Roadside Safety Research Articles

Benefits of Slope Flattening

The benefits of slope flattening were investigated by simulating accident costs with updated foreslope severities based on real-world accident data collected over a 7-year period in the State of Ohio. Functional classes considered were freeways, rural and urban arterials, and rural and urban local highways. Highways were modeled using the Roadside Safety Analysis Program (RSAP). Highway parameters considered in RSAP were slope steepness, roadway curvature, percent grade, longitudinal length, fill height, and lateral offset to the slope break point. Simulated accident costs were incorporated into a Microsoft Excel spreadsheet, where future users can specify installation costs, which tend to vary significantly from one location to another for slope flattening applications. Each functional class demonstrated slope flattening trends. On freeways and urban arterial highways, slopes should be no steeper than 1V:3H, and the benefit of flatter slopes was minimal. On rural arterial highways, the slope should be no steeper than 1V:4H, and the benefit of flatter slopes was also minimal. On local highways, the steepest slope should be 1V:3H, but the slope should be made as flat as possible because accident costs continued to decrease as the slope was flattened.

Correlation Between Crash Severity and Embankment Geometry

The severity of a roadside feature is often based on survey responses and has tended to emphasize extreme crash events, thereby overestimating the average severity of a particular feature. In this study, severity was related to embankment geometry by examining real-world accident data over a 7-year period. This was done by correlating the number of severe and fatal accidents to the exposure of particular slope geometries. Slope geometry was described by slope steepness and fill height, and its exposure was described by traffic volume and total unshielded mileage. Severity was adjusted for posted speed limits as well. The Roadside Safety Analysis Program (RSAP) was calibrated such that the distribution of severe injury and fatal accidents accurately reflected real-world data. Using this calibrated version of RSAP, the new severity indexes were studied and equations were created to correlate severity index to functional class, fill height, slope steepness, and posted speed limit. The local highway classification provided the highest severity, and the default severity used in RSAP was increased to accommodate this finding. Freeways, rural arterials, and urban arterials experienced reduced severity indexes relative to default values used in RSAP.

Conspicuity Research on the Highway Roadside Objects: A Simulator Study

In a monotonous travelling environment, the single-vehicle run-off-roadside accidents occur easily. The injuries and fatalities caused by those accidents are significant components of the annual road casualties. The causation is the complex interaction of the visual effects on the roadside objects’ conspicuity. So the conspicuity enhancement needs to be considered in the roadside objects design to provide a temporary restoration of alertness and vigilance to drivers. Factors contributing to the conspicuity of the roadside objects were analyzed in this paper. A driving simulator study was conducted in order to extrapolate the relationship between the legibility distances and the objects and to quantify the conspicuity of the roadside objects different in basic features. The conclusions of this paper were firstly, a significant correlation existed between the mean legibility distance and the object’s size. The mean legibility distance was in a significant exponential proportion to the object’s size. Secondly, the triangle’s legibility was better than that of the rectangle and round contours. Only when the roadside object was combined with the suitable contour and size did the best visual quality come. To some extent, the conclusions could provide theoretical tools and strategies to optimize the dimensional design of the roadside objects in order to maintain the roadside safety.

Selection Table Development for Bridge Railing

Although six test levels have been available for 20 years to develop a longitudinal barrier, guidelines on how to choose bridge railings on the basis of specific site and traffic conditions have not been developed that take advantage of the range of crash-tested bridge railing hardware. The research reported in this paper was performed to develop such guidelines. During the guidelines’ development, several important issues emerged that quantified how the site, traffic, and cost characteristics of a project site should be characterized. This paper presents the issues and discusses the applied solutions. A sample set of bridge rail selection tables is presented with use of the solutions discussed, and the sample is compared with bridge railing selection tables documented in the literature. Although the specific example discussed in this paper involves the selection of bridge railings on the basis of site and traffic conditions, the same procedure can be used to develop most other roadside safety selection and location tables.

Method for Modeling Crash Severity with Observable Crash Data

This paper presents a new method to rank the severity of an impact with a roadside hazard that is based on observable crash data. This method has been incorporated into the third update of the Roadside Safety Analysis Program. The equivalent fatal crash cost ratio (EFCCR) is a dimensionless value that represents the severity of a crash on a scale of zero to unity, where zero represents no chance of injury and unity represents absolute certainty of a fatal injury. The method uses a census of police-reported data, which ideally covers a range of speed limits. The purpose is to determine the severity distribution of crashes in cases in which no events preceded the crashes with the hazard under evaluation and which did not result in a penetration or a rollover. The number of unreported crashes is estimated and added into the severity distribution with the assumption that the number represents crashes that led to property damage only. The average expected crash cost is then calculated and normalized to a reference speed of 65 mph so that it is directly comparable to EFCCR values calculated for other types of hazards. Unlike the earlier subjective severity index method, the new EFCCR method has its basis in observed crash data and uses a systematic approach to calculate crash severities that can be used in benefit–cost and other safety analyses.

Understanding of Heavy-Vehicle Encroachment Frequency

Encroachment data gathering in the past explicitly excluded heavy vehicles; this exclusion compelled assumptions to be made about the frequency at which heavy vehicles encroached onto the roadside. This paper examines the assumption that heavy vehicles encroach onto the roadside at the same rate as passenger vehicles. This assumption may be untrue for several reasons. In general, heavy vehicles are driven by trained professionals, who operate with additional restrictions on operating hours. Driver behavior and the performance characteristics of heavy vehicles differ from those of passenger vehicles. In this study, four data sets were analyzed: a national sample, two statewide samples, and a regional sample. The results challenged the long-held assumption that heavy vehicles encroached at the same frequency as passenger vehicles. The findings indicated that heavy vehicles encroached at approximately 30% of the rate of all vehicles. Although the causes of this reduced encroachment rate remain speculative, the examined data demonstrate that a difference does exist and should be accounted for in the modeling of run-off-road crashes for roadside safety benefit–cost and risk analyses.

Decision-making Model of Roadside Safety Improvement on Two-lane Highway

In order to meet the needs of scientific decision-making of roadside safety improvement project, a decision-making model of two-lane highway roadside safety improvement is proposed which based on Game Theory analysis. Firstly, roadside safety level was divided by indicators which can reduce the probability of run-into-roadside or improve the safety of roadside objective characteristics, and each indicator safety classification standards was determined on the basis of certain statistics data. Then, countermeasures database of roadside safety improvement is established by summarize and refining the roadside safety conditions countermeasures based on the domestic and overseas research results. Finally, against Game problems for roadside safety improvement process, and carried out the analysis of conflict and cooperation about the Game problems, decision-making information fusion model of roadside safety improvement is proposed by Game Theory. The results can provide a decision-making method for roadside safety improvement program.

Safety Enhancement of Water‐filled Road Safety Barrier using Interaction of Composite Materials

Road safety barriers are used to redirect traffic at roadside work-zones. When filled with water, these barriers are able to withstand low to moderate impact speeds up to 50kmh-1. Despite this feature, there are challenges when using portable water-filled barriers (PWFBs) such as large lateral displacements as well as tearing and breakage during impact, especially at higher speeds. In this study, the authors explore the use of composite action to enhance the crashworthiness of PWFBs and enable their use at higher speeds. Initially, we investigated the energy absorption capability of water in PWFB. Then, we considered the composite action of a PWFB with the introduction of a steel frame to evaluate its impact on performance. Findings of the study show that the initial height of impact must be lower than the free surface level of water in a PWFB for the water to provide significant crash energy absorption. In general, impact of a road barrier that is 80% filled is a good estimation. Furthermore, the addition of a composite structure greatly reduces the probability of tearing by decreasing the strain and impact energy transferred to the shell container. This allows the water to remain longer in the barrier to absorb energy via inertial displacement and sloshing response. Information from this research will aid in the design of next generation roadside safety structures aimed to increase safety on modern roadways.

An In-Depth Investigation of Roadside Crashes on Thai National Highways

Road crashes in Thailand cause some 13,000 deaths each year. About 12% of these occur on national highways under the jurisdiction of the Department of Highways (DOH). For the past four years, 2007-2010, roadside crashes have constituted between 42.2 - 47.9 %, averaged 44% of the total crashes on the DOH's highways. This paper presents the result of in-depth roadside crash investigations with the aim of improving the roadside safety situation in Thailand. It was found that speeding was the main human error that contributed to the crashes, accounting for 57% of the causes. The cases involving vehicle hitting trees, the most common roadside hazard in Thailand, were found to be the most serious and common roadside crashes accounting for 72% with resulting 48 fatalities. The paper gives details of the investigation into the cause and consequences of these crashes. The authors urge DOH to take needed actions on the proposed strategies to deal with this immensely serious problem. The strategies are based on the DOH Roadside Safety Strategic Plan 2009-2013.

The Crash Mechanics of Fatal Motorcycle–Barrier Collisions in Australasia

Motorcyclists contribute significantly to road trauma around the world through the high incidence of serious injuries and fatalities. The role of roadside safety barriers in such trauma is an area of growing concern among motorcyclists, road authorities, and road safety researchers and advocates. This article presents a case series analysis of motorcyclists that were fatally injured following a collision with a roadside barrier during the period 2001 to 2006 in Australia and New Zealand. The crash mechanics of the fatal motorcycle–barrier collisions are detailed, with the aims of providing an understanding of the manner in which these types of crashes occur, informing motorcycle–barrier crash test protocols, and for crash reconstruction purposes. The detailed descriptions of the mechanics of the crashes include barrier and motorcycle types, crash postures, motorcyclist kinematics, precrash speeds, impact trajectory angles, and motorcyclist kinetic energy dissipation on the barrier. Recommendations are made with regards to appropriate motorcycle–barrier crash test protocols.

충격흡수 세이프티롤러 가드레일의 탑승자 위험도 해석

PURPOSES: This paper presents the results of computer simulations of roadside safety barrier, called by safety roller guardrail, consisting of rotational roller, rotation control plate, post and subsidiary members. The rotation roller and rotation control plate are made by EVA(ethylene vinyl acetate), and PE(polyester), respectively. METHODS: The occupant risk analysis has been carried out under vehicle crash condition for high containment level of SB-4 for the purpose of local road. Simulations are performed with the finite element code LS/DYNA-3D. RESULTS: The numerical results obtained by LS/DYNA-3D software from the viewpoints of vehicle stability, vehicle trajectory, occupant risk, etc. CONCLUSIONS: It is noted that not only impact severity is drastically reduced but also vehicle trajectory is improved due to the characteristics of energy absorption and rotation pattern of EVA rollers connected by control plates.

Analysis of Roadside Safety of Highways in South Thailand

Every year, the number of road crashes in Thailand, which result in about 12,000 deaths, has been around 1 million. About 12% of these crashes occur on national highways under the jurisdiction of the Department of Highways (DOH). For the past four years, 2007- 2010, roadside crashes have constituted between 42.2 - 47.9 % of the total crashes on the DOHA's highways. On average there is about 12000 crashes on Thai national highways and roadside crash accounts 5900 cases or 44%. This paper describes the roadside crash situation on Thai highways by using DOH records of 949 crashes that occurred during 2007-2010 on 270 km. section in Southern Thailand. The results show that speeding vehicles are more likely to be involved in roadside crashes accounting for about 70% of the crashes. Among all passenger vehicles (passenger cars, vans, pickups, and songtaews (converted passenger pickup), pickups are more likely to be involved in roadside crashes as compared to other passenger vehicle types. Detailed investigation of in-depth roadside crashes is also described. The DOH has started actions the roadside tree problem, a description of the action is described the DOH Roadside Safety Strategic Plan 2009-2013.

Influence of Land Use and Driveway Placement on Safety Performance of Arterial Highways

Characterizing driveway safety is a relevant and relatively complex topic in transportation safety research. This research studied the safety link of driveways abutting Oregon highways and considered various factors proposed in the current literature for design and evaluation of the safety performance of roadside elements. On the basis of two probability samples from rural and urban arterial state highways, this research developed alternative safety performance functions to evaluate the safety impacts of various driveway configurations. These safety performance functions were intended to explore driveway safety beyond the average driveway density treatment commonly encountered in the literature. The statistical models and methodologies in this research are comparable with those in the Highway Safety Manual. The proposed models exhibited different ranges of effects for urban and rural conditions, but type of land use proved a prominent factor for both the urban and the rural models. The analysis showed that roadside safety is influenced mainly by driveways associated with commercial and industrial land uses in the urban environment. Similarly, industrial driveways are more influential for safety than other types in rural environments. In addition, the rural model uncovered a safety connection to clusters of driveways rather than to driveways alone. This research indicated that after driveway land use in rural environments was accounted for, clustered driveways tended to have fewer crashes compared with isolated driveways.

Investigation of a series of relevant phenomena for modelling the full-scale crash test of a small vehicle with a guardrail system

Computer simulations have become a common tool in roadside safety to predict the kinematics and dynamics of a vehicle impacting against restraint systems before full-scale crash tests are performed. Given the typical large size of the full-scale hardware, to maintain feasible simulation periods, vehicle models have to be limited to the relevant physical phenomena necessary to properly reproduce the reality under investigation. Hence, an accurate identification of these phenomena is crucial. This paper identified a series of physical phenomena not previously investigated, which have been found to play a relevant role for successfully modelling an impact between a small vehicle and a guardrail system. An analysis of the specific role for each of the investigated phenomenon is provided along with conclusions about which phenomena are necessary to model in order to properly simulate a full-scale crash test against a guardrail system. Indications for future investigation are suggested as well.

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.

소형차 전용도로를 위한 콘크리트 차량방호울타리의 동적성능 평가

PURPOSES : In This study two different concrete barrier systems have been proposed to be established at the small vehicle driveway. One is for median barrier, and the other is for roadside barrier. METHODS : In order to determine the suitable shape of barrier, the impact parameters including vehicle weight, impact angle, impact velocity and impact level have been analyzed. The real crash test has been carried out with 0.9 ton and 2.5 ton vehicles, respectively by using the 2m segment type concrete barriers connected by steel plates that are totally 40m barrier systems. RESULTS : The numerical results obtained by LS/DYNA-3D software are compared with real crash tests from the viewpoints of vehicle stability, vehicle trajectory, occupant risk, etc. CONCLUSIONS : From the above results, the dynamic performance of proposed barrier systems satisfies the specification of Korean Code for roadside safety structures.

충격흡수시설에 대한 특정 충돌시험데이터의 확대해석

충돌해석 데이터의 확대해석 사례는 미국의 도로안전시설 지침인 MASH(Manual for Assessing Safety Hardware, AASHTO, 2009)에서 2,270 kg 픽업트럭의 충격흡수시설에 대한 충돌시험 데이터로부터 1,500 kg 중형승용차의 안전도를 계산하는 절차에 관한 내용을 최초로 소개하였다. MASH 방법에 따라 1.3 ton 차량의 충돌시험 데이터로부터 0.9 ton 차량의 충돌데이터 및 안전지수를 계산하여 0.9 ton 차량의 충돌실험 데이터와 비교하였다. 비교 결과 MASH방법으로 계산한 0.9 ton 차량의 충돌데이터 및 안전지수가 충돌실험 데이터와 큰 차이를 나타낸다는 것을 확인하였고 그 원인을 분석하여 새로운 확대해석 방법을 개발하였다. 개발된 확대해석 방법은 질량이 큰 차량(1.3 ton)의 충돌시험 데이터로부터 작은 차량(0.9 ton)의 충돌 데이터를 계산할 수 있을 뿐 아니라 작은 차량(0.9 ton)의 충돌 데이터로 부터 큰 차량(1.3 ton)의 데이터를 계산할 수 있다. 개발된 확대해석 방법은 정확도가 MASH에 비하여 월등하고 이론적인 원리가 확실하다. 본 논문은 충돌시험 데이터를 이용하여 새로운 확대해석 방법의 효율성과 정확도를 입증하고 그 원리를 규명하였다. It is found the first case of broad interpretation of the crash analysis in MASH (Manual for Assessing Safety Hardware, AASHTO, 2009) which is the guideline of roadside safety features in United States. They introduced the procedure of calculating 1,500 kg sedan safety index from the 2,270 kg pick-up truck crash test for crash cushion. First, following MASH's method, calculate 0.9 ton vehicle crash data and safety index using 1.3 ton vehicle crash test data and compare with actual 0.9 ton vehicle crash test data. results show that actual test data and the data calculated by MASH's method have great difference. Second, analyse the cause and develop new method. Proposed method can estimate not only the lighter vehicle (0.9 ton) crash data from the heavier vehicle (1.3 ton) crash test but also heavier vehicle (1.3 ton) data from lighter vehicle (0.9 ton) test. This method is superior to MASH's method and has stronger theoretical foundation. This paper proves the efficiency and the accuracy of new broad interpretation method using crash test data and investigates the principle.

The development of an enhanced finite element tire model for roadside safety hardware assessment

Various types of roadside safety hardware are deployed along highways to safely redirect or contain errant vehicles such that there is no intrusion into a hazardous area or on-coming traffic that may cause harm to the drivers or occupants. Primary factors for the crashworthiness evaluation of these hardwares include structural adequacy, occupant risk, and after-collision vehicle trajectory. Suspension characteristics of the vehicle and tires interaction with safety hardware and surface conditions could influence all these factors. Simulation efforts have resulted in increasingly better replications of crash events, but it has been noted that tire behaviors and failures are still not predicted well. This article will describe efforts to improve the finite element modeling technique of a vehicle tire. A new tire model, having the physical structure of a tire that could influence the nature of operational and crash-induced loading of the tire is presented. Techniques for characterizing the tire material and suspension properties are discussed. Correlation between the simulation results and the full-scale crash testing data is discussed. Measures for assessing occupant injury risk and occupant impact severity are evaluated for both sets of data. Finally, preliminary results using the new tire model in vehicle impact simulations to investigate the effect on vehicle stability, subject to variations in impact conditions such as speed and angle, are presented.

Transition of Temporary Concrete Barrier

The objective of this research was to design a transition from temporary concrete barriers to a permanent concrete barrier for median applications. The researchers at Midwest Roadside Safety Facility utilized a combination of free-standing and tied-down Kansas temporary concrete barriers and a dual-nested thrie beam for the transition to the single-slope permanent barrier as well as a transition cap. Two full-scale vehicle crash tests were performed on the system. Evaluation of the approach transition required testing at two Critical Impact Point (CIP) locations. The first tests was performed using a half-ton pickup truck that impacted the temporary barriers 1,432 mm upstream from the permanent barrier, at a speed and angle of 100.7 km/h and 24.7 degrees, respectively. The second crash test was also performed using a half-ton truck that impacted the temporary barriers 16.6 m upstream from the permanent barrier, at a speed and angle of 100.1 km/h and 26.2 degrees, respectively. Both tests were conducted and reported in accordance with requirements specified in the Manual for Assessing Safety Hardware (MASH) and were determined to be acceptable according to the Test Level 3 (TL-3) evaluation criteria.

Evaluating safety risk of locating above ground utility structures in the highway right-of-way

Roadside safety has been a concern for highway engineers and designers for many decades. A significant part of this concern is related to collisions with utility poles. Current practices and standards for placing utility poles are based on a combination of qualitative guidelines/heuristics and relatively outdated findings. Accordingly, there is a need to study the safety level associated with placing utility poles at different lateral offsets from the edge of the travel-way. In this paper a Safety Performance Function (SPF) is developed to relate roadway and roadside variables to utility pole collision frequency. It was found that increasing the poles offset has a more significant effect on reducing the frequency of utility pole collisions compared to increasing poles spacing. Based on the developed utility pole-SPF, design charts were provided to facilitate calculations and decision-making process. The developed utility pole-SPF was compared to a widely-used utility pole collisions model and the differences in the type of data and the development methodology were highlighted.