Two-lane Rural Roads Research Articles

Prediction of the Operating Speed Profile Approaching and Departing Intersections

The operating speed profile is a useful tool for diagnosing potential safety issues on existing highways and for alignment design. Unfortunately, existing operating speed profile prediction models do not take into account the presence of intersections along roads because a procedure to estimate a reliable operating speed profile on the road section along which driver speed behavior is affected by an intersection is not currently available. To overcome this limitation, driver speed behavior approaching and departing from at-grade intersections and modern roundabouts was studied and a procedure to predict the operating speed profile along a road section characterized by the presence of an intersection was developed. This simple procedure uses the same construction rules as the existing operating speed profile models in order to be easily integrated into them. The procedure developed predicts a reliable profile in the proximity of at-grade intersections and roundabouts along two-lane rural roads, thereby improving significantly the possibility of applying this useful tool to safety evaluations.

European Speed Environment Model for Highway Design-Consistency

The European road network is very large, and much of it is made up of two-lane rural roads. In Italy the road network requires adjustment work to improve mobility safety management. One of the most important tools for this analysis is the operating speed (V85) profile. In many design standards, different formulations are used for estimating V85, obtained on the basis of research carried out at different times and in different contexts. The aim of the research presented in this study is to analyze driver speed behavior on two-lane rural highways. The study was conducted using traffic counters, able to record in both directions and for every passage of a vehicle, its length, instant speed and direction. The survey plan was elaborated to satisfy different research objectives. The readings were taken by keeping every section under observation for 3, 6 or 12 hours. The data were collected on 11 homogeneous sections of highway. The database consisted of free-flow passenger car speeds and various geometric data from 103 sites. Data were collected at sites to both develop and validate equations. The proposed model includes the radius of horizontal curvature and the “Speed Environment”, which is defined as the speed at which users travel in free-flow conditions when they are not constrained by the alignment of the highway.

Driver perception of roadside configurations on two-lane rural roads: Effects on speed and lateral placement

This paper reports the results of a driving simulator study which sought to analyze the effect that: (a) three roadside configurations on a two-lane rural road lined with trees have on speed and lateral position of the driver, depending on different cross-sections as well as geometric elements; (b) the beginning of the guardrail barrier has upon the driver's behavior whenever this occurs on the left curve, right curve or tangent.A two-lane rural road lined with trees was designed and implemented in an advanced-interactive driving simulator. Two different cross-sections (with and without a shoulder), which were combined with three roadside configurations (only trees, trees and barriers, trees and barriers having undergone a treatment), were tested. Six road scenarios were then analyzed. Thirty-six drivers (33 were deemed to be valid and used for the analysis) drove in the simulator using these scenarios and the speed and lateral placement values were collected.Statistical analysis showed that the driver behavior was only affected by the cross-sections and geometric elements but not by roadside configurations. Although the presence of trees along the road represents a factor that increases the severity of run-off-road accidents, drivers do not change their behavior when barriers are not present.Concerning the effects of the beginning of the barrier, MANOVA revealed a main effect for roadside configuration on lateral position but not on speed. There was also a clear tendency of drivers to “cut” both the right curves as well as the left curves in order to minimize the speed reduction in the tangent–curve–tangent transition. These main results allow useful suggestions to be made as regards safety measures for improving road safety on two-lane rural roads lined with trees.

Effect of Horizontal Alignment Characteristics on Capacity Loss at Rural Two-Lane Roads

Effect of Horizontal Alignment Characteristics on Capacity Loss at Rural Two-Lane Roads

Effects of reduced threshold of automated speed enforcement on speed and safety

This study was designed to evaluate the effects of a reduced threshold of the fixed automated speed enforcement system on speed and safety on a two-lane rural road. The threshold was lowered from 20 km/h to 4 km/h and the public was informed about the change. Driving speeds on the experimental and control road before and after the change were compared. The main results showed that the reduced threshold decreased the mean speed by 2.5 km/h, the standard deviation of speed by 1.1 km/h and the proportion of exceeding vehicles by 11.8 percentage units. In conclusion, lowering the threshold of automated speed enforcement combined with an appropriate information campaign bring about a significant speed reduction that could contribute to substantial safety benefits. Language: en

New Approach to Defining Continuous Speed Profile Models for Two-Lane Rural Roads

Despite a large body of research on operating speeds, there is still much to learn about the factors that affect free-flow speeds, especially with regard to the development of a continuous speed profile for two-lane rural highways. This paper presents a new approach to modeling driver speed profile along two-lane rural roads. Speed data regarding individual drivers traveling on selected two-lane rural roads were sampled during a naturalistic experiment that used an onboard Global Positioning System (GPS). GPS devices facilitate the collecting and processing of continuous speed data. Unlike spot speed measurements, which have typically been collected in similar studies, continuous speed data are useful for studying the actual speed profile with regard to acceleration–deceleration behavior and maximum speed on tangents and curves. New variables are used in the regression equation. These variables refer to the horizontal curvature and the vertical grade as weighted values of the geometric features of the alignment preceding and following the vehicle position. To predict the operating speed, the model takes into account the geometric alignment of the road preceding and following the vehicle, as this information is used by drivers to establish the driving task, which is based on memory expectation, vehicle dynamics, and visual perception. The final result is an algorithm for modeling a continuous speed profile without previous assumption of acceleration–deceleration rate and constant speed on tangents and curves.

Effect of Roadside Features on Single-Vehicle Roadway Departure Crashes on Rural Two-Lane Roads

One of the most important tasks in traffic safety is investigating the relationship between motor vehicle crashes and the geometric characteristics of roadways. A large body of previous work provides meaningful results on the impact of geometric design on crash frequency. However, little attention has been paid to the relationship between roadway departure crashes and relevant roadside features such as lateral clearance, side slope condition, and driveway density. The lack of roadside data for use in estimating rigorous statistical models has been a major obstacle to roadside safety research for many years. This study investigated the relationship between single-vehicle roadway departure crashes and roadside features. Two types of models were developed: a negative binomial model of crash frequency and a multinomial logit model of crash severity. The study used field data collected in four districts in Texas. The results showed that shoulder width, lateral clearance, and side slope condition had a significant effect on roadway departure crashes. Crash frequency and severity increased when lateral clearance or shoulder width decreased and when the side slope condition became worse. Driveway density was not found to have a significant influence on crash frequency or severity.

Calibration of Highway Safety Manual Safety Performance Function

This paper documents the calibration of the Highway Safety Manual (HSM) safety performance function (SPF) for rural two-lane two-way roadway segments in Utah and the development of new SPFs through negative binomial regression. Crash data from 2005 to 2007 on 157 selected study segments in Utah provided a 3-year frequency of observed crashes to calibrate the HSM SPF and develop new models. The calibration factor for the HSM SPF for rural two-lane two-way roads in Utah is 1.16, indicating that the original HSM model under predicts crashes in Utah. The HSM suggests that jurisdiction-specific SPFs may predict crashes with greater reliability than calibrated SPFs. The following variables were significant in each of the four models developed by this research: annual average daily traffic (AADT), segment length, speed limit, and the percentage of AADT composed of multiple-unit trucks. AADT and segment length are used in the HSM SPF; speed limit and the percentage of AADT composed of multiple-unit trucks were found to correlate significantly with observed crash frequencies. The fourth negative binomial model developed in the study would be the best SPF to predict crashes on rural highways in Utah. As encouraged by the HSM and contemporary research, the empirical Bayes method can be applied with each jurisdiction-specific SPF because the analysis provided an overdispersion parameter for each model.

Safety Performance Functions for Low-Volume Roads

This paper analyzes roadway safety conditions using the network approach for a number of Italian roadways within the Province of Salerno. These roadways are characterized by low-volume conditions with a traffic flow of under 1000 vpd and they are situated partly on flat/rolling terrain covering 231.98 km and partly on mountainous terrain for 751.60 km. Since 2003, the Department of Transportation Engineering at the University of Naples has been conducting a large-scale research program based on crash data collected in Southern Italy. The research study presented here has been used to calibrate crash prediction models (CPMs) per kilometer per year. The coefficients of the CPMs are estimated using a non-linear multi-variable regression analysis utilizing the least – square method. In conclusion, two injurious crash prediction models were performed for two-lane rural roads located on flat/rolling area with a vertical grade of less than 6% and on mountainous terrain with a vertical grade of more than 6%. A residuals analysis was subsequently developed to assess the adjusted coefficient of determination and p-value for each assessable coefficient of the prediction model. CPMs are a useful tool for estimating the expected number of crashes occurring within the roads’ geometric components (intersections and road sections) as a function of infrastructural, environmental, and roadway features. Several procedures exist in the scientific literature to predict the number of crashes per kilometer per year. CPMs can also be used as a tool for safety improvement project prioritization.

Identifying Significant Predictors of Head-on Conflicts on Two-Lane Rural Roads Using Inductive Loop Detectors Data

Objective: To identify the significant factors that influence head-on conflicts resulting from dangerous overtaking maneuvers on 2-lane rural roads in Iran. Methods: A traffic conflict technique was applied to 12 two-lane rural roads in order to investigate the potential situations for accidents to occur and thus to identify the geometric and traffic factors affecting traffic conflicts. Traffic data were collected via the inductive loop detectors installed on these roads, and geometric characteristics were obtained through field observations. Two groups of data were then analyzed independently by Pearson's chi-square test to evaluate their relationship to traffic conflicts. The independent variables were percentage of time spent following (PTSF), percentage of heavy vehicles, directional distribution of traffic (DDT), mean speed, speed standard deviation, section type, road width, longitudinal slope, holiday or workday, and lighting condition. Results: It was indicated that increasing the PTSF, decreasing the percentage of heavy vehicles, increasing the mean speed (up to 75 km/h), increasing DDT in the range of 0 to 60 percent, and decreasing the standard deviation of speed significantly increased the occurrence of traffic conflicts. It was also revealed that traffic conflicts occur more frequently on curve sections and on workdays. The variables road width, slope, and lighting condition were found to have a minor effect on conflict occurrence. Conclusion: To reduce the number of head-on conflicts on the aforementioned roads, some remedial measures are suggested, such as not constructing long “No Passing” zones and constructing passing lanes where necessary; keeping road width at the standard value; constructing roads with horizontal curves and a high radius and using appropriate road markings and overtaking-forbidden signs where it is impossible to modify the radius; providing enough light and installing caution signs/devices on the roads; and intensifying police control and supervision on workdays, especially in peak hours.

Evaluation of performance measures for rural two-lane roads in Egypt

This paper presents an empirical evaluation of the relationship between operational performance and platooning phenomenon in rural two-lane roads in Egypt. Seven performance measures and three platooning variables were defined and calculated for eight study sites using traffic data from roads in Minoufiya governorate, Egypt. Using graphical and statistical analyses, the associations between the performance measures and the platooning variables were examined. The results showed that the follower density performance measure was found to have the strongest correlations to platooning variables. Among the platooning variables investigated, traffic flow in the direction of travel has the highest correlations with performance measures. The study demonstrated that the relationship between follower density and traffic flow is better described by a quadratic form. Finally, threshold values for different levels-of-service were proposed. This might help traffic engineers, in Egypt, to evaluate operational performance using criteria that reflect the local conditions of the area under study.

Efficacies of roadway safety improvements across functional subclasses of rural two-lane highways

Introduction Highway crash occurrence is a leading cause of unnatural deaths, and highway agencies continually seek to identify engineering measures to reduce crashes and to assess the efficacy of such measures. Most past studies on the effectiveness of roadway improvements in terms of crash reduction considered all rural two-lane sections as a single category of roads. However, it may be hypothesized that the differences in the mobility and accessibility characteristics that are reflected in (and due to) the different design standards between different functional subclasses in the rural two-lane highway system can lead to differences in efficacies of safety improvements at these subclasses. This paper investigates the efficacy of roadway improvements, in terms of crash reduction, at the various subclasses of rural two-lane highways. Methods An empirical analysis of safety performance at each of the three subclasses of rural two-lane highways was carried out using the negative binomial modeling technique. For each subclass, crash prediction models were developed separately for the three levels of crash severity: property-damage only, injury, and fatal/injury. The crash factors that were considered include lane width, shoulder width, pavement surface friction, pavement condition, and horizontal and vertical alignments. After having developed the safety performance functions, the effectiveness (in terms of the extent of crash reduction, for different levels of crash severity) of highway safety enhancements at each highway subclass were determined using the theoretical concepts established in past literature. These enhancements include widening lanes, widening shoulders, enhancing pavement surface friction, and improving the vertical or horizontal alignment. Results and Conclusion The study found that there is empirical evidence to justify the decomposition of the family of rural two-lane roads into its constituent subclasses for purposes of analyzing the effectiveness of safety enhancement projects and thus to avoid underestimation or overestimation of benefits of safety improvements at this class of highways.

A study on crashes related to visibility obstruction due to fog and smoke

Research on weather effects has focused on snow- or rain-related crashes. However, there is a lack of understanding of crashes that occur during fog or smoke (FS). This study presents a comprehensive examination of FS-related crashes using crash data from Florida between 2003 and 2007. A two-stage research strategy was implemented (1) to examine FS-related crash characteristics with respect to temporal distribution, influential factors and crash types and (2) to estimate the effects of various factors on injury severity given that a FS-related crash has occurred. The morning hours from December to February are the prevalent times for FS-related crashes. Compared to crashes under clear-visibility conditions, FS-related crashes tend to result in more severe injuries and involve more vehicles. Head-on and rear-end crashes are the two most common crash types in terms of crash risk and severity. These crashes were more prevalent on high-speed roads, undivided roads, roads with no sidewalks and two-lane rural roads. Moreover, FS-related crashes were more likely to occur at night without street lighting, leading to more severe injuries.

Analysis of speed characteristics for rural two-lane roads: A field study from Minoufiya Governorate, Egypt

This paper presents an analysis into speed characteristics on rural two-lane highways under existing conditions. Empirical data from several study sites on intercity rural two-lane roads in Minoufiya Governorate, Egypt were used in this investigation. Three separate however relevant analyses are presented in this paper. The first analysis investigates the relationship between 85th percentile speed and headway to define a headway value corresponding to free moving vehicles. The second analysis examines the suitability of the posted speed limits on the roads under study. The third and last analysis inspects the conformity of the study sites’ speed data with normal distributions. It was found that the 85th percentile speed took a constant value at headway equal to 5 s or more. Also, a significant proportion of drivers exceed the posted speed limit as well as the current speed limit may not be appropriate. Finally spot speed data follow a normal distribution.

Performance of Safety Indicators in Identification of Black Spots on Two-Lane Rural Roads

Defining a black spot is not as perceptual as it may appear. Unusually high crash counts do not necessarily indicate a real safety problem. When black spots on two-lane rural roads with low and medium traffic volumes are being identified, a reduced number of observed crashes is a critical issue that can emphasize weak results obtained with various safety indicators and checks. It is generally assumed that an empirical Bayesian (EB) estimate represents the best approach for the identification of black spots, but it is difficult to define quantitatively the precision of estimates that are arrived at with different procedures. Because traffic volume, segment length, and crash observation period are critical issues in the identification of black spots and can emphasize the quality of the results obtained with safety indicators and checks, definition is needed of the limits and errors that can be expected when inadequate indicators and procedures are used to identify black spots on two-lane rural roads. A Monte Carlo simulation was used to produce theoretical crash data similar to empirical data, and the data were used to define a priori hazardous sites and, therefore, to assess whether a method could correctly identify such sites. The accuracy and efficiency of procedures are compared on the basis of observed frequency of crashes, crash rate, EB estimation, and the potential for safety improvement (PSI). As a general rule, even if some arrangements can mitigate the lower performance of some indicators, the best practice is to use the indicators based on the EB estimation PSI to identify true positives.

Estimation of Safety Effectiveness of Widening Shoulders and Adding Passing Lanes on Rural Two-Lane Roads

There is a need to evaluate the costs and benefits of potential safety improvements so that limited budgets for low-volume roads may be used most effectively. Increasing the width of shoulders and adding passing lanes have been regarded as economical and effective safety improvements. The state of Kansas has more than 2,000 mi (3,219 km) of highway that may need these improvements, most of which are rural two-lane roads. This study considered how historical data and crash modification factors (CMFs) were combined to estimate the safety benefits of widening shoulders and adding passing lanes on rural two-lane roads. The objective was to determine specific CMFs for the state of Kansas and states with similar rural environments as well as to estimate the number of crashes avoided. Safety and traffic volume data for rural two-lane roads from 2000 to 2008 were obtained from the State of Kansas and combined with existing models from earlier studies to create state-specific CMFs to more accurately estimate safety benefits. It was determined in this study that CMFs for shoulder widening and the addition of passing lanes for low-volume roads are 0.95 and 0.65, respectively. These CMFs are based on shoulder widening from 2 ft (0.61 m) to 8 ft (2.44 m) or construction of a short four-lane passing section. From these results, 20-year projections were developed for the benefits in crash reductions that could be achieved through implementing these safety improvements.

Models of Operating Speeds for Low-Volume Roads

Recent studies have documented a noticeable disparity between the speeds for which roads are designed and the actual operating speeds. An important reason for driving errors on two-lane rural roads is the misjudgment of the real course of the road by road users. Unfavorable visibility conditions are one of the problems of road infrastructure that can be detected on existing low-volume roads. Therefore an operating speed model was developed to calculate the contribution made by sight distance, and to be a useful tool for planners in the study of the safety of existing roads. Seven low-volume roads in the province of Salerno, Italy, were studied. The study identified operating speeds on 84 curves; the relative sight distance, radius, radius of the previous curve, length of the tangent before the curve, curvature change rate, development of the curve, and number of speed changes made during the study were determined for each curve. Because of the different characteristics of the roads analyzed, once the data were collected it was possible to develop two operative speed models. The first was suitable for roads characterized by consecutive curves alternating with small tangents and the second model was mainly intended for roads characterized by a small number of curves that were preceded and followed by long tangents.

A Collision Warning System for rear-end collision: a driving simulator study

Collision warning and collision avoidance systems are emerging automotive safety technologies that assist drivers in avoiding rear-end collisions. Their function is to allow the driver enough time to avoid the crash and yet avoid annoying the driver with alerts perceived as occurring too early or unnecessary. The aim of this paper was analyzing the driver's behavior in order to define effective driver assistance systems which can be readily accepted by the driver. A study was performed with an interactive fixed-base driving simulator. A sample of 32 drivers drove on a two-lane rural road. Four different driving traffic conditions were implemented. The data recorded during the tests were analyzed to assess the safety distances required by the driver during a car-following situation. Based on the risk perception of the driver a new collision warning algorithm was developed.

Evaluation of Safety Identification Methods for Low-Volume Roads Using Monte Carlo Simulation

Two-lane rural roads characterized by low traffic volume (fewer than 3,000 vehicles per day) represent a specific road typology of interest in safety analysis. Correct identification of black spots (sites in which the expected number of crashes is abnormally high) is crucial for the road administration when the location and ranking of improvements are chosen. Simply observing unusually high crash counts does not necessarily indicate a true safety problem. In black spot identification on two-lane rural roads with low traffic volume, the reduced number of observed crashes is a critical issue that can emphasize weak results carried out with different safety indicators and control checks. Generally it is assumed that the empirical Bayesian estimate represents the best approach for black spot identification, but the precision of the estimation among different procedures is difficult to define quantitatively. The simulation approach is able to identify crash data similar to empirical data with the unique possibility to define a priori hazardous sites and therefore assess whether a method can correctly identify them. The Monte Carlo simulation presented here was able to define the accuracy and efficiency of the procedures on the basis of observed frequency of crashes, crash rate, empirical Bayes estimation, and potential for safety improvement. The results show that an appropriate selection of exposure values can mitigate the lower performance of some indicators, but the best practice is to use the empirical Bayes approach to identify true positives.

Methodology for Checking Shortcomings in Three-Dimensional Alignment

Road design by highway planning authorities and planning offices is performed at three separate levels: the horizontal and the vertical projections and the cross section. Experiments have shown that shortcomings in the three-dimensional (3-D) alignment may still occur when these three levels are processed separately and then superimposed. It makes sense to calculate virtual perspective views and special control parameters with the use of visualization tools and then to check the 3-D alignment with those tools. Shortcomings of this kind can cause accidents, particularly on two-lane rural roads. Unified model assumptions that match the driver's vision must be set to ensure the comparability of the central perspective views. Drivers absorb images from a central perspective when driving along a road. A driver's inability to recognize a section of the road in the driving area ahead gives rise to blind sections. Designers need to use standard 3-D elements as much possible. These shortcomings are of two major types: those that are safety related and those that are merely aesthetic. A methodology has been developed to check the 3-D alignment for shortcomings in the three basic stages (checking for standard 3-D elements, safety-related shortcomings, and aesthetic shortcomings). By using the visualization tool VISS ALL 3D, the design engineer can calculate the virtual perspective views with the safety-related shortcomings and illustrate them in the blind-section graph. Shortcomings in the 3-D alignment must be eliminated at the end of the redesign process.