Safety Hardware Research Articles

Incorporating Traffic Control and Safety Hardware Performance Functions into Risk-based Highway Safety Analysis

Traffic control and safety hardware such as traffic signs, lighting, signals, pavement markings, guardrails, barriers, and crash cushions form an important and inseparable part of highway infrastructure affecting safety performance. Significant progress has been made in recent decades to develop safety performance functions and crash modification factors for site-specific crash predictions. However, the existing models and methods lack rigorous treatments of safety impacts of time-deteriorating conditions of traffic control and safety hardware. This study introduces a refined method for computing the Safety Index (SI) as a means of crash predictions for a highway segment that incorporates traffic control and safety hardware performance functions into the analysis. The proposed method is applied in a computation experiment using five-year data on nearly two hundred rural and urban highway segments. The root-mean square error (RMSE), Chi-square, Spearman’s rank correlation, and Mann-Whitney U tests are employed for validation.

A methodology for the analysis of domino and cascading events in Oil & Gas facilities operating in harsh environments

The present study is aimed at defining a structured approach to the quantitative assessment of cascading events triggered by fire, accounting for the influence of harsh environmental conditions on the emergency response and on the performance of hardware safety barriers. A specific metric was defined in order to consider the external factors related to harsh environments on the determination of hardware and emergency safety barriers availability, with a specific focus on operations in extremely cold climates. The metric allows evaluating the time scale of emergency and the related efficiency of barriers in contrasting accident escalation. The values obtained for availability and effectiveness of barriers were input to a specific event tree analysis in order to support the quantitative assessment of accident frequency associated to cascading events. The approach is tested by its application to a case study, aimed at the assessment of the influence of extremely cold environmental conditions on the risk due to cascading events in an industrial site.

Development of a Test Level 3 Transition Between Guardrail and Portable Concrete Barriers

Road construction often requires that work zones be created and shielded by portable concrete barriers (PCBs) to protect workers and equipment from errant vehicles as well as to prevent motorists from striking other roadside hazards. For an existing W-beam guardrail system installed adjacent to the roadway and near the work zone, guardrail sections are removed so a PCB system can be placed. A study was done to develop a crashworthy transition between W-beam guardrail and PCB systems. Design concepts were developed and refined through computer simulation with LS-DYNA. Additionally, a study of critical impact points was conducted to determine impact locations for full-scale crash testing. The design effort resulted in a new system consisting of a Midwest Guardrail System that overlapped a series of F-shape PCB segments placed at a 15:1 flare. In the overlapped region of the barrier systems, uniquely designed blockout supports and a specialized W-beam end shoe mounting bracket were used to connect the systems. Three full-scale vehicle crash tests were successfully conducted according to the Manual for Assessing Safety Hardware Test Level 3 safety performance criteria. Because of the successful test results, a Test Level 3 crashworthy guardrail-to-PCB transition system is now available for protecting motorists, workers, and equipment in work zones.

Development and Testing of the Manitoba Constrained Width Tall Wall Barrier

This project in Manitoba, Canada, developed a single-slope concrete barrier system with a height of 1,250 mm and a base width of no more than 600 mm. Configurations for bridge rail, roadside, and median barrier applications were developed and optimized to minimize installation costs while satisfying the AASHTO Manual for Assessing Safety Hardware (MASH) Test Level 5 performance standards. Additionally, a bridge deck was developed for the overhang portion of the deck supporting the bridge rail. To evaluate the new barrier system, a 45.7-m-long section of the bridge rail was constructed on a simulated bridge deck and subjected to a full-scale crash test according to MASH Test 5-12. During the test, the 36,000-kg vehicle was safely redirected with minimal roll to the cab and trailer. Damage to the barrier and deck was minor, consisting of concrete gouging, hairline cracks, and some spalling to the top of the barrier. Thus, the Manitoba constrained width tall wall was deemed crashworthy to MASH Test Level 5 standards.

Standard Midwest Guardrail System Placed at 1V:2H Slope Break Point or with Omitted Post

State departments of transportation (DOTs) throughout the United States commonly use W-beam guardrail systems to keep errant vehicles from leaving high-speed roadways and encountering safety hazards adjacent to the roadway edge, such as steep roadside slopes. Additionally, although W-beam guardrail is used to protect errant vehicles from safety hazards along the roadways, obstructions at post locations within a run of guardrail are a common occurrence. State DOTs wanted to evaluate the standard Midwest Guardrail System (MGS) for use in these instances. First, the standard MGS with 6-ft (1,829-mm) W6 × 8.5 (W152 × 12.6) steel posts spaced at 75 in. (1,905 mm) placed at the slope break point of a 1V:2H slope was successfully crash tested and evaluated according to the Test Level 3 (TL-3) safety performance criteria presented in the Manual for Assessing Safety Hardware (MASH). Subsequently, the standard MGS with one omitted post, which created an unsupported span of 12.5 ft (3.8 m), was full-scale crash tested, and it satisfied the MASH TL-3 safety performance criteria. Because multiple variations of the MGS system have been developed for special applications, recommendations for the omission of a post or installation on a steep slope will vary depending on the nature and behavior of the application. The safety performance of various MGS configurations and special applications was compared. Implementation guidance was then given about the use of the MGS placed at the slope break point and omitting a post in the MGS with MGS special applications. These special applications included terminals and anchorages, MGS stiffness transition to thrie beam approach guardrail transitions, MGS long-span system, MGS adjacent to 1V:2H fill slopes, MGS on 1V:8H approach slopes, MGS in combination with curbs, wood post MGS, and MGS without blockouts.

Using field feedback to estimate failure rates of safety-related systems

The IEC 61508 and IEC 61511 functional safety standards encourage the use of field feedback to estimate the failure rates of safety-related systems, which is preferred than generic data. In some cases (if “Route 2H” is adopted for the "hardware safety integrity constraints”), this is even a requirement. This paper presents how to estimate the failure rates from field feedback with confidence intervals, depending if the failures are detected on-line (called "detected failures", e.g. by automatic diagnostic tests) or only revealed by proof tests (called "undetected failures"). Examples show that for the same duration and number of failures observed, the estimated failure rates are basically higher for “undetected failures” because, in this case, the duration observed includes intervals of time where it is unknown that the elements have failed. This points out the need of using a proper approach for failure rates estimation, especially for failures that are not detected on-line. Then, this paper proposes an approach to use the estimated failure rates, with their uncertainties, for PFDavg and PFH assessment with upper confidence bounds, in accordance with IEC 61508 and IEC 61511 requirements. Examples finally show that the highest SIL that can be claimed for a safety function can be limited by the 90% upper confidence bound of PFDavg or PFH. The requirements of the IEC 61508 and IEC 61511 relating to the data collection and analysis should therefore be properly considered for the study of all safety-related systems.

Crashworthiness of G4(2W) guardrail system: a finite element parametric study

ABSTRACTIn recent years, vehicle demographics have changed to include a relatively large proportion of light trucks, such as pickups, vans and sport-utility vehicles. It is found that several types of guardrail systems, including the G4(2W) guardrail system, are unable to redirect the pickup trucks to roadway safely. Therefore, in this study, several options are considered; they include improving the splice connections and adjusting the guardrail height and the post spacing to improve the performance of this system. The G4(2W) guardrail system is modelled in LS-DYNA and validated with a previous full-scale crash test conducted by the Texas A&M Transportation Institute. A parametric study based on the results of the LS-DYNA crash simulation according to Length of Need test 3-11 and 3-10 is conducted to investigate key factors of guardrail systems, including the splice configuration, the post spacing and the guardrail height. The purpose of this study is to find a model that satisfies the requirements of Test Level 3 outlined in Manual for Assessing Safety Hardware (MASH)'s criteria.

Development and validation of a finite element model for road safety barrier impact tests

Road safety barriers are roadside structures installed on certain sections of the road to improve highway safety by preventing a vehicle from leaving the road and colliding with roadside hazards. Road safety barriers are an effective solution for reducing the risk of injuries on modern roads. A road safety barrier must meet minimum standards of construction and materials design. Normally, they must undergo crash tests according to the European standard EN 1317 or the Manual for Assessing Safety Hardware by the American Association of State Highway and Transportation Officials. On the basis of these standards, each safety barrier must pass standardized crash tests as mandated in their approval procedures. Currently, computer simulation methods are typically used by researchers to analyze the performance of roadside safety barriers. Advancement in computer technology could facilitate the finite element method in replacing expensive experimental tests. This paper presents an approach for constructing and evaluating a finite element model for road safety barriers according to European standard EN 1317 by using the finite element code LS-DYNA. Excellent agreement between real-world test data and simulation results was achieved for behavior and impact severity values. The results obtained using the model ensure the exactness of the proposed method and prove that the numerical method is a practical approach for eliminating road safety barrier problems. Furthermore, the model was able to replace experimental tests for developing road safety barriers, thus reducing time and money.

Evaluation of the Midwest Guardrail System stiffness transition with curb

ABSTRACTA W-beam to thrie beam stiffness transition with a 102-mm (4-in.) tall concrete curb was developed to connect 787-mm (31-in.) tall W-beam guardrail, commonly known as the Midwest Guardrail System (MGS), to a previously developed thrie beam approach guardrail transition system. This upstream stiffness transition was configured with standard steel posts that are commonly used by several state departments of transportation. The toe of a 102-mm (4-in.) tall sloped concrete curb was placed flush with the backside face of the guardrail and extended the length of the transition region. Three full-scale crash tests were conducted according to the Test Level 3 (TL-3) safety standards provided in AASHTO's Manual for Assessing Safety Hardware (MASH). The first test, MASH Test No. 3-20, was deemed a failure due to guardrail rupture. The stiffness transition was modified to include an additional nested W-beam rail segment upstream from the W-beam to thrie beam transition element. MASH Test No. 3-20 was repeated on the modified system, and the 1100C small car was successfully contained and redirected. During MASH Test No. 3-21, a 2270P pickup truck was successfully contained and redirected. Following the crash testing program, the system was deemed acceptable according to the TL-3 safety performance criteria specified in MASH.

Design optimization of a MASH TL-3 concrete barrier using RBF-based metamodels and nonlinear finite element simulations

Concrete barriers are one of the most widely used safety features for preventing errant vehicles from entering opposing travel lanes on highways. As a safety device, a concrete barrier is also required to safely redirect a striking vehicle such that it is not bounced into travel lanes and collide with other vehicles. Given its rigidity compared to most vehicular structures, the performance of a concrete barrier is mainly influenced by its shape or the cross-sectional geometry. Over the years, concrete barriers have been continuously improved using roadway crash data and crash tests. Although the current in-service concrete barriers satisfy the requirements of safety standards, the empirical approach is not cost-effective for designing new barrier systems. In this study, a simulation-based optimization approach was adopted to obtain the optimum design of a concrete barrier by combining nonlinear finite element (FE) simulations, metamodeling with radial basis functions (RBFs), and a genetic algorithm (GA). The performance of the concrete barrier was determined by evaluating vehicular responses specified in the current safety standard, Manual for Assessing Safety Hardware (MASH). Nonlinear FE simulations were first carried out on sample designs to obtain the vehicular responses for creating the RBF metamodels, which were then used in the optimization process to replace the expensive FE simulations. An optimal design of the concrete barrier was obtained by the GA and was shown to have improved safety performance over the original design.

Procedure for assessing hardware safety integrity in legacy systems

Functional safety is related to the safety functions of a safety-related system that uses electrical/electronic/programmable (E/E/PE) devices such as sensors, logic solvers, and final elements. A legacy system is a safety-related system which offers safety functions but which was not designed to comply with the IEC 61508 standard. This paper presents a procedure for assessing the hardware safety integrity of a legacy system so as to confirm its functional safety. The procedure defines the systematic relationship between the safety function and hardware system using a function-structure map (FSM) and assesses the hardware safety integrity centered on the safety function. The proposed procedure is applied to a boiler control system of a fossil-fuel power plant.

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.

Manual for Assessing Safety Hardware Test Level 4 Design and Evaluation of a Restorable Energy-Absorbing Concrete Barrier

A new, high-containment longitudinal barrier was designed to reduce the acceleration imparted to passenger vehicles during impacts and to be restorable and reusable. Elastomer support posts were designed to translate laterally and absorb energy when struck and then to restore to their initial position after impact events. A hybrid concrete beam and steel tube combination rail was optimized to minimize weight, provide sufficient structural capacity, maintain a height to contain and redirect single-unit trucks, and prevent passenger vehicles from snagging on the posts. Three full-scale vehicle crash tests were conducted according to the Manual for Assessing Safety Hardware ( MASH) Test Level 4 (TL-4) safety performance requirements on a barrier 240 ft long with nominal height of 38⅝ in. In the Safer for Highway Test 1 (SFH-1), a 5,021-lb pickup truck was redirected with minimal damage to the barrier. The peak lateral acceleration was reduced 47% compared with similar impacts on rigid barriers. In the SFH-2 test, a 2,406-lb small car was redirected by the barrier, and the peak lateral acceleration was reduced 21%compared with similar impacts on rigid barriers. In the SFH-3 test, a 21,746-lb single-unit truck was successfully contained and redirected, resulting in only minor damage to the concrete rail. Therefore, the barrier met all the MASH TL-4 safety performance criteria. The paper provides recommendations about the performance, future design refinements, and installation requirements of the barrier.

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.

Evaluation of Vehicle-Based Crash Severity Metrics

Objective: Vehicle change in velocity (delta-v) is a widely used crash severity metric used to estimate occupant injury risk. Despite its widespread use, delta-v has several limitations. Of most concern, delta-v is a vehicle-based metric which does not consider the crash pulse or the performance of occupant restraints, e.g. seatbelts and airbags. Such criticisms have prompted the search for alternative impact severity metrics based upon vehicle kinematics. The purpose of this study was to assess the ability of the occupant impact velocity (OIV), acceleration severity index (ASI), vehicle pulse index (VPI), and maximum delta-v (delta-v) to predict serious injury in real world crashes.Methods: The study was based on the analysis of event data recorders (EDRs) downloaded from the National Automotive Sampling System / Crashworthiness Data System (NASS-CDS) 2000–2013 cases. All vehicles in the sample were GM passenger cars and light trucks involved in a frontal collision. Rollover crashes were excluded. Vehicles were restricted to single-event crashes that caused an airbag deployment. All EDR data were checked for a successful, completed recording of the event and that the crash pulse was complete. The maximum abbreviated injury scale (MAIS) was used to describe occupant injury outcome. Drivers were categorized into either non-seriously injured group (MAIS2−) or seriously injured group (MAIS3+), based on the severity of any injuries to the thorax, abdomen, and spine. ASI and OIV were calculated according to the Manual for Assessing Safety Hardware. VPI was calculated according to ISO/TR 12353-3, with vehicle-specific parameters determined from U.S. New Car Assessment Program crash tests. Using binary logistic regression, the cumulative probability of injury risk was determined for each metric and assessed for statistical significance, goodness-of-fit, and prediction accuracy.Results: The dataset included 102,744 vehicles. A Wald chi-square test showed each vehicle-based crash severity metric estimate to be a significant predictor in the model (p < 0.05). For the belted drivers, both OIV and VPI were significantly better predictors of serious injury than delta-v (p < 0.05). For the unbelted drivers, there was no statistically significant difference between delta-v, OIV, VPI, and ASI.Conclusions: The broad findings of this study suggest it is feasible to improve injury prediction if we consider adding restraint performance to classic measures, e.g. delta-v. Applications, such as advanced automatic crash notification, should consider the use of different metrics for belted versus unbelted occupants.

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.

Minimum Effective Length for the Midwest Guardrail System

The recommended minimum length for the standard Midwest Guardrail System (MGS) is 175 ft (55.3 m) based on crash testing according to NCHRP Report 350 and AASHTO's Manual for Assessing Safety Hardware (MASH) specifications. However, varying roadside hazards and roadway geometries may require a W-beam guardrail system to be shorter than the currently tested minimum length. The effects of reducing system length for the MGS were therefore investigated. The research study included one full-scale crash test with a Dodge Ram pickup truck striking a 75-ft (22.9-m) long MGS system. The barrier system satisfied all MASH Test Level 3 (TL-3) evaluation criteria for Test Designation Number 3-11. Test results confirmed that the reduced system length did not adversely affect overall system performance or deflections. Simulations that used BARRIER VII and LS-DYNA were also conducted to analyze system performance with reduced lengths of 50 ft (15.2 m) and 62 ft 6 in. (19.1 m). Both system lengths exhibited the potential for successfully redirecting an errant vehicle at MASH TL-3 test conditions. However, these reduced-length systems would have a narrow window for redirecting vehicles and would be able to shield hazards of only a limited size. Owing to limitations associated with the computer simulations, full-scale crash testing is recommended before these shorter systems are installed.

Design and Full-Scale Testing of Low-Cost Texas Department of Transportation Type T631 Bridge Rail for MASH Test Level 2 and 3 Applications

The purpose of this project was to design and test a low-cost bridge rail system that would be compatible with the Midwest Guardrail System (31 in. height) and minimized or eliminated deck damage when impacted by errant vehicles. The Texas Type T631 bridge rail developed for this project is a flexible, low-cost bridge rail system for Test Level 2 (TL-2) applications. The Texas Department of Transportation Type T631 bridge rail designed and developed for this project was evaluated under Manual for Assessing Safety Hardware (MASH) TL-2 in 2013. The bridge rail incorporated S3X5.7 steel sections designed to yield at the post baseplate. The post baseplate was designed to distribute the baseplate bearing and shear forces without causing damage to the 8-in.-thick reinforced concrete deck. The welds on the posts were designed such that the post yielded without tearing away from the top of the baseplate. The rail element consisted of a 12-gauge W-beam rail element. The rail element was attached to the post with a bolt of diameter 5/16 in. This bolt was designed to break away without adversely affecting vehicle performance. The posts were spaced 6 ft 3 in. on centers for TL-2. The post spacing was reduced to 3 ft 1½ in. on centers and evaluated for MASH Test Level 3 (TL-3) specifications in 2014. At the smaller post spacing, the T631 met all the performance requirements of MASH TL-3. Details of the design and testing of the T631 for MASH TL-2 and MASH TL-3 specifications are provided in this paper.

The applications of SFTA and SFMEA approaches during software development process: an analytical review

Software fault tree analysis SFTA and software failure modes and effects analysis SFMEA are two well known recommended approaches for the analysis of software induced hazards in the system and are adapted in the software domain by employing the concepts of standard hardware safety approaches namely fault tree analysis FTA and failure modes and effects analysis FMEA respectively. Both SFTA and SFMEA approaches, since their inception in the software domain, have been explored, either individually or jointly, by researchers at different stages of software development. This paper presents the critical review of the published work about the applications of both these approaches in three phases, namely requirements analysis, design and implementation/coding phases of software life cycle. After presenting the analytical review, the paper identifies the problems that are currently faced during the applications of these approaches and guides the directions for carrying out further research.