractThe level of service on two-lane rural highways can be estimated using the percent time spent following (PTSF) and average travel speed (ATS). Because PTSF cannot be directly observed in th...

FREE-FLOW SPEED ON TWO-LANE RURAL HIGHWAYS: AN EMPIRICAL EVALUATION OF ESTIMATION MODELS

Free-flow speed (FFS); a fundamental parameter in the analysis of two-lane highways, is either estimated through direct field measurement or using analytical model. Regarding the latter approach, the Malaysian Highway Capacity Manual (MHCM) established a model for estimating FFS based on base-free-flow speed (BFFS), roadway’s geometric features and proportion of motorcycles in the traffic stream. Likewise, the Highway Capacity Manual (HCM) suggested an approach for direct field measurement of FFS; preferably, at a combined two-way flow rate not in excess of 200 veh/h. For most two-lane highways, observing a two-way flow rate of 200 veh/h or less is rarely possible. In such a case, the HCM recommended that mean speed could be observed at flow rates higher than the limiting value and adjusted accordingly based on an analytical model provided by the manual. This paper presents an empirical appraisal of the MHCM and HCM – FFS estimation models. Data for the study were collected from four directional segments of rural two-lane highways in Johor, Malaysia. A video recording intrumented test vehicle was used for observing the relevant variables needed in this study. An analysis of the obaseved data resulted in mean FFS values of 83.35 km/h and 83.03 km/h from HCM and MHCM models, respectively. FFS estimates from the two data sets were compared to ascertain the degree of their consistency or otherwise using statistical analysis. Results from statistical analysis using t-statistic at 0.05 significance level indicates that there is no statistically significant difference between the FFS estimates from the two approaches. Thus, finding from this study suggests that either of the two approaches could be used for measuring FFS; particularly, at combined two-way flow rates exceeding 200 veh/h.

Safety Evaluation of Alternative Audible Lane Departure Warning Treatments in Reducing Traffic Crashes: An Empirical Bayes Observational Before–After Study

Roadway departure crashes are a major contributor to traffic fatalities and injury. Rumble strips have been shown to be an effective countermeasure in reducing roadway departure crashes. However, some roadway situations, for instance, inadequate shoulder width or roadway surface depth, have limited the application of conventional milled or rolled in rumble strips. Alternative audible lane departure warning systems, including profile (audible) pavement markings and preformed rumble bars, are increasingly used to overcome the limitations that exist with the milled rumble strips. So far, the safety effectiveness of these alternative audible lane departure warning systems has not been extensively assessed. The main purpose of this paper is to examine the safety effect of installing profile pavement markings and preformed rumble bars. Specifically, this study developed crash modification factors for these treatments that quantify the effectiveness in reducing single-vehicle-run-off-road (SVROR) and opposite-direction (OD) crashes. Traffic, roadway, and crash data at the treated sites on 189 miles of rural two-lane highways in Texas were analyzed using an empirical Bayes (EB) before–after analysis method. Safety performance functions from the Highway Safety Manual and Texas Highway Safety Design Workbook were used in the EB analysis. The results revealed a 21.3% reduction in all SVROR and OD crashes, and 32.5% to 39.9% reduction in fatal and injury SVROR and OD crashes after installing profile pavement marking and preformed rumble bars.

Traffic Operations on Rural Two-Lane Highways: A Review on Performance Measures and Indicators

Two- lane highways constitute a large proportion of the highway system in the United States, particularly in rural areas. Performance evaluation on those highways is the basis for planning, upgrade, and improvement programs. Such evaluations are conducted using performance measures that should ideally be correlated to performance determinants on those highways. Unlike other highway facilities, two-lane highway performance is notably affected by the platooning phenomenon, which is believed to be a function of traffic level and passing opportunities. Over the last couple of decades, several studies have addressed performance measures on two-lane highways, and are mainly driven by the reported limitations of the current measures used by the Highway Capacity Manual (HCM). This review aims to summarize the performance measures that have been published in the literature or used in practice both in the United States and abroad. The review starts with an historical overview of the HCM performance measures since its inception in 1950. It then discusses the most important criteria for measures to be more effective in describing performance, before presenting the review results for measures that have been proposed in literature or reported as being used in practice. Finally, a subjective assessment of all performance measures against the set of criteria outlined in the article is presented. The review presented in this paper provides information that is valuable for practitioners and researchers in understating the alternative measures for assessing performance on two-lane highways, and the limitations and merits associated with those measures.

Effectiveness of Consistency Measures in Crash Prediction Models for Two-Lane Highways in Palestine

Crash prediction models (CPMs) are important tools to predict the safety performance of highways based on their operational and geometric characteristics. Most of these models use geometric design characteristics to predict the number of crashes. However, few studies have identified the effectiveness of geometric design consistency measures in explaining crash occurrence probability and crash prediction. Crash prediction models that incorporate design consistency measures for rural two-lane, two-way roadways in the West Bank of Palestine have been developed. This study compares the effectiveness of the resulting models with those which rely on geometric design characteristics only. Approximately 118 km length of two-lane rural highways in the West Bank was selected covering a variety of highway classifications, locations, and characteristics. Different design consistency measures were considered in the developed CPM. The generalized linear regression modeling approach was used, and different mathematical forms were tested. The research presents a quantitative comparison between CPMs that explicitly consider design consistency with the Highway Safety Manual models, which use geometric design characteristics. The study proposes an approach to identify geometrically inconsistent locations using the safety-consistency factor. The results indicate that geometric consistency measures could provide more reliable crash prediction models, thus predicting collision potential more accurately.

Examining vehicle operating speeds on rural two-lane curves using naturalistic driving data

Horizontal curves have been shown to exhibit crash rates significantly higher than comparable tangent segments. Extensive research has investigated the causes of crashes on horizontal curves, particularly the curve navigation process and driver speed selection. Research in this area has generally been limited by the nature of the data, which is often inhibited by practical constraints as to the number of locations and drivers that can be observed. This study overcomes these hurdles through the use of naturalistic driving data, providing insights on how drivers navigate and react to curves on rural two-lane highways. Nearly 10,000 vehicle traces were collected from 202 drivers on 219 horizontal curves as a part of this study. All driving traces were collected on rural two-lane highways with prevailing posted speed limits of 45 mph or 55 mph, as well as a diverse range of curve advisory speeds. Regression models are estimated via generalized estimating equations to discern those factors affecting mean speeds on curves. A log-linear relationship was found between curve radius and mean vehicle speed, with speeds relatively stable on radii of 900–1000 ft. or more, decreasing more rapidly as radii decreased below this range. Drivers were found to reduce speeds when curve advisories were present, but the magnitude of these reductions was much less than suggested by the advisory signs. Speeds were significantly lower when a W1-6 curve arrow sign was present adjusting for the curve radius. There were also some differences in speeds based on driver age and gender. Ultimately, this paper provides insights into driver curve navigation and demonstrates the potential of high-fidelity naturalistic driving data to assess speed management and geometric design on horizontal curves.

Safety Evaluation of the SafetyEdge Treatment for Pavement Edge Drop-Offs on Two-Lane Rural Roads

This study estimated crash modification factors (CMFs) for the SafetyEdge paving technique that is applied for the treatment of pavement edge drop-offs on two-lane rural highways. An empirical Bayes observational before-after evaluation based on installation data in Iowa, North Carolina, Ohio, Pennsylvania, and Florida found that the SafetyEdge treatment was associated with statistically significant reductions in fatal and injury (FI), run-off-the-road (ROR), opposite-direction (head-on and sideswipe), and drop-off-related crashes. The ROR CMF was also statistically significant for both horizontal curved and tangent sections. A disaggregate analysis examined the variation of the CMF for ROR with factors such as the travel lane width, traffic volume, presence of a horizontal curve, posted speed limit, and the pre-treatment ROR crash frequency. The results of that analysis indicated, for example, that the SafetyEdge paving technique appears to have a greater ROR safety benefit on two-lane rural roadway segments with average annual daily traffic volumes greater than 3,000 vehicles per day, relative to roadway segments with lower traffic volumes. A crash modification function (CMFunction) was calibrated with expected pre-treatment ROR crashes as the independent variable to simultaneously capture the relationship of the CMF for ROR crashes to multiple factors. An economic analysis found that the treatment is highly cost-effective.

Impact of roadway geometric features on crash severity on rural two-lane highways

This study examines the impact of a wide range of roadway geometric features on the severity outcomes of crashes occurred on rural two-lane highways. We argue that crash data have a hierarchical structure which needs to be addressed in modeling procedure. Moreover, most of previous studies ignored the impact of geometric features on crash types when developing crash severity models. We hypothesis that geometric features are more likely to determine crash type, and crash type together with other occupant, environmental and vehicle characteristics determine crash severity outcome. This paper presents an application of multilevel models to successfully capture both hierarchical structure of crash data and indirect impact of geometric features on crash severity. Using data collected in Illinois from 2007 to 2009, multilevel ordered logit model is developed to quantify the impact of geometric features and environmental conditions on crash severity outcome. Analysis results revealed that there is a significant variation in severity outcomes of crashes occurred across segments which verifies the presence of hierarchical structure. Lower risk of severe crashes is found to be associated with the presence of 10-ft lane and/or narrow shoulders, lower roadside hazard rate, higher driveway density, longer barrier length, and shorter barrier offset. The developed multilevel model offers greater consistency with data generating mechanism and can be utilized to evaluate safety effects of geometric design improvement projects.

COUNTERMEASURES TO IMPROVE ROAD ALIGNMENT CONSISTENCY OF UNDIVIDED RURAL ROADS

The research aims to assess the relationships between the crash rates and road consistency. Design consistency assessment is a tool employed by designers to improve road safety. The case study involved a rural two-lane two-way road in Southern Italy located on a flat terrain without spiral transition curves between tangent segments and circular curves. Road alignment consistency was examined in two steps: by adopting standards in force in Italy based on the design speed profile and by plotting operating speed profile to determine the area bounded by the speed profile and the average weighted speed, and the standard deviation of operating speeds for each geometric segment. Operating speed prediction model, which returns the 85th percentile of the speed distribution of the only cars under free flow conditions, right weather conditions, and lighting was adopted. A negative exponential function was performed to predict the global consistency of a road as a whole. Finally, a model for predicting the crash rate was calibrated, confirming an increase of design consistency when the crash rates decrease significantly. The consistency model represents a useful tool during the geometric design process or the evaluation process for two-lane rural highways.

Crashes and near-crashes on horizontal curves along rural two-lane highways: Analysis of naturalistic driving data

IntroductionPrior research has shown the probability of a crash occurring on horizontal curves to be significantly higher than on similar tangent segments, and a disproportionally higher number of curve-related crashes occurred in rural areas. Challenges arise when analyzing the safety of horizontal curves due to imprecision in integrating information as to the temporal and spatial characteristics of each crash with specific curves. MethodsThe second Strategic Highway Research Program(SHRP 2) conducted a large-scale naturalistic driving study (NDS),which provides a unique opportunity to better understand the contributing factors leading to crash or near-crash events. This study utilizes high-resolution behavioral data from the NDS to identify factors associated with 108 safety critical events (i.e., crashes or near-crashes) on rural two-lane curves. A case-control approach is utilized wherein these events are compared to 216 normal, baseline-driving events. The variables examined in this study include driver demographic characteristics, details of the traffic environment and roadway geometry, as well as driver behaviors such as in-vehicle distractions. ResultsLogistic regression models are estimated to discern those factors affecting the likelihood of a driver being crash-involved. These factors include high-risk behaviors, such as speeding and visual distractions, as well as curve design elements and other roadway characteristics such as pavement surface conditions. ConclusionsThis paper successfully integrated driver behavior, vehicle characteristics, and roadway environments into the same model. Logistic regression model was found to be an effective way to investigate crash risks using naturalistic driving data. Practical ApplicationsThis paper revealed a number of contributing factors to crashes on rural two-lane curves, which has important implications in traffic safety policy and curve geometry design. This paper also discussed limitations and lessons learned from working with the SHRP 2 NDS data. It will benefit future researchers who work with similar type of data.

Development of regionalized SPFs for two-lane rural roads in Pennsylvania

The American Association of State Highway and Transportation Officials’ Highway Safety Manual (HSM) contains safety performance functions (SPFs) to predict annual crash frequencies for several roadway types. When applying these SPFs in a jurisdiction whose data were not used to develop the SPF, a calibration factor can be applied to adjust the expected crash frequency estimate to statewide or local conditions. Alternatively, the HSM suggests that transportation agencies may develop their own SPFs in lieu of applying the calibration factor to the HSM SPFs. However, the HSM does not provide guidance on the appropriate level of regionalization that should be adopted for either method, even though safety performance may vary considerably within a state. In light of this, the present study considers the development of local or regionalized SPFs for two-lane rural highways within the Commonwealth of Pennsylvania. Three regionalization levels were considered: statewide, engineering district and individual counties. The expected crash frequency for each level of regionalization was compared to the reported crash frequency over an eight-year analysis period. The results indicate that district-level SPFs with county-level adjustment factors provide better predictive accuracy than the development of a statewide SPF or application of the HSM-calibrated SPF. The findings suggest that there are significant differences in safety performance across engineering districts within Pennsylvania. As such, other state transportation agencies developing SPFs or using calibration factors may also consider how variations across jurisdictions will affect predicted crash frequencies.