Road Restraint Systems Research Articles

Design Principles to Reduce Vehicle Pocketing at Guardrail-to-Concrete Barrier Transitions

Road restraint systems (RRSs) on European roads are provided by several manufacturers and, hence, lead to differences in geometry, material, and mode of operation. Focusing on the combination of soft steel RRSs with relatively stiffer concrete RRSs, it is vital to consider the potentially critical deformation kinematics during vehicle impacts, such as vehicle pocketing. Since a statutory test procedure was not introduced until mid-2024, much of the transition construction (TC) on Austrian roads has remained untested. Knowledge of the design features to be implemented during the refurbishment of such TCs is of great interest. The main focus of this study was to derive constructive measures (CMs) that increase traffic safety and are applicable to various TCs already installed on roads. The first step involved deriving design principles whose implementations in TCs reduce the risk of critical vehicle or RRS behavior. Based on finite element simulations, the functionality of a TC featuring all derived design principles was examined. The effect of each individual CM was analyzed in a parameter study. The results from a TB61 impact simulation on the derived TC showed the effectiveness of CMs, achieving smooth vehicle redirection. Vehicle pocketing was limited to a minimum, and neither penetration of the TC nor rollover of the vehicle was observed. The analysis of the influence of each CM indicated positive, and in some cases, negative effects. The working width was mainly positively influenced by the compaction of the posts, an additional steel bar, and the chamfering of the first concrete element. A rather diverse picture is drawn regarding the influence on the tensile forces in the guardrails. Some CMs had both positive and negative effects on the distribution of forces in the upper and lower guardrails. Nevertheless, all CMs had positive effects on the tensile forces in the coupling. The chamfering of the first concrete element was the most effective measure to prevent vehicle pocketing. However, through the combination of all CMs, the positive effects predominated, ensuring the functionality of the TC as a whole. This study provides basic insights into the effectiveness of constructive measures, which can serve as a reference for the renovation of in-service TCs or in the development phase of new TCs to be certified.

Nonlinear dynamic finite element analysis of vehicle impacts into road restraint systems

Despite that the safety of cars is continuously increasing, improving the safety of road transportation remains a key issue of modern society. The design of suitable road restraint systems plays an important role. As the tests of barriers are technically demanding and expensive, and road traffic intensity is continuously growing, it is crucial to develop advanced models that would make it possible to explore various scenarios under which road vehicles may accidently impact into the road restraint barrier. The submitted study focuses on the use of nonlinear dynamic finite element analysis (NLDFEA) in the reliability assessment of road restraint systems, with a particular focus on steel barriers subjected to impacts by heavy vehicles. The outcomes of theoretical analyses are compared with the results in a compiled unique database of full-scale road barrier impact test results. It appears that a good match between crash test results and the validated NLDFEA model can be achieved, differences being mostly within a range of 10 %. When modelling the crashes of buses and HGVs, it is particularly important to model correctly shape and geometry of the front and impacting side of the vehicle, tyre sizes, wheelbase and overall truck dimensions, and position of the centre of gravity of the vehicle including trailer and cargo. Recommendations for subsequent research studies and for practical applications are finally provided.

Correlation of Road Safety Criteria with Occupant Safety Criteria in Impacts on Crash Cushions

Road restraint systems are used to protect vehicle occupants if the vehicle runs off the road and potentially collides with a dangerous obstacle. These road restraint systems must successfully pass the tests defined in EN 1317, or the Manual for Assessing Safety Hardware (MASH) before they are allowed to be installed. The safety assessment is carried out according to the criteria of ASI (Acceleration Severity Index), THIV (Theoretical Head Impact Velocity), OIV (Occupant Impact Velocity), ORA (Occupant Ridedown Acceleration), and PHD (Post-Impact Head Deceleration). Usually very old vehicles are used for these tests, and there is no assessment of occupant criteria such as HIC (Head Injury Criteria), chest deflection, etc. The objective of the study was to compare the occupant safety of vehicles that are commonly used in EN 1317 with vehicles that have improved safety equipment. Test results from two different vehicles (a commonly used vehicle in EN 1317 and a vehicle with improved safety equipment) and two different impact conditions (full overlap and an overlap of 50%) were compared. Measurement data from a Hybrid HIII 50th percentile anthropomorphic test device (ATD) (Denton ATD, INC.) was recorded during the tests to assess occupant safety. The tests have shown that vehicles with improved safety equipment perform better than vehicles that are commonly used in EN 1317-3 tests. The values for the occupant safety criteria assessed were well below the Euro NCAP (New Car Assessment Programme) or Federal Motor Vehicle Safety Standard (FMVSS) limits. However, the limits of the road safety criteria were in some cases considerably exceeded regardless of the vehicle. This has been observed in particular for the offset impact condition. THIV and OIV were supposed to be able to assess the risk of head injuries. However, these two criteria correlated negatively with the head criteria, HIC or a3ms. However, a positive correlation was found for the ASI with the HIC and the a3ms head acceleration. Even if some of the criteria for road safety correlate with the criteria for occupant safety, it is doubtful whether the criteria for road safety are suitable for assessing the risk of injury to vehicle occupants.

Numerical modeling of the effects of impact conditions, foundation stiffness, and cable pretension on the behavior of high-tension guard cable systems

Cable barriers are one type of road restraint system commonly used on highways across the United States to contain and redirect errant vehicles and to prevent crossover accidents. These systems are typically tested under the provisions from safety manuals considering standard crash conditions (e.g., vehicle speed and impact angle). To understand the performance of cable barriers, it is important to evaluate the effects of non-standard crash and system conditions, including various vehicle speeds, impact angles, foundation material stiffness, and cable pretension loads. For that purpose, we created a set of full-scale finite element models in LS-DYNA to assess the effects of these non-standard conditions on the performance of high-tension cable barrier systems. The results from the models show that soft soils and under-tensioned systems yield higher cable deflections. Moreover, the results indicate that speeding vehicles colliding at non-standard angles increase cable tensions by up to 91% and cable deflections by up to 318%. These findings highlight the importance of evaluating cable barrier performance under more severe scenarios, which could lead to system failure and more severe collision consequences.

Crashworthiness of the bollard system by experimentally validated virtual test

Shielding risky/vulnerable roadside zones in urban areas such as playgrounds, sidewalks, bus stations, oil/gas stations, and regulators of infrastructure facilities has been a significant focus point by engineers and local authorities in recent decades due to the boost of vehicular number and mobility. Bollard systems are regarded as one of the efficient countermeasures, especially for the zones that vehicles and pedestrians share. This paper discusses the performance of a steel bollard system by experimentally validated virtual crash tests following IWA 14-1 (Vehicle security barriers (VSB): Performance requirement, vehicle impact test method and performance rating), EN 1317 (Road Restraint Systems), and EN 16303 (Validation and verification process for virtual testing in crash testing against vehicle restraint system) standards. In this context, pendulum crash tests were performed, virtual pendulum crash tests were verified and modelled with the results of actual tests then full-scale virtual crashworthiness tests were conducted respectively. The penetration, Acceleration Severity Index (ASI), displacement, and deformation values of the bollard system were evaluated considering the relevant standards and the characteristics of urban traffic. Based on virtual test results with increased reliability, the bollard system has the capability to shield the roadside critical assets against M1 class 900 kg vehicles up to 50 km/h and M1 class 1500 kg vehicles up to 32 km/h.

A Unified Approach for Risk Assessment of Road Crash Barriers Using Bayesian Statistics

The aim of this article is to improve road safety. Specifically, it deals with the development of a mathematical model that will more accurately define the severity of a defect in a road restraint system. Currently, that evaluation is based only on the subjective perception of individual safety auditors. The mathematical model was developed based on the principle of Bayesian statistics. The determination of the specific risk was made by comparing the results of the model for two datasets. In the first case, the model was based on accident data correlated with recorded defects in road restraint systems. In the second case, the dataset represented accident events with crash barriers where no defect was identified. Based on the comparison, a total of 64 risk combinations were identified. The mathematical model confirmed 26 combinations (41% of all selected combinations of the defect levels of the crash barriers). Although not even half of the identified combinations were confirmed, more than 90% of all correlated records are found in these exposures of confirmed combinations. The verification was able to clearly define the risk of safety defects and thus brings potential accuracy to subsequent decision-making related to the repair of road restraint systems.

Assessing Roadside Hybrid Energy Absorbers Using the Example of SafeEnd.

A combination of crash cushion and end-terminal, hybrid energy absorbing devices have been in use worldwide for a few years already. They include SafeEnd, a system Poland has recently introduced. Some road authorities have raised concerns as regards the operating conditions of the devices and how they work together with safety barriers. The objective of this research is to clarify the concerns and answer the following questions: (1) Can SafeEnd devices be used as hybrid devices and combine the roles of end-terminal and crash cushion placed before an obstacle? (2) What should be the rules for installing crash cushions at diverging roads and at the start of an off-ramp? The article presents characteristics of SafeEnd devices, defines the doubts raised by road safety auditors, discusses the results of field and numerical tests of the devices and explains the design principles for interchange ramps where crash cushions are required. The study results have helped to answer the research questions: SafeEnd devices fulfil the role of end-terminal and crash cushion, it is possible to make them more visible and principles have been defined for how the devices should be used at road interchanges. Further research should help to define general principles of deploying road restraint systems such as crashworthy terminals, crash cushions or hybrid devices.

APPLICATION OF RSA PRINCIPLES TO IMPROVE THE BIM IN THE ROAD DESIGN PROCESS WITH FOCUS ON THE ROAD RESTRAINT SYSTEMS

Abstract. Sustainability is one of the main scientific and public topics of today. This includes the sustainable transport and infrastructure. One of the ways how to achieve higher level of sustainability is through the implementation of BIM (Building Information Modelling) into the road design process. However, to create a safe road network, which is also necessary for achievable sustainability, it is essential to consider the Road Safety Audit (RSA) principles throughout the BIM applications. The paper discusses the possibilities of involving the RSA in the process road design in I-BIM (Infrastructures Building Information Modelling). Within the individual phases of the preparation of a transport project and the application of the safety audit tools in BIM applications, it is possible to achieve a significant increase in the level of safety. This approach is shown within the paper on the implementation and use of supplementary road safety devices, specifically the road restraint systems. Currently, the individual components are defined by their main parameters in specific libraries. However, their definition is only as a general object where many of the supplementary parameters or fundamental design characteristics, such as working width or minimal length, are not included. This may lead to potential design flaws or safety hazards which have to be subsequently corrected in further phases. The objective of the paper is to identify the current deficiencies, primarily the missing road safety perspective within the BIM process. The aim is to enable appropriate selection of safety equipment during the design or to provide sufficient information for the mandatory RSA.

Experimental performance evaluation of an innovative hybrid barrier system filled with waste materials

Roadside barriers have been one of the main contributors to reducing fatal traffic accident severities. There is limited knowledge about the potential for using natural/waste materials for roadside barrier applications. This paper aims to develop a novel hybrid roadside barrier type by using timber and waste materials (slag and tire) together and to observe the performance. In this regard, pendulum crash tests were conducted and deformation, working width, and severity performance of each hybrid barrier type were evaluated following EN 1317 road restraint systems standard. Experimental results revealed that hybrid barriers produced with waste materials can be alternative to conventional barriers. They can be recommended to place, especially in scenic, mountainous, and historical roadsides due to their aesthetic design and environmentally friendly features. This is the first step towards enhancing innovative hybrid barriers and will serve as the basis for the next step, full-scale crash tests. Outcomes of this study will encourage the utilization of different waste materials in the production of roadside barriers in future studies and contribute to the diversification of utilization areas of waste materials.

The development of standards for road restraint systems

The article discusses requirements for road restraint systems, gives recommendations for their classification, formulates the requirements for layout of cameras for recording tests, proposes a method for determining the values of the dynamic deflection and the working width of the road barriers. This work proposes a classification of road barriers; gives the estimates of the influence of tolerances in weight and collision speed of a vehicle in the field tests of road barriers on the values of dynamic deflection and the working width; introduces the concept of category for the dynamic deflection and working width of a barrier; supplements the testing methods for different types of road barriers.

An innovative approach on the renewable hybrid barrier: combined use of wood and sand

ABSTRACT Background: Wooden materials have been among the basic materials used in many different areas due to some advantages throughout the history. Roadside barriers, which are called passive safety structures, can be produced with different materials such as wood, steel, concrete, and plastic. In this study, Renewable Hybrid Barriers (RHB), a new type of barrier that is used wood in terms of aesthetics, renewability, high shock resistance, and used sand in terms of impact absorption capacity and low cost, produced by taking into account some of the disadvantages of other barrier types. These barriers are planned to be used especially in historical/touristic areas, scenic roads, and in urban areas as urban furniture. Real-time crash tests in accordance with EN 1317 (Road Restraint Systems) standard require high cost and long time. Therefore, the pendulum crash test mechanism frequently used in the literature was manufactured at which the experiments were carried out. Results: The results revealed that the RHBs which has 2 cm thick timber and sand used together, were sufficient and suitable in terms of both cost and necessary safety criteria. It was observed that impregnation and heat treatment applications did not have a considerable negative effect on the performance of RHBs which provide an opportunity to use RHBs for outdoor conditions.. Conclusion: In the light of the results of the study, the optimum wood timber thickness was determined as 2 cm regarding TB 31 test criteria. It is proposed that the crash tests for different wood species, timber thickness, and/or barrier dimensions should carry out in future studies. This study can serve as the basis for the next step, real-time real crash tests. Since the study includes an interdisciplinary subject, it is thought that it will inspire different studies.

The role of numerical tests in assessing road restraint system functionality

Key to understanding the needs and building road infrastructure management tools to prevent and mitigate run-off-road accidents is to identify hazards and their sources which are a result of wrong design, construction, and installation of road restraint systems. Building such tools requires advanced studies with field tests, simulations and models to demonstrate the effects of selected parameters on road user safety. The research work included building numerical models which were validated with crash tests and mathematical models to assess the effects of selected parameters on the safety and functionality of devices. Twenty five field tests were the basis for conducting 670 numerical tests. Preliminary results of numerical tests are also presented looking at selected problems such as barriers on curves, presence of kerbs and obstacles within barrier working width. The methodology will help with an optimal selection of parameters leading to improved safety as regards errant vehicles.

Mechanical and microstructural evaluation of high performance steel (S700MC) for road restraint systems

The suitability of using high performance steel (S700MC) for road restraint systems (RRS) under very high containment level was evaluated in this study. To investigate the influence of the crash on the mechanical behaviour of the steel, different test pieces were tested by tensile and hardness testing, and examined by scanning electron microscopy (SEM). The tensile test results of S700MC showed a noticeable increase in yield strength at 0.2% elongation (Rp0.2) from 744 to 935 MPa, and ultimate tensile strength (UTS) from 810 to 1017 MPa, before and after crash tests (BC and AC, respectively). S700MC showed ~9% lower elongation at fracture value in comparison with S275JR and S355JR steels. Besides, fracture toughness, was significantly higher for S700MC (133 and 148 MJ/m3 for BC and AC, respectively) compared to conventional mild steels (108–118 MJ/m3). Microstructural observations of head-part of all S700MC samples revealed equi-axed grains. The fracture surface of tensile tested samples before crash, showed elongated grains accompanied by pore formation. Among after crash samples, one test piece showed intergranular cracks while no intergranular cracks were observed for the other crashed pieces which resulted in the lower Rp0.2 (813 MPa) and UTS strength (847 MPa) and fracture toughness (125 MJ/m3). The results showed that although RRS manufactured with S700MC undergoes severe mechanical deformation, the risk of brittle fracture is very low and this is beneficial from industrial as well as social point of view.

Innovative Research Into Road Restraint Systems

Abstract Key to understanding the needs and building road infrastructure management tools to prevent and mitigate run-off-road accidents is to identify hazards and their sources which are a result of wrong design, construction, installation and maintenance of road restraint systems [1]. Building such tools requires advanced studies with field tests, simulations and models [30]. Delivered under the Road Innovation programme, two research projects (ROSE and LifeROSE) are designed to help with that. The main aim of the projects is to develop a method to help with an optimal choice of road restraint systems.

Experimental and numerical analysis of the modified TB32 crash tests of the cable barrier system

Road restraint systems, including safety barriers, are one of the means used to improve road safety. Currently, they can be allowed to general use after passing the specific crash tests. However, it is always important and desirable to evaluate their performance under various realistic conditions, which can happen on the roads. In this study, the behaviour of the cable barrier system in impact conditions different than assumed by EN 1317 standard was analysed. For this purpose, a full-scale crash test was performed and on the basis of this the validation process of numerical simulations was carried out. Correctly and carefully developed numerical simulations give unique insight into the impact mechanism and allows for comprehensive understanding of barrier responses. The accuracy of the numerical models was assessed by comparing the results of the simulation with the crash test. The research showed that the analysed barrier work correctly, it contained and then properly redirected 1500 kg car back onto the road and ensured safety for the vehicle occupants at the same time.

Radial basis function surrogate model-based optimization of guardrail post embedment depth in different soil conditions

For guardrail designers, it is essential to achieve a crashworthy and optimal system design. One of the most critical parameters for an optimal road restraint system is the post embedment depth or the post-to-soil interaction. This study aims to assess the optimum post embedment depth values of three different guardrail posts embedded in soil with varying density. Posts were subjected to dynamic impact loads in the field while a detailed finite element study was performed to construct accurate models for the post–soil interaction. It is well-known that experimental tests and simulations are costly and time-consuming. Therefore, to reduce the computational cost of optimization, radial basis function–based metamodeling methodology was employed to create surrogate models that were used to replace the expensive three-dimensional finite element models. In order to establish the radial basis function model, samples were derived using the full factorial design. Afterward, radial basis function–based metamodels were generated from the derived data and objective functions performed using finite element analysis. The accuracy of the metamodels were validated by k-fold cross-validation, then optimized using multi-objective genetic algorithm. After optimum embedment depths were obtained, finite element simulations of the results were compared with full-scale crash test results. In comparison with the actual post embedment depths, optimal post embedment depths provided significant economic advantages without compromising safety and crashworthiness. It is concluded that the optimum post embedment depths provide an economic advantage of up to 17.89%, 36.75%, and 43.09% for C, S, and H types of post, respectively, when compared to actual post embedment depths.

Road Restraint Systems as a Basis for Roadside Safety Improvement

Roadside-related crashes occur when vehicles run off the road. The majority of the crashes have severe outcomes, especially when an object is hit (tree, pole, supports, front wall of a culvert, barrier). These accidents represent app. 19% of all of Poland’s road deaths. Roadside crashes involve: hitting a tree, hitting a barrier, hitting a sign or utility pole, vehicle roll-over on the roadside, vehicle roll-over on a slope and vehicle roll-over into a ditch. Understanding the effects of roadside factors on road safety requires in-depth research. The problem was partly addressed at the WMCAUS conference in 2017 [1]. Key to understanding the needs and tools of road infrastructure management for preventing run-off-road crashes or minimising their consequences is to identify the hazards and sources of hazards caused by wrong or improper use of road safety devices. It is also important to identify errors in the design, structure, construction and operation of road safety devices. Studying such an extended scope of the problem required fieldwork. Site tests had to be conducted such as hitting a wire rope barrier and a steel barrier on curve (test TB32), light and heavy vehicles hitting a bridge parapet (tests TB11 and TB51), hitting a transition between a steel and wire rope barrier (TB32) and crashes into a lighting column placed within the barrier’s working width. In addition, the project includes numerical tests validated on the basis of site tests. This helps to assess the behaviour of road restraint systems when selected parameters are changed. The work is part of the RID Programme (Development of Road Innovation) and the RoSE project (Road Safety Equipment). In the article the authors present the effects of building a road restraint system database for a selected test site (about 3,000 km of Poland’s national roads). An outline of new road restraint system guidelines could only be developed after understanding the effects of restraint systems, the design, additional elements, type of road and safety barrier location on a road or engineering structure and the road and traffic conditions on their functionality and safety. The paper will present the preliminary results of this research. Once complete, the research will offer tools to help with the implementation of road restraint systems. The tools will ensure that road infrastructure is safer and that the most common mistakes are eliminated.

Performance of some basic types of road barriers subjected to the collision of a light vehicle

The investigation of the performance of road barriers to the car collision is not very often studied in the literature despite the importance of the topic to the passengers' safety. Indeed, the various road barriers systems are seldom compared in terms of their capabilities in reducing the overall damage in an accident. Here, flexible and rigid road restraint system subjected to a 900 kg car impact is studied in detail via a finite element simulation, with the model being validated against experimental results. The model relies on dynamic material properties for the guardrail, which were measured in Split Hopkinson Pressure Bar. Three severity occupant indexes, ASI, THIV and PHD, are explored and used to infer road barriers behaviour when interacting with a light vehicle. It is also investigated the failure limit of bolted connections and its influence on the guardrail impact result by means of the car trajectory. According to test TB11 from EN 1317 standard, the impact simulation results using a 900 kg car show that the flexible guardrail is safer than any of the analysed concrete barriers.

Assessment of Road Restraint Systems in Polish Conditions

Abstract Key to understanding the needs and tools of road infrastructure management is identifying the hazards and their sources involved in having no or faulty road restraint systems. Clarity is also needed on why the systems are wrongly designed, constructed, built and operated. To ensure that the problem is adequately understood, research and site observations were conducted and mathematical models were built to describe the level of roadside risk. To aid studies of road safety barrier and other road safety equipment functionality, it is vital to carry out field crash tests and crash test simulations. The main goal of the work is to develop a method for selecting optimal road restraint systems.

Evaluating the safety benefit of retrofitting motorways section with barriers meeting a new EU standard: Comparison of observational before–after methodologies

Abstract The road safety barriers are today designed and installed in compliance with the European standards for Road Restraint Systems (EN 1317), which lays down common requirements for the testing and certification in all EU countries. The introduction of the European Union (EU) regulation for safety barriers, which is based on performance, has encouraged European road agencies to perform an upgrade of the old barriers installed before 2000, with the expectation that there will be safety benefits at the retrofitted sites. Due to the high cost of such treatments, a benefit-cost analysis (BCA) is often used for site selection and ranking and to justify the investment. To this aim a crash modification factor (CMF) has to be applied and errors in the estimation of benefits are directly reflected in the reliability of BCA. Despite the benefits of empirical Bayes before–after (EB–BA) analysis or similar rigorous methods are well-known in the scientific world, these approaches are not always the standard for estimating the effectiveness of safety treatments. To this aim, the differences between the EB–BA and a naive comparison of observed crashes before and after the treatment are presented in the paper. Crash modification factors for total and target crashes are estimated by performing an EB–BA based on data from a motorway in Italy. As expected the results suggest a strong safety benefit for the ran-off-road crashes by reducing the number of severe crashes (fatal and injury). The statistical significance of results obtained by the EB–BA approach show that the retrofits are still cost-effective. The comparison pointed out as selection bias effects can overestimate the safety benefit of the retrofits when a naive approach is used to estimate the CMF and how those can significantly affect a benefit-cost analysis.