Two-lane Roads Research Articles

A model for estimating advisory speeds for horizontal curves in two-lane rural roads

Horizontal curves are designed using a design speed, which is the speed used to determine the geometric features of highways. In sharp curves, drivers sometimes exceed the design speed. Depending of the difference between design speed and operating speed, drivers can face risky situations, which can be mitigated using signs informing drivers of advisory speeds. Advisory speeds at the horizontal curves are normally estimated as a function of the lateral acceleration for a maximum driving speed, at which comfort is low. This paper proposes an analytical model to estimate advisory speeds based on ball-bank readings and consistency concepts. Field data were obtained using a digital ball-bank indicator, an accelerometer, and a GPS logger. Readings were obtained on 24 test sections at speeds between 40 and 110 km/h. The model proposed yields an advisory speed value and a limit ball-bank angle that require consistent behavior of drivers.

Dynamical Control Strategy on Two-lane Roads with Speed Limitations under Intelligent Transportation System

Dynamical Control Strategy on Two-lane Roads with Speed Limitations under Intelligent Transportation System

Risk-type density diagrams by crash type on two-lane rural roads

The research presented here aims to plot density diagrams per road crash risk type to identify all possible scenarios where driving is less than safe. The starting point was the prediction of injury crash rate on horizontal homogeneous segments of two-lane rural roads for three main injurious crash types (head-on/side collisions, rear-end crashes, and single-vehicle run-off-road crashes) as observed on the network. A careful analysis of the database shows that a wide variety of factors appear to be influenced or associated with the crash dynamic, as follows: the road scenario (combination of infrastructure and environmental conditions found at the site at the time of the crash), mean lane width, the horizontal curvature indicator (measurement of the curvature change rate), and mean speed. Crashes recorded from 2003 to 2010, of which 1597 were injurious, and 645 resulted only in damage to property, were analyzed on more than 3700 km of road network in Southern Italy. Generalized estimating equations with a negative binomial distribution were implemented. Risk-type density charts were plotted to thoroughly identify all possible combinations of existing explicative variables producing hazardous conditions on the road. The different shades in the diagrams represent different ranges of injurious crash rates: the white band shows low levels, while a black band shows high values. It is not possible to consider working on an explanatory variable to reduce hazardous conditions on the road network without also considering how this variation might affect the influence of the remaining explanatory variables on crash phenomena and, consequently, on the predictive model. The risk maps make it possible to keep under control in a simple and immediate approach the way each variable as a result of variations of a part or of all.

Delay Analysis for Sparse Vehicular Sensor Networks with Reliability Considerations

This paper addresses the relation between message delivery delay and reliability for the communication between a vehicle and a road side unit (RSU). We focus on sparse vehicular sensor networks (VSNs), where timely message delivery and reliable transmission are of significant importance. We present a mathematical framework for the message delivery delay distribution for a two-lane road, where vehicles in one direction act as message carriers for the ones in the other direction and have the freedom to leave the road from randomly distributed road junctions with a certain probability. Packet generator vehicles store the original packets till meeting an RSU while sending multiple copies of each packet to packet carrier vehicles. Our analysis offers an analytical tool for an intelligent transportation system (ITS) service provider to determine the minimum RSU density required to cover a road for meeting a probabilistic requirement of the message delay. Extensive computer simulation results show the accuracy of our analysis and clearly indicate the relation of packet delay and the number of packet replicas.

Relationship between Predicted Speed Reduction on Horizontal Curves and Safety on Two-Lane Rural Roads in Spain

According to different studies, speed reduction is considered one of the major factors in contributing road safety. For that reason, several guidelines have been recommended for maximum desirable speed reductions from tangents to horizontal curves and for maximum differentials between design and operating speeds on horizontal curves. The Interactive Highway Safety Design Model (IHSDM) Design Consistency Module presents an analysis of the relationship between speed reduction and crashes for horizontal curves on U.S. two-lane rural highways. This paper presents the relationship between speed reduction and crashes for horizontal curves on Spanish two-lane rural roads. A model for using regression analysis to predict crashes is presented. Exposure, curve length (CL), and difference in 85th-percentile speeds (ΔV85) between successive tangents and horizontal curves, as well as between successive curves, are used. The model's coefficients were different from the ones obtained for U.S. highways, although the values of the goodness-of-fit criteria were similar. In addition, the relationship between crashes and different speeds is analyzed, taking the difference in speed as a speed differential not exceeded by 85% of the drivers traveling under free-flow conditions (Δ85V), instead of considering it as ΔV85. The two models (ΔV85 versus Δ85V) give very similar results. Language: en

Review of Fundamentals of Road Design by Wolfgang KühnWIT Press, Billerica, MA; 2013; ISBN 978-1-84564-097-2; 327 pp.; $312.

Review of <i>Fundamentals of Road Design</i> by Wolfgang KühnWIT Press, Billerica, MA; 2013; ISBN 978-1-84564-097-2; 327 pp.; $312.

Application of global positioning system and questionnaires data for the study of driver behaviour on two‐lane rural roads

Methodologies based on naturalistic observation provide the most accurate data for studying drivers' behaviour. This study presents a new methodology to obtain naturalistic data related to drivers' behaviour in a road segment. It is based on the combination of using global positioning system data and drivers' questionnaires. The continuous speed profiles along a road segment and the characteristics of drivers, of their trips and the type of their vehicles can be obtained for a great amount of drivers. It has already been successfully used for several studies, such as the development of models to estimate operating speed profile in two-lane rural road segments; or the characterisation of driving styles. These operating speed models have been the key for the development of a new geometric design consistency model, allowing an easier road safety evaluation. Besides, knowledge on the human factors that influence speed choice may be useful for road safety media campaigns and education programs designers, and also for the improvement of intelligent driver assistance systems.

Application of Elman Neural Networks to Predict Truck’s Operating Speed

Prediction of vehicular operating speed is critical to evaluate the design consistency of road alignment. Elman neural networks are proposed to predict the truck’s 85th percentile operating speed. A total of 190 samples are collected from the two-lane rural roads and two factors are considered as input variables to the model including the curve radius and longitudinal slope. 100 samples are applied for training the networks to get the prediction model and the other 90 samples are used for the model validation. Additionally, the Elman neural networks are compared with back-propagation neural networks and linear regression, and the results show that the Elman neural networks are prior to the other two approaches and can be regarded as an alternative to predict truck’s operating speed.

국내 2+1차로 도로의 적정 교통량 및 계획기준 개발

현재 지방부 도로의 50% 이상을 차지하고 있는 양방향 2차로 도로는 4차로 도로로 확장하기에는 장래 교통량이 부족하지만 양방향 2차로 도로로 계속 운영하기에는 교통량이 많은 문제점이 발생되고 있는 경우가 많다. 또한 양방향 2차로도로의 추월행태에 따른 교통사고 위험과 사고 심각도가 높은 문제 해결을 위하여 2+1차로 도로의 도입을 검토하게 되었는데, 유럽의 여러 국가에서는 양방향 2차로 도로를 2+1차로 도로로 신설 또는 확장함으로써 예산 투자 효율화와 안전성 향상의 효과를 거둔 사례가 있는 것으로 나타났다. 본 연구는 영국, 독일, 스웨덴, 아일랜드, 핀란드 등에서 운영하고 있는 2+1차로 도로 사례를 검토하고 이를 국내 양방향 2차로 도로 개선방안의 하나로 도입하기 위한 가능성을 모색하기 위하여 수행되었다. 본 연구를 통해 국내 도로에 2+1차로 도로를 도입하는 경우 적정 교통량 수준을 산출하고, 이를 이용하여 2+1차로 도로의 계획기준을 개발하였다. 2+1차로 도로가 감당할 수 있는 교통량 수준을 시뮬레이션 프로그램 VISSIM(5.0)을 이용하여 분석하였고, 이를 국내 양방향 2차로 도로의 도로환경 조건을 고려하여 보정한 결과 중차량 비율에 따라 7,300대/일에서 17,000대/일 정도로 분석되었다. 이는 독일 등 유럽의 2+1차로 도로에서 관측된 최대교통량에 비해 약간 작은 값이고, 아일랜드의 관측 최대교통량(17,250대/일)과 유사한 값이다. Two-lane roads that occupy more than a half of rural highways in Korea have operational problems such as traffic congestion problems due to relatively high traffic volume and safety problems due to overtaking risks in two-lane highways. To solve these problems, a 2+1 road pattern that enables to improve traffic safety and operational efficiency of two-lane highways has been applied in Europe. In this study, in-depth applicability of 2+1 roads to Korean rural highways was investigated based on review results of the successful experience of European 2+1 roads. Then, given the Korean two-lane highway conditions, the service traffic volumes for Korean 2+1 roads was estimated. The analysis results showed that 17,000 veh./day might be the maximum traffic volumes for Korean 2+1 roads.

Traffic safety impacts of irregular overtaking in left-turn lanes at road intersections outside built-up areas

Overtaking is a high risk maneuver for road users, still drivers often accept this risk, moreover they often commit irregular overtaking maneuvers. The paper gives some overview on traffic violations and irregular overtaking maneuvers. Left-turn lanes on major roads are usual elements of un-signalized at-grade junctions on two-lane roads outside urban areas. In several cases the left-turn lane, built for safety reasons, has the unintended negative effect, of becoming a dangerous spot. The paper analyses overtaking maneuvers at left-turn lanes on Hungarian roads. Site surveys were completed at typical sites outside built-up areas. Relationships between the frequency of irregular maneuvers, accident statistics, geometric parameters and traffic data are analyzed.

Determination the capacity of two-lane suburban roads with neural networks and effect of speed on level of service

Introduction This study aimed to determine the capacity of two-lane suburban roads and its effect on level of service.

Field Evaluation of Automated Flagger Assistance Devices in Work Zones on Two-Lane Roads

Automated flagger assistance devices (AFADs) are designed to be operated remotely by a flagger positioned outside of the travel lanes and thus to reduce the flagger's exposure to vehicular traffic. There are two types of AFADs. One type uses a remote-controlled stop and slow sign to alternate the right-of-way; the other uses remote-controlled red and yellow lenses to alternate the right-of-way. A gate arm is required only with the latter. Although AFADs may have increased the safety of flaggers, there were concerns that motorists may have misunderstood AFADs and proceeded before it had been safe to do so. As part of a recent Texas Department of Transportation project, Texas A&amp;M Transportation Institute researchers conducted field studies at lane closures on two-lane, two-way roadways in Texas to assess the operational and safety effectiveness of AFADs relative to the use of flaggers. The research findings show that the violation rate for the stop–slow AFAD without a gate arm is the highest and is significantly higher than the violation rate for the red–yellow lens AFAD (which requires a gate arm). Adding a gate arm to the stop–slow AFAD decreased the violation rate such that it was not significantly different from the red–yellow lens AFAD. In addition, alternative supplemental signs increased motorists' understanding that the stop sign would have changed to a slow sign when motorists were allowed to proceed. Overall, the research findings show that some motorists violate AFADs, especially when the queue of vehicles going in the same direction is visible to the stopped motorist.

Evaluation of Safety Performance of Passing Relief Lanes

This paper documents the evaluation of the safety performance of passing relief lanes. A passing relief lane is an intermittently spaced additional lane on a two-lane road that provides drivers the opportunity to pass without having to cross into opposing traffic. The operational benefits are well known, but there is limited substantive evidence on the safety of these lanes. The study was based on data from Michigan, specifically traffic volume and crash history data for seven sites at which passing lanes were implemented within the study period, and for 100 reference sites (without passing lanes) and 231 passing lanes sites that existed throughout the study period. The analysis involved an empirical Bayes before–after evaluation and a comparative, cross-sectional evaluation of safety performance of locations with and without passing lanes. The methodologies were also applied to adjacent nontreated sites 1 mi upstream and downstream of the passing relief lane segment to examine possible spillover effects. From the results, crash modification factors (CMFs) were established for passing lanes in Michigan. These CMFs, which indicated significant safety benefits from passing relief lanes, may be considered for use in locations in other jurisdictions. The results from the cross-sectional and before–after evaluations were generally consistent.

Characterization of Opposite-Direction Road Departure Crashes in the United States

Opposite-direction crashes can be extremely severe because opposing vehicles often have high relative speeds. The objective of this study was to characterize the overall frequency of opposite-direction crashes as well as the frequency of crashes involving fatalities and serious injuries. The results of the study will guide future research and investment in infrastructure-based countermeasures to opposite-direction crashes, such as centerline rumble strips. The study used data from the National Automotive Sampling System (NASS) General Estimates System for 2010, the NASS Crashworthiness Data System for 2006 to 2010, and the Fatality Analysis Reporting System for 2010. The most common opposite-direction crash scenario was a driver departing the road driving over the centerline or the road edge to the left, which accounted for only 5% of nonjunction vehicle-to-vehicle crashes but 44% of serious injury and 49% of fatal crashes of the same type. Of the cross-over-to-left crashes, 72% of fatal crashes occurred on rural, undivided, two-lane roads and accounted for 1,659 fatal crashes in 2010. In cross-over-to-left crashes on rural two-lane roads, the driver was going straight or negotiating a curve in 88% to 94% of the crashes. The driver was overtaking another vehicle in only 2% of serious injury crashes and 6% of fatal crashes. Cross-over-to-left crashes on curves were to the outside of the curve more often than to the inside of the curve. This research suggests that countermeasures to opposite-direction crashes should focus on rural two-lane roads.

New Consistency Index Based on Inertial Operating Speed

The occurrence of road crashes depends on several factors, with design consistency (i.e., conformance of highway geometry to drivers' expectations) being one of the most important. A new consistency model for evaluating the performance of tangent-to-curve transitions on two-lane rural roads was developed. This model was based on the inertial consistency index (ICI) defined for each transition. The ICI was calculated at the beginning point of the curve as the difference between the average operating speed on the previous 1-km road segment (inertial operating speed) and the actual operating speed at this point. For the calibration of the ICI and its thresholds, 88 road segments, which included 1,686 tangent-to-curve transitions, were studied. The relationship between those results and the crash rate associated with each transition was analyzed. The results showed that the higher the ICI was, the higher the crash rate; thus, the probability of accidents increased. Similar results were obtained from the study of the relationship between the ICI and the weighted average crash rate of the corresponding group of transitions. A graphical and statistical analysis established that road consistency might be considered good when the ICI was lower than 10 km/h, poor when the ICI was higher than 20 km/h, and fair otherwise. A validation process that considered 20 road segments was performed. The ICI values obtained were highly correlated to the number of crashes that had occurred at the analyzed transitions. Thus, the ICI and its consistency thresholds resulted in a new approach for evaluation of consistency.

Daytime and Nighttime Passing Maneuvers on a Two-Lane Rural Road in Spain

Passing is one of the most complex driving maneuvers performed on two-lane rural roads and has important effects on road safety and traffic operation. Passing is affected by driving behavior, road geometry, traffic volume, and traffic composition as well as external factors. Research was developed to compare the passing process under daytime and nighttime conditions. An experimental method was designed to collect video data of passing maneuvers on a two-lane rural road segment located near Valencia, Spain. Two methods were used: (a) external observations of four passing zones with six video cameras and (b) an instrumented vehicle equipped with video cameras and laser rangefinders, driven slightly below the operating speed along a segment of the same road so it would be passed by other vehicles. A total of 291 maneuvers were observed, up to 20% of which were at night. Macroscopic analysis results indicated that approximately 17% of passes were at night, even though passing frequency and passing demand decreased at night. Also, the behaviors of individual drivers who passed other vehicles were different at night and during the day. Maneuvers limited by the presence of an opposing vehicle were performed more quickly at night, even if the accepted gaps were longer. In this case, a more difficult perception of distances to opposing vehicles and of vehicle speeds explained the differences. In contrast, maneuvers limited by sight distance (without a visible opposing vehicle) were slower at night. This observation matched a traditional hypothesis: passing at night is safer because the headlights of an opposing vehicle allow a driver to anticipate the vehicle's position before it becomes visible.

Some Limitations of the Models in the Highway Safety Manual to Predict Run-off-Road Crashes

Crash-prediction models in the current edition of the Highway Safety Manual (HSM) have been developed to predict crash frequency by collision type and severity level for specific types of roadways and sites. Each model is made up of three major components: safety performance functions (SPFs), crash modification factors, and calibration factors. The objective of this study was to identify the limitations of the prediction models in estimating single-vehicle, run-off-road (SVROR) crashes for roadside safety analyses and suggest needed changes and developments. The paper presents a review of the state of the models in HSM and focuses on SPFs. Data from FHWA's safety effects of cross-section design for two-lane roads database were used to gain insight about the characteristics of SVROR crashes and total crashes, and to identify the limitations of the current models in predicting the frequency, type, and severity of SVROR crashes. Three major areas of limitations of SPFs are discussed: (a) assumptions involved in development, (b) variables that are potentially important to roadside design but not considered, and (c) statistical bias and uncertainty of the model equations.

New geometric design consistency model based on operating speed profiles for road safety evaluation

To assist in the on-going effort to reduce road fatalities as much as possible, this paper presents a new methodology to evaluate road safety in both the design and redesign stages of two-lane rural highways. This methodology is based on the analysis of road geometric design consistency, a value which will be a surrogate measure of the safety level of the two-lane rural road segment. The consistency model presented in this paper is based on the consideration of continuous operating speed profiles. The models used for their construction were obtained by using an innovative GPS-data collection method that is based on continuous operating speed profiles recorded from individual drivers. This new methodology allowed the researchers to observe the actual behavior of drivers and to develop more accurate operating speed models than was previously possible with spot-speed data collection, thereby enabling a more accurate approximation to the real phenomenon and thus a better consistency measurement.Operating speed profiles were built for 33 Spanish two-lane rural road segments, and several consistency measurements based on the global and local operating speed were checked. The final consistency model takes into account not only the global dispersion of the operating speed, but also some indexes that consider both local speed decelerations and speeds over posted speeds as well.For the development of the consistency model, the crash frequency for each study site was considered, which allowed estimating the number of crashes on a road segment by means of the calculation of its geometric design consistency. Consequently, the presented consistency evaluation method is a promising innovative tool that can be used as a surrogate measure to estimate the safety of a road segment.

Squirrel gliders use roadside glide poles to cross a road gap

Tall wooden poles placed along roadsides may enable road crossing by gliding mammals. We investigated the use of 12-m-high roadside glide poles at one location in Brisbane. Camera traps on roadside poles detected squirrel gliders (Petaurus norfolcensis) on one or both poles on 60 of 310 operational nights including at least 16 confirmed crossings during 125 nights when both roadside cameras operated concurrently. This provides definitive evidence that squirrel gliders will readily use tall wooden poles to make glide-crossings of two-lane roads. This is consistent with other investigations of glide poles and suggests that poles should be installed more broadly to reconnect habitat for gliding mammals.

Quantifying the effect of present, past and oncoming alignment on the operating speeds of a two-lane rural road

In the last decades several studies were conducted in order to develop operating speed prediction models for two-lane rural roads. Many factors were found to affect the operating speed, such as radius of horizontal curve or curvature changes rate, grade, length of horizontal curve, deflection angle, sight distance, superelevation rate, side friction factor, and pavement conditions. Though this, many issues arise when there is an appreciable and continuous variance of geometric features along the road and, for example, short and long tangents coexist in the same road. In such conditions, assessing homogeneous sections, calibrating robust algorithms aimed at V85 prediction is a severe task and safety goals are not easily achieved. In the light of the abovementioned facts, objective and scopes of this work were confined into the quantifications of the effect of past, present, and future geometric elements on operating speeds. In particular, attention was focused on the consistency of the assumption of an environmental speed as a reference value for both short (dependent) and long (independent) tangents. Authors proposed a new operating speed model in which the geometric features of the previous and oncoming alignment were explicitly considered. The proposed speed prediction algorithm was validated on the basis of a wide experimental survey carried out in a rural road of the Province of Reggio Calabria – southern Italy. Problem modelling, experimental plan and results discussion are reported. Results proved the validity of the proposed model even if further experiments are needed to make the model able to predict the operating speed in different type of roads.