Rural Multilane Highways Research Articles

Improving Simulation Models of Unsignalized Intersections on Rural Multilane Highways through Calibration Using Naturalistic Driving Study Data from Strategic Highway Research Program 2

The aim of this study is to create a calibration method for traffic simulation models of two crucial movements at unsignalized intersections on rural divided highways. This analysis draws on data from the Naturalistic Driving Study, specifically direct left turn (DLT) movements at conventional intersections and right turn followed by U-turn (RTUT) movements at restricted crossing U-turn (RCUT) intersections. Using 453 naturalistic trips from 79 drivers, the speed trajectory, stopping behavior, lane utilization, and acceleration and deceleration rates were analyzed. Three-step and four-step calibration methods were then developed for the Vissim simulation models for DLT and RTUT movements, respectively, which were verified by comparison with naturalistic driving data. The calibrated Vissim models were verified by comparing the naturalistic driving speed trajectories of DLT and RTUT movements. The results show that calibrated models can improve the operational analysis for overall unsignalized intersections on rural multilane divided highways.

Assessing the Performance of Highway Safety Manual (HSM) Predictive Models for Brazilian Multilane Highways

This paper assesses the performance of Highway Safety Manual (HSM) predictive models when applied to Brazilian highways. The study evaluates five rural multilane highways and calculates calibration factors (Cx) of 2.62 for all types of crashes and 2.35 for Fatal or Injury (FI) crashes. The Goodness of Fit measures show that models for all types of crashes perform better than FI crashes. Additionally, the paper assesses the application of the calibrated prediction model to the atypical year of 2020, in which the COVID-19 pandemic altered traffic patterns worldwide. The HSM method was applied to 2020 using the Cx obtained from the four previous years. Results show that for 2020, the observed counts were about 10% lower than the calibrated predictive model estimate of crash frequency for all types of crashes, while the calibrated prediction of FI crashes was very close to the observed counts. The findings of this study demonstrate the usefulness of HSM predictive models in identifying high-risk areas or situations and improving road safety, contributing to making investment decisions in infrastructure and road safety more sustainable.

Investigating speed-safety association: Considering the unobserved heterogeneity and human factors mediation effects.

The relationship between mean speed and crash likelihood is unclear in the literature. The contradictory findings can be attributed to the masking effects of the confounding variables in this association. Moreover, the unobserved heterogeneity has almost been criticized as a reason behind the current inconclusive results. This research provides an effort to develop a model that analyzes the mean speed-crash frequency relationship by crash severity and type. Also, the confounding and mediation effects of the environment, driver, and traffic-related attributes have been considered. To this end, the loop detector and crash data were aggregated daily for rural multilane highways of Tehran province, Iran, covering two years, 2020-2021. The partial least squares path modeling (PLS-PM) was employed for crash causal analysis along with the finite mixture partial least squares (FIMIX-PLS) segmentation to account for potential unobserved heterogeneity between observations. The mean speed was negatively and positively associated with the frequency of property damage-only (PDO) and severe accidents, respectively. Moreover, driver-related variables, including tailgating, distracted driving, and speeding, played key mediation roles in associating traffic and environmental factors with the crash risk. The higher the mean speed and the lower the traffic volume, the higher odds of distracted driving. Distracted driving was, in turn, associated with the higher vulnerable road users (VRU) accidents and single-vehicle accidents, triggering a higher frequency of severe accidents. Moreover, lower mean speed and higher traffic volume were positively correlated with the percentage of tailgating violations, which, in turn, predicted multi-vehicle accidents as the main predictor of PDO crash frequency. In conclusion, the mean speed effects on the crash risk are entirely different for each crash type through distinct crash mechanisms. Hence, the distinct distribution of crash types in different datasets might have led to current inconsistent results in the literature.

Modeling Operating Speed on Multilane Highways Using Global Positioning System Data

This study aims at developing models to predict the operating speeds of passenger cars on horizontal curves of rural multi-lane highways. A total of 16 compound curves and 35 simple curves located on two major rural multi-lane divided highways in Jordan were selected for the study. Continuous speed data were collected using an affordable (low cost) speedometer application loaded on smartphones equipped with Global Positioning System (GPS) technology. A stepwise multiple linear regression analysis at a 95% confidence interval has been performed to develop the speed prediction models. The obtained model at the beginning of the compound curve indicated that the 85th percentile speed at the midpoint of approach independent tangent and the deflection angle of the first curve is found to be statistically significant to predict operating speed. At both points of the compound curve and end of the curve, the significant variables were the radius of the first curve and the total length of the compound curve. For simple curves, the obtained models indicated that the curve radius and the 85th percentile speed at the midpoint of approach independent tangents were positively correlated with the operating speed at beginning of curve, while the degree of curvature was negatively correlated with the operating speed at both middle and end of the curve.

Predicting operating speed: comparison of linear regression and structural equation models

The aim of this research was to predict operating speed by considering geometric and roadside factors. Although most previous studies have employed linear regression modelling (LRM) to predict operating speed, this study recommends structural equation modelling (SEM) for the prediction of operating speed on rural multi-lane highways. In addition to geometric variables, LRM takes roadside variables into account. When employing SEM in this work, two latent variables were defined, namely ‘roadside effects’ and ‘geometric effects’. The first latent variable was the combination of land-use type, land-use density and number of accesses per segment, while the second was extracted from the segment length, highway grade, curvature, the presence of a guardrail and flat roadside slope, and the posted speed limits. The residual analysis and R2 values for LRM and SEM suggest that SEM demonstrates superior modelling performance compared with LRM. These results show the significant role of latent variables in predicting speed, which cannot be achieved through ordinary LRM.

Safety Performance Evaluation of the New Mega Elliptical Roundabout Interchanges Using the Surrogate Safety Assessment Model

Mega elliptical roundabouts are considered a new kind of intersection and can be found on rural multilane highways. Their form is that of an elongated ellipse. They combine the best advantages of an unconventional median U-turn intersection and roundabout. The purpose of this research is analyzing safety performance for mega elliptical roundabout interchange using the VISSIM software version 4.30 and the surrogate safety assessment model (SSAM) software version 3. This research also considered eight other interchange designs to compare them with the mega elliptical roundabout interchange. In total, 20 scenarios were analyzed using VISSIM version 4.30 then tested by SSAM software version 3. To compare the different interchanges in terms of the mean values of conflicts, the one-way analyses of variance (ANOVA) were conducted. Based on the research results, a mega elliptical roundabout interchange was one of the best interchanges studied in this research in relation to the frequency of conflicts as a total and the frequency of crossing conflicts.

Cross-Sectional Study of Vehicle Speeds on Rural Four-Lane Highway Curves

Research has consistently shown that horizontal curves are often associated with increased crash rates compared with similar tangent highway sections. These crashes are often related to speed and the difficulty of judging the severity of the curve. Curve speed models are used for a variety of applications, including assessing operational characteristics, evaluating design speed, conducting spot safety analyses, and setting curve advisory speeds. However, most of the documented curve speed models apply to rural two-lane highways, while relatively few models have been developed for rural multilane highways. These types of highways may exhibit different driver behavior in curves because of their more generous geometric design and higher traffic volumes. The objective of this paper is to document models that have been developed for several types of rural four-lane highways, including undivided highways, divided highways, and freeways. The authors developed models that account for geometric characteristics like curve radius, superelevation rate, and deflection angle, as well as operational characteristics like approach tangent (TN) speed. These models were calibrated using a database of about 46,000 vehicles across 29 horizontal curve sites in central Texas.

A Novel Methodology for Estimating the Capacity and Level of Service for the New Mega Elliptical Roundabout Intersection

Mega elliptical roundabout is a new intersection on rural multilane highways. This intersection was developed in a previous paper using simulation data, and the authors found that it is better than interchange (full cloverleaf) in most scenarios of traffic flow. Basically, there are no guidelines or procedures for designing mega elliptical roundabout in AASHTO Green Book, Federal Highway Administration guides, and Highway Capacity Manual. Thus, the purpose of this study is to analyze the traffic operation performance and propose a methodology for calculating the capacity of mega elliptical roundabout and also the level of service by gap acceptance theory. Moreover, this research studied the influence of different values of truck ratios and also different values of a major highway speed on geometric design and traffic operation performance for mega elliptical roundabout. To validate the thoroughness of the proposed methodology, VISSIM simulations were conducted. This research will assist practitioners in determining the appropriate geometric design, assessing mega elliptical roundabout intersections, and making comparisons with other alternatives.

Mega elliptical roundabouts versus grade-separation interchange

The mega elliptical roundabout is a new idea for intersections on rural multilane highways in the form of an elongated ellipse. Basically, there are no procedures or guidelines for designing the mega elliptical roundabout in the Highway Capacity Manual, Federal Highway Administration guides or the American Association of State Highway and Transportation Officials' ‘Green Book’. This research therefore presents the best geometric design scenarios of mega elliptical roundabout intersections at various traffic flows for all intersection entrances. The basis for selecting the best scenarios is to achieve minimum delay time, minimum emissions and minimum fuel consumption. This was studied at the intersection of a six-lane divided highway with a four-lane divided highway when the traffic enters from four approaches. Moreover, this research proposes the cases in which the mega elliptical roundabout is better than an interchange (full cloverleaf), and suggests the best time to make a decision to change from a mega elliptical roundabout to an interchange (full cloverleaf). The study was conducted by using Vissim software (version 10.00-02). In total, 1134 scenarios were analysed.

The Practical Effectiveness of Advanced Driver Assistance Systems at Different Roadway Facilities: System Limitation, Adoption, and Usage

This research proposes a method to estimate the practical effectiveness of 6 advanced driver assistance systems (ADAS) in avoiding crashes on different roadway facilities (locations). The systems include blind spot warning/lane change warning (BSW/LCW), forward collision warning (FCW), intersection movement assist (IMA), pedestrian crash avoidance and mitigation (PCAM), lane departure warning (LDW) and left turn assist (LTA) systems. The method involves the use of meta-analysis and quasi-induced exposure methodologies to estimate the distribution of effectiveness factors across the driver population. These factors include system operating conditions, system adoption rates and system usage features. Then a Monte-Carlo procedure is applied to sample these factors for simulating the practical ADAS effectiveness. The research shows that the practical effectiveness could be as much as 48.25% lower than the ideal effectiveness proposed by previous research. It is also found that BSW/FCW, PCAM, FCW and LDW systems exhibited the highest effectiveness when operating on urban expressways/freeways. On rural multilane highways, such systems are demonstrated to have the least effectiveness. Furthermore, LTA systems are found to perform better at rural intersections than at urban intersections while the conclusion is contrary regarding IMA systems. Among the six systems, BSW/LCW has the most consistent performance among facilities, while LTA is most likely to be affected by facility type. The integrated system of six ADAS systems could prevent at most 29.50% of total crashes on urban multi-lane highways, while its lowest practical effectiveness is 13.72% on rural two-lane highways. Finally, technical and policy implications of the results are discussed.

An Approach for Development of Local Safety Performance Functions for Multi-Lane Rural Divided Highways in Egypt

Egypt is a middle-income country, belonging to the Eastern Mediterranean Region (EMR). Egypt used to be the worst performing EMR country, with over 45 fatalities per 100,000 population. It is considered an example case of many EMR countries in the region where there is a need for quantitative assessment of safety on its roads. The Highway Safety Manual (HSM) offers several functions to calculate safety performance (SPFs), which can estimate crash frequency on a highway network according to its geometric and traffic characteristics. The HSM was developed in the United States using road and crash data specific to its environment. Jurisdictions and other non-U.S. regions were encouraged to develop locally derived models suitable for the local characteristics of roads and crashes. The objective of this paper is to assess the suitability of using the HSM models on rural multi-lane divided highways in Egypt. The calibrated SPFs considering Egyptian road factors were compared with the actual crash events. The results showed that there was a need to develop locally derived SFPs using negative binomial models. The modeling approach and a validation procedure were presented and are applicable when developing local SPFs to compare how well the model performs to the actual data, and to HSM calibrated models. The models were created using 90% of the data and tested on the remaining 10% of the data. The study found that the results relating to driver behavior would help designers in regions other than the United States to benefit from the HSM.

Evaluating the Relationship between Operating Speed and Collision Frequency of Rural Multilane Highways Based on Geometric and Roadside Features

Speed is one of the main functional factors that affect road safety in terms of both collision occurrence and collision severity. Previous studies have shown that several roadside and geometric features affect road safety and operating speed. This paper aims to evaluate the effects of roadside and geometric features on operating speed and collision frequency, simultaneously. For this purpose, the operating speed data of 103 segments along with their accident data and roadside and geometric characteristics were collected. Structural equation modelling (SEM) with latent variables was employed to model operating speed and collision frequency, simultaneously. Two latent variables including “geometric effect” and “roadside effect” were defined in SEM. The first latent variable is the combination of the natural logarithm of the segment length, longitudinal slope, the presence of a 2-meter paved shoulder, and curvature of the segment. The indicators of the second latent variable are the number of accesses and the presence of residential land use. The results show that the latent variable “roadside effect” increases collision frequency by a standard regression weight of 3.455; however, it reduces operating speed by a standard regression weight of –0.385. Also, the latent variable “geometric effect” causes an opposite effect on collision frequency and operating speed by the standard regression weight of –5.313 and 0.730, respectively. Besides, lower operating speed causes a reduction in the collision frequency by the standard regression weight of 7.734. The results of this study can be useful for designers and road safety agencies to improve road safety.

Finite mixture modeling approach for developing crash modification factors in highway safety analysis

This study aimed to investigate the relative performance of two models (negative binomial (NB) model and two-component finite mixture of negative binomial models (FMNB-2)) in terms of developing crash modification factors (CMFs). Crash data on rural multilane divided highways in California and Texas were modeled with the two models, and crash modification functions (CMFunctions) were derived. The resultant CMFunction estimated from the FMNB-2 model showed several good properties over that from the NB model. First, the safety effect of a covariate was better reflected by the CMFunction developed using the FMNB-2 model, since the model takes into account the differential responsiveness of crash frequency to the covariate. Second, the CMFunction derived from the FMNB-2 model is able to capture nonlinear relationships between covariate and safety. Finally, following the same concept as those for NB models, the combined CMFs of multiple treatments were estimated using the FMNB-2 model. The results indicated that they are not the simple multiplicative of single ones (i.e., their safety effects are not independent under FMNB-2 models). Adjustment Factors (AFs) were then developed. It is revealed that current Highway Safety Manual’s method could over- or under-estimate the combined CMFs under particular combination of covariates. Safety analysts are encouraged to consider using the FMNB-2 models for developing CMFs and AFs.

Is Horizontal Curvature a Significant Factor of Safety in Rural Multilane Highways?

The Highway Safety Manual (HSM) crash prediction models estimate the expected number of crashes for different facility types. Models in Part C of the first edition of the HSM include crash prediction models for divided and undivided rural multilane highway segments. Each of the HSM crash prediction models for highway segments is composed of a safety performance function (SPF) that is a function of annual average daily traffic and segment length plus a series of crash modification factors (CMFs). The SPF estimates the number of crashes for a site if the site features are of base condition. The effects of other features of the site, if their values are different from the base condition, are carried out through use of CMFs. Existing models for rural multilane segments do not have any CMFs for horizontal curvature. The goal of this research was to investigate whether horizontal alignment has any significant effect on crashes on these types of facilities and if so, to develop a CMF for this feature. Washington State cross-sectional data from the Highway Safety Information System Laboratory were used in this research. Data from 2007 to 2009 were used to conduct the investigation and 2010 and 2011 data were used to validate the results. As the results showed, horizontal curvature has a significant safety effect on rural multilane highways, and using a CMF for horizontal curvature improves the prediction of crashes significantly for tangent and curve segments.

Minimum sample sizes for estimating reliable Highway Safety Manual (HSM) calibration factors

ABSTRACTThe Highway Safety Manual (HSM) assists state and local agencies in improving highway safety by moving toward statistically proven quantitative analyses. The manual recommends using Empirical Bayes (EB) method with locally derived calibration factors to predict the agency's safety performance. It recommends deriving calibration factors using randomly selected 30 to 50 roadway sites that experienced a minimum of 100 crashes per year. Given the fact that the minimum sample size is a function of sample variance, this recommendation is clearly questionable as roadway characteristics of different roadway types are likely to have different levels of homogeneity. This research used Florida data to determine the minimum sample sizes to estimate reliable calibration factors for the following three facility types: rural two-lane roads, rural multilane highways, and urban and suburban arterials. The analysis was based on the data collected from more than 7,000 miles of segments and more than 1,000 intersections in Florida. The minimum sample size was determined such that there is a high probability that the calibration factor estimated from a sample is within 5% to 10% of the actual calibration factor calculated from the entire data set. For all the site subtypes, it was found that the minimum sample size of 30 to 50 sites, as recommended by the HSM, is insufficient to achieve the desired accuracy. Moreover, the sample sizes required for estimated calibration factors to lie within 5% of the actual calibration factors is almost double the sample sizes required for estimated calibration factors to lie within 10% of the actual calibration factors. The results also showed that the generalized one-size-fits-all approach of using a sample size of 30 to 50 sites is not appropriate as different facility types require different sample sizes depending on several factors, such as the extent of data variability, population size, crash experience, and so on, to estimate reliable calibration factors.

Exploration and comparison of crash modification factors for multiple treatments on rural multilane roadways

As multiple treatments (or countermeasures) are simultaneously applied to roadways, there is a need to assess their combined safety effects. Due to a lack of empirical crash modification factors (CMFs) for multiple treatments, the Highway Safety Manual (HSM) and other related studies developed various methods of combining multiple CMFs for single treatments. However, the literature did not evaluate the accuracy of these methods using CMFs obtained from the same study area. Thus, the main objectives of this research are: (1) develop CMFs for two single treatments (shoulder rumble strips, widening shoulder width) and one combined treatment (shoulder rumble strips+widening shoulder width) using before–after and cross-sectional methods and (2) evaluate the accuracy of the combined CMFs for multiple treatments estimated by the existing methods based on actual evaluated combined CMFs. Data was collected for rural multi-lane highways in Florida and four safety performance functions (SPFs) were estimated using 360 reference sites for two crash types (All crashes and Single Vehicle Run-off Roadway (SVROR) crashes) and two severity levels (all severity (KABCO) and injury (KABC)).The results of both before–after and cross-sectional methods show that the two single treatments and the combined treatment produced safety improvement. It was found that safety effects were higher for the roadway segments with shoulder rumble strips and wider shoulder width. It was also found that the treatments were more safety effective (i.e. lower CMF) for the roadway segments with narrower original shoulder width in the before period. However, although CMFs for multiple treatments were generally lower than CMFs for single treatments, they were similar for the roadway segments with shoulder width of 8–12 feet. More specifically, CMFs for single treatments were lower than CMFs for multiple treatments for the roadway segments with shoulder width of 9 feet or higher. Among different methods of combining CMFs, the HSM, Systematic Reduction of Subsequent CMFs, Applying only the most effective CMF, and Weighted average of multiple CMFs (Meta-Analysis) showed good estimates of the combined CMFs for multiple treatments with 2.2% difference between actual and estimated CMFs. The findings suggest that the existing methods of combining multiple CMFs are generally valid but they need to be applied for different crash types and injury levels separately.Lastly, an average of the combined CMFs from the best two methods was closer to the actual CMF than the combined CMF from only one best method. This indicates that it is better not to rely on only one specific existing method of combining CMFs for predicting CMF for multiple treatments.

Guidance on Customization of Highway Safety Manual for Virginia

For increased accuracy of the results of the procedures in the Highway Safety Manual (HSM), states have been encouraged to customize the procedures with local data. One way to customize the procedures is to develop calibration factors and to apply them to the default safety performance functions in the HSM. However, other ways can accomplish customization. The Virginia Department of Transportation (DOT) wants to customize the HSM procedures for the state as accurately as its resources will allow. This study examined ways to customize procedures and then developed guidance that could help a highway agency choose the best customization option for its jurisdiction. The guidance was used to recommend the best option for Virginia by using empirical data. The analysis was limited to divided segments and four-leg signalized intersections of rural multilane highways because the Virginia DOT's database provides most of the data required for developing safety performance functions and calibration factors for these two site types. The developed guidance flowchart can be used by an agency interested in customizing the HSM procedures. The flowchart can be applied with a combination of expert opinion and data analysis; a greater reliance on data analysis would require more time and resources. The guidance flowchart was applied in Virginia: a combination of Virginia's statewide safety performance functions, district-group calibration factors, and district-specific crash proportions appeared to be the best option for the state.

설계일관성을 반영한 감가속도 프로파일 개발 - 지방부 다차로도로를 중심으로 -

PURPOSES : Previous Speed Profile reflects the patterns of speeds in sections of tangents to curves in the roads. However these patterns are uniform of speeds and Acceleration/Deceleration. In oder to supplement these shortcomings. this study made a new profile which can contain factors of Acceleration/Deceleration through theories of Previous Speed Profiles. METHODS : For sakes, this study developed the speed prediction model of Rural Multi-Lane Highways and calculated Acceleration/Deceleration by appling a Polynomial model based on developed speed prediction model. Polynomial model is based on second by second. Acceleration/Deceleration Profile is developed with the various scenarios of road geometric conditions. RESULTS : The longer an ahead tangent length is, The higher an acceleration rate in curve occurs due to wide sight distance. However when there are big speed gaps between two curves, the longer tangent length alleviate acceleration rate. CONCLUSIONS : Acceleration/Deceleration Profile can overview th patterns of speeds and Accelerations/Decelerations in the various road geometric conditions. Also this result will help road designer have a proper guidance to exam a potential geometric conditions where may occur the acceleration/deceleration states.

New models to evaluate the level of service and capacity for rural multi-lane highways in Egypt

Multi-lane highways represent the majority of the total length of highway network in Egypt. The road geometry and the percentage of heavy vehicles (HVs) are considered the most important factors affecting the level of service (LOS) and capacity for any roadway. Therefore, this paper aims to explore the relationship between the road geometric characteristics and HV, and the LOS and capacity by two ways. First is the statistical modeling and second is the modeling by artificial neural networks (ANNs). In this research, the traffic and road geometric data are collected from mid-tangent points at 45 different sites that are located in desert and agricultural highways. The results showed that the ANN modeling gives the best models for estimating LOS and capacity. Also, it is better for analysis to separate the desert and agricultural sites. In addition, the most influential variables on LOS and capacity in desert sites are HV and lane width (LW), respectively, while in agricultural sites are LW and existence of side access (SA), respectively. These results are so important for road authorities in Egypt as they can determine LOS and capacity for different tangent sections and improve the traffic performance of them in the future.

Calibration of Highway Safety Manual Predictive Models for Oregon State Highways

The recently released Highway Safety Manual (HSM) published by AASHTO provides a comprehensive set of tools for evaluating and identifying opportunities to improve safety for highway facilities. Included in the HSM is a quantitative method for predicting crashes on the basis of recently developed scientific approaches. These predictive methods currently exist for three facility types: rural two-lane roads; rural multilane highways; and urban and suburban arterial highways. To enhance precision, each HSM predictive method should be calibrated for location conditions. This paper demonstrates the HSM calibration procedure for total crashes in Oregon. The research identified three critical data collection limitations on information about pedestrian volumes, minor road traffic volumes at rural locations, and minimum sample size for underrepresented crash locations. Most of the calibration factors for Oregon were determined to be considerably lower than the expected value of approximately 1, and this observation was attributed to Oregon crash reporting thresholds and procedures. The paper includes an evaluation of crash severity distribution methods and an assessment of the significance of collision type distributions on the overall predicted crashes.