Roadside Safety Hardware Research Articles

Characterization of Motorcycle Encroachments in the U.S

In 2020, there were 5,579 motorcyclist fatalities in the U.S., which is the highest on record. Despite accounting for only 3% of registered vehicles, motorcycles are involved in 42% of fatal guardrail impacts. Roadside safety hardware testing guidelines are outlined in the Manual for Assessing Safety Hardware (MASH) for passenger vehicles and large trucks but these procedures do not include any motorcycle impacts. Although international test procedures for roadside hardware prescribe motorcycle crash tests, it is not known if the prescribed test conditions reflect the conditions at which motorcycles depart the roadway in the U.S. A better understanding of the characteristics of motorcycles departing the roadway in the U.S. is needed before the development of motorcycle crash tests. This study used the National Cooperative Highway Research Program (NCHRP) 17-88 database to compare the encroachment and impact characteristics of motorcycles, passenger vehicles, single-unit trucks, and tractor-trailer trucks. Motorcycles were found to have a similar distribution of impact angles to passenger vehicles, with an 85th percentile of 24 degrees. The median and 85th percentile impact angle was found to be shallower for tractor-trailer trucks compared with motorcycles and passenger vehicles. Additionally, large trucks and motorcycles were found to roll over at a higher frequency than passenger vehicles. During the first event, almost 80% of motorcycles were upright. By the second event, almost 50% of motorcyclists were separated from the motorcycle. This indicates that a large percentage of riders lose contact with the motorcycle during the first event and are separated during any subsequent events. Based on these results, future motorcycle-barrier tests should consider an upright configuration and an impact angle of 24 degrees.

Experimental Investigation of Axial Cutting of AA6061 Extrusions under a Tension Deformation Mode

<div class="section abstract"><div class="htmlview paragraph">A plethora of applications in the transportation industry for both vehicular and roadside safety hardware, especially seatbelts, harnesses and restraints, rely on tensile loading to dissipate energy and minimize injury. There are disadvantages to the current state-of-the-art for these tensile energy absorbers, including erratic force-displacement responses and low tensile force efficiencies (TFE). Axial cutting was extensively demonstrated by researchers at the University of Windsor to maintain a stable reaction force, although exclusively under compressive loading. A novel apparatus was investigated in this study which utilized axial cutting under a tensile loading condition to absorb energy. A parametric scope was chosen to include circular AA6061 extrusions in both T4 and T6 temper conditions with an outer diameter of 63.5 mm and wall thickness of 3.18 mm. The experiments were performed quasi-statically utilizing a custom, hydraulically powered long stroke tension/compression testing machine with a maximum capacity of 300kN. Strain-gauge based load cells and non-contact displacement transducers were implemented to measure the cutting force and displacement response of the setup. The results demonstrated highly stable force responses, with cutting force efficiencies typically in the vicinity of 90%. The experimental force-displacement responses exhibited a high degree of repeatability and correlation to the analytical model. Critical performance metrics, including the mean load and total energy absorption, were predicted to within 5 %. Additionally, the complete force-displacement response was predicted utilizing an analytical modeling approach with an average validation metric of approximately 0.92.</div></div>

Development of an 1100C Crushable Nose Surrogate Vehicle for Low-Speed Impact Testing of Breakaway Hardware

In the development of breakaway roadside safety hardware, surrogate vehicles offer an efficient, cost-effective means of testing new breakaway design concepts and evaluating system performance in accordance with applicable standards. For the purposes of conducting low-speed impact testing, a crushable nose impactor, when combined with a gravity pendulum, can constitute a suitable surrogate alternative to a production vehicle. This paper describes the development of a crushable nose impactor that can serve as a surrogate version of the 1100C passenger car described in AASHTO’s Manual for Assessing Safety Hardware. The design of the new crushable nose was based on published force–deformation data collected from crash testing of a Kia Rio production passenger car. The new crushable nose differs from other designs in that it is intended specifically for use in low-speed impact testing of breakaway hardware; the nose uses tapered (i.e., trapezoidal) aluminum honeycomb cartridges, which permits improved approximation of the production vehicle force–deformation curve; and the cartridge design process incorporates insights gained through high-deformation compression testing of aluminum honeycomb materials. This paper documents ( a) the analysis techniques that were used iteratively to design the new crushable nose and ( b) the final dimensions of the configured cartridges. The results from rigid pole validation impact testing of the crushable nose impactor, conducted with the Florida Department of Transportation’s gravity pendulum, are presented and shown to be in good agreement with the production vehicle force–deformation data.

Road side safety hardware: Current status and future outlook

As an integral part of engineering safer roads, road side safety devices passively interact with errant vehicles to redirect them safely back to the road or bring them to a safe and controlled stop. These devices take the form of crash cushions, cable barriers, concrete barriers, steel barriers, guard rails, guardrail terminals and others. Placement criteria and warrants are established in the AASHTO Road Side Design Guide (1). However, before those devices are placed on the roadways, they have to be evaluated under objective test conditions.. Given that possible combinations of impact speeds, impact angles, vehicle characteristics and roadway characteristics are infinite, it is impossible to design roadside safety hardware for all those combination. Thus a “Practical Worse Case” philosophy derived from crash data analyses is followed to determine such impact conditions. In the USA, the evaluation methodologies are established in the National Cooperative Highway Research Program (NCHRP) Report 350 (2) which is now superseded by Manual for Assessing Safety Hardware (MASH) guidelines (3). In Europe a comparable set of guideline (EN 1317) is used to evaluate road safety devices under vehicular impact. Many roadway authorities around the world adopt either EN 1317 or NCHRP Report 350 with some modifications to incorporate local requirements. In the early parts of this presentation demonstrate testing conditions and criteria for quantifying the device as crashworthy under NCHRP Report 350 and MASH for some of the common road safety devices. The most common test conditions are explained in details. The key criteria of acceptance shall be presented for the most common test conditions. State of the art nonlinear finite element methodology has been gaining tractions in designing and enhancing the safety of vehicles and roadside devices. This presentation will highlight roadside safety hardware (4, 5, and 6) that was designed through extensive simulation process and had subsequent successful crash test per the latest MASH guidelines. REFERENCES 1. America Association of State Highway and Transportation Officials , Roadside Design Guide, 4th Edition, AASHTO, 2011. 2. Ross, H.E., D.L. Sicking, R.A. Zimmer, and J.D. Michie, Recommended Procedures for the Evaluation of Highway Features, NCHRP Report No. 350, 1993, Transportation Research Board: Washington, D.C. 3. AASHTO, Manual for Assessing Safety Hardware, 2009, American Association of State Highway and Transportation Officials: Washington, D.C. 4. Abu-Odeh, K.M. McCaskey, R.P. Bligh, W.L. Menges, D.L. Kuhn. Crash Test and MASH TL-3 Evaluation of the TxDOT Short Radius Guardrail. Test Report. 0-6711-1. Project No. 0-6711. Texas A&M Transportation Institute, College Station, TX. March 2015 5. A. Abu-Odeh, R.P. Bligh, M.L. Mason, W.L. Menges. Development and Evaluation of a MASH TL-3 31-Inch W-Beam Median Barrier. 9-1002-12-8. Texas A&M Transportation Institute, College Station, TX. January 2014. 6. A. Abu-Odeh, W.F. Williams, M. Ferdous, M.T. Spencer, R.P. Bligh, W.L. Menges. Safety and Integrity of Median Barrier-Mounted Hardware. 0-6646-S. Texas A&M Transportation Institute, College Station, TX. 2013.

Injury Outcome in Crashes with Guardrail End Terminals

Objective: The goal of this study is to evaluate the crash performance of guardrail end terminals in real-world crashes. Guardrail end terminals are installed at the ends of guardrail systems to prevent the rail from spearing through the car in an end-on collision. Recently, there has been a great deal of controversy as to the safety of certain widely used end terminal designs, partly because there is surprisingly little real-world crash data for end terminals. Most existing studies of end terminal crashes used data from prior to the mid-1990s. Since then, there have been large improvements to vehicle crashworthiness and seat belt usage rates, as well as new roadside safety hardware compliant with National Cooperative Highway Research Program (NCHRP) Report 350, “Recommended Procedures for the Safety Performance Evaluation of Highway Features.” Additionally, most existing studies of injury in end terminal crashes do not account for factors such as the occurrence of rollover. This analysis uses more recent crash data that represent post-1990s vehicle fleet changes and account for a number of factors that may affect driver injury outcome and rollover occurrence.Methods: Passenger vehicle crashes coded as involving guardrail end terminals were identified in the set of police-reported crashes in Michigan in 2011 and 2012. End terminal performance was expected to be a function of end terminal system design. State crash databases generally do not identify specific end terminal systems. In this study, the coded crash location was used to obtain photographs of the crash site prior to the crash from Google Street View. These site photographs were manually inspected to identify the particular end terminal system involved in the crash. Multiple logistic regression was used to test for significant differences in the odds of driver injury and rollover between different terminal types while accounting for other factors.Results: A total of 1,001 end terminal crashes from the 2011–2012 Michigan State crash data were manually inspected to identify the terminal that had been struck. Four hundred fifty-one crashes were found to be suitable for analysis. Serious to fatal driver injury occurred in 3.8% of end terminal crashes, moderate to fatal driver injury occurred in 11.8%, and 72.3% involved property damage only. No significant difference in moderate to fatal driver injury odds was observed between NCHRP 350 compliant end terminals and noncompliant terminals. Car drivers showed odds of moderate to fatal injury 3.6 times greater than LTV drivers in end terminal crashes. Rollover occurrence was not significantly associated with end terminal type.Conclusions: Car drivers have greater potential for injury in end terminal crashes than light truck/van/sport utility vehicle drivers. End terminal designs compliant with NCHRP 350 did not appear to carry different odds of moderate driver injury than noncompliant end terminals. The findings account for driver seat belt use, rollover occurrence, terminal orientation (leading/trailing), control loss, and the number of impact events. Rollover and nonuse of seat belts carried much larger increases in injury potential than end terminal type. Rollover did not appear to be associated with NCHRP 350 compliance.

Worst-Case Connection Strength Considerations in Designing Certification Crash Test Experiments for W-Beam Guardrail

Certification crash test experiments conducted in controlled laboratory environments play a crucial role in the product development cycle of roadside safety hardware by linking analysis, design, and real-world in-service performance along low-volume roads (LVRs). The AASHTO Manual for Assessing Safety Hardware worst-case testing philosophy prescribes a commonsense approach to ensuring reliable real-world performance in designing certification crash test experiments for W-beam guardrails. Literature of the past two decades establishes extreme rail-to-post connection strength variability as a component-level trigger mechanism of guardrail system-level failure modes that degrade the reliability of guardrail safety performance. A range of primary and secondary release mechanisms with their associated variability sources is examined from the perspective of characterizing the worst case for each release mechanism. A case is made to support a recommendation that worst-case connection strength be systematically represented in designing certification crash test experiment matrices that are intended to ensure adequate performance of guardrails along LVRs. A systematic general methodology is introduced for defining compounded worst-case connection strength. The standard button head mounting bolt of the modified G4(1S) and Midwest Guardrail System family is considered as an example. Detailed evaluation of variability extremes in button head bolt connection strength indicates that optimizing the existing button head bolt release mechanism is not possible, even with the use of mid-span splices. Thus, it is recommended that an optimized release mechanism solution—such as the Gregory Mini Spacer guardrail fastener—be considered, consistent with the award-winning science of release for guardrail optimization to improve roadside safety along LVRs and other roadways in the United States, Europe, and developing countries.

Safety Performance of G4 (1S) W-Beam Guardrails versus Cable Median Barriers on Florida's Freeways

Different roadside safety hardware including guardrails and cable barriers have been installed on freeways to prevent run-off-the-road and median crossover crashes. This article compares the safety performance of G4 (1S) strong-post W-beam guardrails and cable barriers installed in the medians on freeways in Florida. The comparison is based on the percentages of barrier and median crossovers by vehicle type and crash severity. A crash is categorized as barrier crossover crash if the errant vehicle crosses the barrier during the crash. If after crossing the barrier the errant vehicle clears the median and traverses into the opposite travel lanes, it becomes a median crossover crash. To obtain a more precise measurement of barrier performance, this study considers only crashes involving vehicles hitting a barrier. A total of 678.9 miles of freeways with G4 (1S) W-beam guardrails and 101.0 miles of freeways with cable barriers were identified. Police reports of 8,536 crashes from years 2006 to 2010 at these locations were reviewed. Z-test and odds ratio were used to compare the safety performance of cable median barriers and guardrails. Overall, guardrails performed slightly better than cable barriers in terms of barrier and median crossover crashes. However, cable median barriers were found to result in fewer severe injury crashes.

Performance of the Midwest Guardrail System with Rectangular Wood Posts

Strong-post W-beam is one of the most enduring and prolific safety barriers in the world. Over the years, it has been modified and updated to improve performance. Throughout these changes, two types of guardrail posts have been used to support the rail element: W6 × 8.5 steel posts and 6-in.-wide × 8-in.-deep wood posts. Recent updates to roadside safety hardware evaluation criteria and concerns with the performance of the G4 (1S) and G4 (2W) strong-post W-beam systems have led to the need for enhanced strong-post guardrail designs. The Midwest Guardrail System (MGS) was developed to address this need and provides improved performance over previous strong-post W-beam systems. The MGS was developed and tested with steel support posts, and it was believed that the use of wood posts in the system would provide similar barrier performance. However, the effect of wood posts in the MGS was never quantified through full-scale crash testing. The objective of this study was to investigate and evaluate the performance of the MGS with rectangular posts made of southern yellow pine. This effort included a review of the performance of wood and steel guardrail posts as it pertained to the MGS, the completion of two full-scale crash tests according to the Manual for Assessing Safety Hardware (MASH) safety requirements, and a comparison of the full-scale test results with MASH safety criteria and previous steel-post and alternative species wood-post MGS tests. Finally, recommendations were developed to implement the wood-post MGS and wood posts in MGS special applications.

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.

Collision behaviour of double W-beam transition

Vehicle collisions result in many injuries and fatalities every year all around the world. A significant number of those incidents occur outside the roadway, partly owing to the incompatibility between the roadside safety hardware and impacting vehicles. Although the purpose of using roadside safety hardware is safely to contain impacting vehicles and reduce impact severity, use of inadequate safety hardware can have serious consequences. In this study, the crash behaviour of a currently used double W-beam transition barrier was analysed and its adequacy is evaluated using a series of five vehicular impacts. Finite element simulations were used to perform the analysis, and a full-scale crash test result was used to validate the finite element models used in the study. Results of the analysis predict that double W-beam transition can safely contain and redirect vehicles ranging from compact automobiles to high centre of gravity heavy trucks up to 10,000 kg in mass. Occupant injury risk values obtained from all five cases are also calculated and presented. Further use of computational tools in safety evaluation of the existing roadside safety hardware is strongly recommended.

Termination and Anchorage of Temporary Concrete Barrier

The research study described herein developed an economical method for terminating and anchoring the upstream end of temporary concrete barrier systems. The termination and anchorage system was designed for use with the Kansas F-shape temporary concrete barrier design that is currently used by several states participating in the Midwest Pooled Fund Program. These efforts were performed in accordance with the Test Level 3 guidelines found in the Manual for Assessing Safety Hardware 2008. Criteria governing the design of the termination and anchorage system included development of adequate anchor loads over a finite deflection in order to limit peak loads, mitigation of vertical rotation and tipping of the end barrier about its longitudinal axis, and employing existing roadside safety hardware in the design to limit state hardware inventories. The termination and anchorage system allowed for a significant reduction in the number of barrier segments required upstream from the length of need and for use in anchoring a free-standing TCB system. The anchorage system was configured to effectively constrain the end of the TCB system for impacts as far upstream as the first anchored barrier segment. Full-scale crash testing demonstrated that the impacting vehicle was safely and smoothly redirected, and the test was judged acceptable according to the Test Level 3 safety criteria set forth in the Manual for Assessing Safety Hardware 2008.

Effect of permanent jersey-shaped concrete barrier height on heavy vehicle post-impact stability

Jersey-shaped permanent concrete barriers are extensively used at narrow medians, bridge decks and at roadsides where lateral barrier deformations are not allowed. It is well documented that the crash performance of concrete barriers depends mainly on the barrier geometry, such as shape and top height. In most US applications, the height of jersey-shaped concrete barriers is 810 mm, whereas in Europe, concrete barriers as tall as 1000 mm are used. According to European EN1317 crash test guidelines, concrete barriers should demonstrate acceptable crash test performances against 10, 30 and 38 ton heavy vehicle impacts. In this paper, the effect of permanent jersey-shaped concrete barrier height on post-impact stability of 10 and 30 ton heavy vehicles is investigated. A versatile finite element program LS-DYNA capable of representing crash test behaviour of roadside safety hardware is used for the analysis. A total of five simulations, four with a 30 ton vehicle and one with a 10 ton vehicle, are performed. Permanent jersey-shaped barriers with 810, 950, 1000 and 1050 mm top heights are modelled and subjected to 30 ton vehicle impact. Only one simulation is performed on 810 mm tall barrier using 10 ton vehicle. Simulation results predict that a minimum of 1050 mm concrete barrier height is necessary to achieve post-impact stability for the 30 ton vehicle. For the 10 ton vehicle, a conventional 810 mm tall barrier is found to be adequate to provide stable vehicle redirection. As always, full-scale crash testing is recommended to verify the acceptability of simulation findings.

Comparison of roadside and vehicle crash test injury criteria in frontal crash tests

The flail space model is widely used to assess occupant injury risk potential in full-scale crash tests of roadside safety hardware, e.g. guardrail. A fundamental assumption of this model is that the occupant is unbelted and not airbag restrained. In the early 1980s, these were valid assumptions in the US: cars were not airbag equipped and belt usage rates were around 11%. In today's US vehicle fleet, however, these assumptions are questionable: the belt usage rate is approximately 80% and airbags are required equipment. These changes have significant implications on injury risk computed using the original flail space model. The objective of this study is to contrast flail space model injury risk with the widely accepted dummy-based injury criteria in frontal crashes involving unbelted, belted or airbag restrained occupants. In an analysis of 39 frontal crash tests of speeds ranging from 40 to 97 km/hr, the flail space model was unable to account for variations in occupant risk due to the presence and per...

Comparison of roadside crash injury metrics using event data recorders

The occupant impact velocity (OIV) and acceleration severity index (ASI) are competing measures of crash severity used to assess occupant injury risk in full-scale crash tests involving roadside safety hardware, e.g. guardrail. Delta-V, or the maximum change in vehicle velocity, is the traditional metric of crash severity for real world crashes. This study compares the ability of the OIV, ASI, and delta-V to discriminate between serious and non-serious occupant injury in real world frontal collisions. Vehicle kinematics data from event data recorders (EDRs) were matched with detailed occupant injury information for 180 real world crashes. Cumulative probability of injury risk curves were generated using binary logistic regression for belted and unbelted data subsets. By comparing the available fit statistics and performing a separate ROC curve analysis, the more computationally intensive OIV and ASI were found to offer no significant predictive advantage over the simpler delta-V.

Validation of a Single Unit Truck model for roadside hardware impact

The objective of this research is to validate the Finite Element (FE) model of a Ford F800 Single Unit Truck (SUT). The FE model of the SUT was developed at the FHWA/NHTSA National Crash Analysis Centre (NCAC) at the George Washington University (GWU). In this study, the characteristics of the SUT model were investigated and several modifications were incorporated in the model to accurately simulate its interaction with roadside safety hardware. A full-scale crash test of the Ford F800 SUT impacting an F-shape Portable Concrete Barrier (PCB) was conducted at The Federal HighWay Administration's (FHWA) Federal Outdoor Impact Laboratory (FOIL) and used in the validation. The response of any vehicle impacting a PCB is primarily governed by the mass and suspension characteristics of the vehicle. Detailed methods for modelling the truck's suspension components are discussed.

Development of a 30,000 kg heavy goods vehicle for LS-DYNA applications

In this paper, a finite element model of a 30,000 kg Heavy Goods Vehicle (HGV) was developed and validated against full-scale crash test data. Since this vehicle is a standard test vehicle in the European crash test standards, EN1317, development of an accurate vehicle model was deemed to be a positive contribution to the evaluation of roadside safety hardware. The vehicle model reproduces a FIAT-IVECO F180 truck, a vehicle with four axles and a mass of 30,000 kg when fully loaded. The model consisted of 12,337 elements and 11,470 nodes and was built for and is ready to use with LS-DYNA finite element code from Livermore Software Technology Corporation. Data available from two previously performed full-scale crash tests, one on a steel bridge rail and the other on a portable concrete barrier, were used to validate the accuracy of the HGV model. Results of the finite element simulation study show that the developed HGV model shows promise and can accurately replicate the behaviour of an actual HGV in a full-scale crash test. Improvements such as the steering mechanism in the front axles and the suspension system are currently underway to make the model more realistic.

Evaluation of Threshold Values of Acceleration Severity Index by Using Event Data Recorder Technology

The acceleration severity index (ASI) is used to evaluate the potential for occupant risk in full-scale crash tests involving roadside safety hardware. Despite the widespread use of the index across Europe, there is a lack of research relating this metric to occupant injury in real-world collisions. Recent installation of event data recorders (EDRs) in a number of late-model vehicles presents a different perspective on the assessment of the validity of occupant risk based on the ASI. EDRs are capable of electronically recording data such as vehicle speed, brake status, and throttle position just before and during an accident. Of particular interest is the EDR's ability to document the deceleration of a vehicle during a collision event. This research used EDR technology to investigate the correlation between the ASI threshold limits and the potential for occupant injury in crash events. The longitudinal ASI was found to be a good predictor of overall injury, and the intent of the current preferred threshold value of 1.0 appears valid. Limitations include investigation of the longitudinal direction only, lack of injuries on the abbreviated injury scale (AIS) in excess of AIS 3, and no control for occupant compartment intrusion.

Evaluation of Threshold Values of Acceleration Severity Index by Using Event Data Recorder Technology

The acceleration severity index (ASI) is used to evaluate the potential for occupant risk in full-scale crash tests involving roadside safety hardware. Despite the widespread use of the index across Europe, there is a lack of research relating this metric to occupant injury in real-world collisions. Recent installation of event data recorders (EDRs) in a number of late-model vehicles presents a different perspective on the assessment of the validity of occupant risk based on the ASI. EDRs are capable of electronically recording data such as vehicle speed, brake status, and throttle position just before and during an accident. Of particular interest is the EDR's ability to document the deceleration of a vehicle during a collision event. This research used EDR technology to investigate the correlation between the ASI threshold limits and the potential for occupant injury in crash events. The longitudinal ASI was found to be a good predictor of overall injury, and the intent of the current preferred threshol...

LS-DYNA Simulation Influence on Roadside Hardware

Several new roadside safety appurtenances that can be directly linked to the use of nonlinear finite element analysis with LS-DYNA are being installed along the nation's roadways. These advances can be attributed to FHWA's sponsored research program known as Centers of Excellence in DYNA3D Analysis. Some of the simulation efforts at the Midwest Roadside Safety Facility over the past 10 years are documented to help educate the roadside safety engineer and to promote the use of simulation. Noteworthy progress has been made in the use of LS-DYNA for the design and analysis of roadside safety hardware, and it is believed that a great deal more progress is possible.

Tests and simulation of a w-beam rail-to-post connection

The bolted connection of a w-beam rail to a guardrail post can have a significant affect on the performance of a guardrail system. For example, if the connections are too strong, the w-beam is likely to be pulled to the ground with the post and result in the vehicle overriding the guardrail. If the connections are too weak, the rail can pull away from the posts too soon allowing the rail to drop and the vehicle to penetrate behind the system. In recent years, finite element simulation has rapidly become a fundamental part of the analysis and design of roadside safety hardware systems, and as such, the finite element models must be capable of accurately simulating the response of these bolted connections. One of the challenges of simulating guardrail collisions is obtaining accurate models of each of the distinct components of the system, such as the various types of bolted connections, and properly modelling their interaction with each other. This study investigates the failure mechanism of the bolted connection of a w-beam rail to a guardrail post using laboratory experiments and uses that information to develop computationally efficient and accurate finite element models of the rail-to-post connection that can be used in routine analysis of guardrail system performance using LS-DYNA.