Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance (2022)

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3   Introduction NCHRP Report 350 contains information for evaluating the safety performance of roadside features, such as longitudinal barriers, terminals, crash cushions, and breakaway structures (1). This document was published in 1993 and was formally adopted as the national standard by the FHWA later that year, with an implementation date for late 1998. An update to NCHRP Report 350 was developed under NCHRP Project 22-14(02), “Improved Procedures for Safety-Performance Evaluation of Roadside Features.” The resulting document was published by AASHTO as the Manual for Assessing Safety Hardware (MASH). MASH con- tains revised criteria for the safety-performance evaluation of virtually all roadside safety fea- tures (2). For example, MASH recommends testing with heavier light-truck vehicles to better represent the current fleet of vehicles in the pickup/van/sport utility vehicle class. Further, MASH increases the impact angle for most small car crash tests to the same angle as the light-truck test conditions. These changes place greater safety-performance demands on many current roadside safety features. AASHTO published the second edition of MASH (referred to as MASH-2016) in Decem- ber 2016 (3). As part of this process, the FHWA and AASHTO adopted a joint implementa- tion agreement that establishes dates for implementing MASH-compliant safety hardware for new installations and full replacements on the National Highway System (NHS). Although some barrier testing was performed during the development of the updated criteria, many barrier sys- tems and other roadside safety features have yet to be evaluated under MASH-2016. Therefore, evaluation of the remaining widely used roadside safety features using the safety-performance evaluation guidelines in MASH-2016 is needed. Many types of nonproprietary bridge rails are in use throughout the United States, and research is needed to determine which rail systems need to be retested to MASH-2016 criteria and which, if any, can be grandfathered in based on evaluation under previous criteria. In 1997, the FHWA provided a list of 74 bridge rails and their equivalent NCHRP Report 350 test levels based on testing performed under the earlier NCHRP Report 230 test levels and the performance levels in the AASHTO guide specification for bridge rails (4). In 2000, the FHWA provided guidance that allowed for demonstrating that variations of an accepted bridge rail design did not have to be crash- tested if the basic geometry of the bridge rail had not been changed and the structural design of the rail was comparable to the rail that had been tested (5). Research Objective The approach for this project was to perform nonlinear FE simulations and crash testing to gen- erate/update the graphs in Figures A13.1.1-2 and A13.1.1-3 of AASHTO LRFD (6) to account for the MASH-2016 increased impact severity. The post setback distance, vertical clear opening, and C H A P T E R 1 Background and Objective

4 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance ratio of contact width to rail height were all evaluated according to these figures. In addition, the loading and height information as shown in AASHTO LRFD Table A13.2-1 was updated for the current MASH-2016 specifications. The bridge rail systems that were considered “marginal” and “not satisfactory” for the geo- metrics evaluation criteria in Silvestri-Dobrovolny et al. (7) were reevaluated based on the new geometric criteria and by conducting full-scale impact simulations on these systems. Also, one bridge rail system considered not satisfactory for the strength evaluation criteria in Silvestri- Dobrovolny et al. was reevaluated using full-scale impact simulations on the system. These bridge rail systems represent the majority of rails currently used in the United States. Imple- menting these items will provide state department of transportation (DOT) engineers, designers, and others current information for designing bridge rail systems according to MASH-2016 specifications. General Discussions MASH Implementation Plan MASH is the latest in a series of documents that provide guidance on testing and evaluating roadside safety features. First published in 2009 (2), it represents a comprehensive update to crash-test and evaluation procedures to reflect changes in the vehicle fleet, operating conditions, and roadside safety knowledge and technology. MASH supersedes NCHRP Report 350: Recom- mended Procedures for the Safety Performance Evaluation of Highway Features (1). AASHTO and the FHWA adopted a MASH implementation plan with compliance dates for installing MASH hardware that differ by hardware category. Figure 1.1 shows the different dates and associated roadside safety hardware categories. According to the plan, all new installations of roadside safety devices on the NHS on projects let after December 31, 2019, must be MASH- compliant. These were the original proposed dates and have been subject to changes over the past months. The FHWA no longer issues eligibility letters for highway safety hardware under previous performance criteria. The FHWA released an open letter dated May 26, 2017, saying it is implementing immediate process changes on how requests for federal-aid eligibility letters for roadside safety hardware systems are accepted. The full letter is in Appendix A; the following is excerpted: 1. Moving forward, in order for manufacturers and States to qualify for a[n] FHWA Federal-aid eligibility letter, all roadside hardware devices must complete the full suite of recommended tests as described in AASHTO MASH. This applies to: a. all devices currently in the FHWA queue that have not received an eligibility letter by the effective date of this letter and, b. retroactively to requests received after January 1, 2016. Manufacturers and States that received an eligibility letter under AASHTO’s MASH stan- dards and did not run the full suite of tests will be required to run the remaining tests in order to retain the Federal-aid eligibility letter. . . . 2. FHWA will no longer provide Federal-aid eligibility letters for modifications made to an AASHTO MASH-crash tested device. The FHWA will no longer accept and review any eligibility requests based solely or in part on engineering analysis. However, the eligibility justification can still be reviewed and considered by individual state DOTs. As of the submission of this report, the FHWA eligibility process for crash-tested systems is undergoing further discussion.

Background and Objective 5   MASH Major Changes and Implications MASH was developed to incorporate significant changes and additions to the procedures for assessing the performance of roadside safety hardware, including new design vehicles that better reflect the changing character of the vehicles using the highway network. For example, MASH increased the weight of the pickup truck design test vehicle from 4,409 to 5,000 lb., changed the body style from a ¾-ton standard cab to a ½-ton four-door cab, and imposed a minimum height for the vertical center of gravity of 28 in. The increase in vehicle mass represents an increase in impact severity of approximately 13% from the impact conditions of NCHRP Report 350. The increased impact severity may, therefore, result in increased impact forces and larger lateral barrier deflections compared to NCHRP Report 350 impact conditions. The impact conditions for the small-car test have also changed. The weight of the small passenger design test vehicle increased from 1,800 to 2,420 lb., and the impact angle increased from 20 to 25 degrees. These changes represent an increase in impact severity of 206% for Test 3-10 with the small-car design test vehicle from the impact conditions of NCHRP Report 350. This increase in impact severity might result in increased vehicle snagging and occupant compartment defor- mation and could aggravate vehicle stability during impacts with certain types of barriers. Similar to NCHRP Report 350, MASH defines six test levels for longitudinal barriers. Each test level places an increasing standard of demand on the structural capacity of a barrier system. At a minimum, all barriers on high-speed roadways on the NHS are required to meet Test Level 3 (TL-3). The structural adequacy test for this level consists of a 5,000-lb pickup truck (denoted 2270P) impacting the barrier at 62 mph at an angle of 25 degrees. The severity test consists of a 2,420-lb. passenger car (denoted 1100C) impacting the barrier at the same speed and angle. Most state DOTs require their bridge railings and median barriers to meet Test Level 4 (TL-4), which includes a test with a 24,240-lb. single-unit truck (denoted 10000S) impacting the barrier at 56 mph at an angle of 15 degrees. Higher containment barriers are sometimes used when conditions—such as a high percentage of truck traffic or the nature of a hazard underlying a bridge—warrant it. Higher test levels (e.g., TL-5 and TL-6) include evaluation with 36,000-lb. tractor-van trailers and tractor-tank trailers. Such barriers are necessarily taller, stronger, and more expensive to construct. Under Texas Department of Transportation (TxDOT) Research Project 9-1002, Sheikh et al. investigated the minimum height and lateral design load for MASH TL-4 bridge rails (8). Under MASH, the severity of TL-4 impacts increased 56% compared to NCHRP Report 350. Conse- quently, 32-in.-tall barriers that met TL-4 requirements under NCHRP Report 350 do not satisfy Figure 1.1. MASH implementation deadlines for roadside safety devices.

6 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance MASH. The minimum rail height for MASH TL-4 barriers was determined to be 36 in. The lat- eral design impact load was found to vary with rail height. For a 36-in.-tall barrier (the minimum height required to meet stability requirements for the single-unit truck), the design impact load is 68 kip. As the height of the barrier increases, more of the cargo box of the single-unit truck is engaged and the lateral load on the barrier increases. For a barrier height of 42 in., the lateral design impact load is 80 kip. NCHRP Project 20-07/Task 395 Introduction The research team conducted a thorough review of all the information and data generated under NCHRP Project 20-07/Task 395 by Silvestri-Dobrovolny et al. (7). All the information that relates to stability, strength, and geometric characteristics for TL-2 through TL-5 bridge rail systems was reviewed and incorporated as necessary for this project. All available crash-testing information is also included in this report. Identification and Prioritization of Bridge Rail Systems Silvestri-Dobrovolny et al. prepared and distributed an electronic survey seeking input from state DOTs, the AASHTO Technical Committee for Roadside Safety, the AASHTO Subcommittee on Bridges and Structures, and Technical Committee T-7 “Guardrail and Bridge Rail.” The survey requested information regarding the type and frequency of use of nonproprietary domestic bridge rails in each state. Additionally, for each of their bridge rail systems, the DOTs were asked whether they intended to discontinue its use or pursue MASH eligibility. The information was collected through a web-based survey instrument. Follow-up telephone and email communica- tions were made to resolve questions, clarify information, or request additional input. The web- based survey was emailed to appropriate contact persons in each state. AASHTO helped the research team identify appropriate contact persons and information. In addition to verifying the types of bridge rails currently in use, the survey requested rela- tive frequency of use for each rail type and whether the state planned to discontinue use of the bridge rail system or pursue MASH eligibility to permit its continued use on the NHS beyond the implementation date. Silvestri-Dobrovolny et al. analyzed the information and determined what bridge rails were most frequently used and would therefore be high-priority for evaluation to MASH criteria. A total of 34 survey responses were collected from 33 DOT agencies and FHWA federal lands. Silvestri-Dobrovolny et al. reviewed and organized the survey responses based on the following bridge rail categories and subcategories: • Concrete only – Vertical profile – Vertical profile, post and beams – New Jersey profile – Single slope profile – F-shape profile • Metal only – Deck-mounted – Side-mounted

Background and Objective 7   • Concrete metal combined (traffic only) – With curb ◾ Three metal members ◾ Two metal members ◾ One metal member – With parapet ◾ Three metal members ◾ Two metal members ◾ One metal member • Combination traffic-pedestrian – With sidewalk – Without sidewalk • Wood only • Noise wall only • Retrofit only The bridge rails in each category were ranked in order of weighted frequency of use (WFofU). Each rail system was assigned a weighted value based on the reported frequency of use from a DOT. The number represented the WFofU of a DOT for that specific bridge rail system at the considered test level. The WFofU for a given bridge rail system for a specific test level was defined as the sum of all contributing WFofU values reported by the DOTs for that specific bridge rail system at that specific test level. Table 1.1 summarizes the rankings based on WFofU for each proposed barrier category. These prioritized railing types were considered for further investigation and evaluation for MASH equivalency. Method for Evaluating Test Level Equivalency As part of the effort to evaluate equivalency between NCHRP Report 350 and MASH test levels, three key criteria were explored in Silvestri-Dobrovolny et al. (7): stability, strength, and geo- metrics. Stability relates to all the characteristics of the barrier that affect vehicle stability, such as barrier height, barrier shape, and barrier stiffness. Strength consists of all the features of the barrier that affect the ability of the barrier to effectively contain and redirect the vehicle into the travel lane shoulder and all factors of the barrier that prevent the vehicle from penetrating the barrier. The geometrics category is all geometric features of the bridge rail that affect occupant risk criteria in MASH. These include post setback, clear opening between longitudinal rail elements, and avail- able vertical contact surface area. These factors can influence key performance metrics such as vehicle snagging, occupant compartment deformation, and acceleration-based occupant risk indices. Descriptions of these three criteria and the relevance of the results to assessing test level equivalencies are discussed below. TL-2 and TL-3 Bridge Rail Systems Stability Requirements. The static stability of the MASH 2270P pickup truck is similar or slightly improved compared to the NCHRP Report 350 2000P pickup truck. Anecdotal crash test experience supports improved stability of the MASH 2270P pickup truck. Crash test compari- sons of two similar rails were inconclusive regarding relative stability of the two vehicles. To help evaluate vehicle stability, Silvestri-Dobrovolny et al. conducted FE simulations with the MASH pickup truck vehicle impacting a rigid wall at varying barrier heights of 27, 28, and 29 in. The simulation with a 27-in. barrier resulted in rollover of the truck. The simulation with a 28-in. barrier did not roll over but was on the edge of instability. The simulation with a 29-in.

8 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance Table 1.1. Ranking based on WFofU per category—survey results.

Background and Objective 9   barrier did roll after impact with the vertical wall but was fairly stable throughout the impact event. Based on the results from the simulations, the minimum recommended rail height for MASH TL-3 bridge rails is 29 in. This is higher than NCHRP Report 350’s minimum of 27 in. for bridge rails. Bridge rail systems successfully tested under NCHRP Report 350 TL-3 impact conditions should generally be adequate for the equivalent TL-3 under MASH. Strength Requirements. MASH Test 11 with the 2270P pickup truck has a higher impact severity and greater impact load compared to NCHRP Report 350 Test 11 with the 2000P truck for both TL-2 and TL-3. Consequently, TL-2 and TL-3 bridge rail systems will require addi- tional capacity. However, current estimates of impact load and resultant height indicate NCHRP Report 350 TL-3 bridge rails may have significant reserve capacity. This reserve capacity appears to be sufficient to accommodate the increased capacity demand associated with MASH impact conditions. Geometric Requirements. Silvestri-Dobrovolny et al.’s initial assessment of the impact performance of post-and-beam bridge rail systems under MASH guidelines indicated that the current geometric relationships for bridge rail design in Section 13 of AASHTO LRFD (6) still have some validity for both the small passenger car and the pickup truck, and that bridge rail systems designed to meet these geometric relationships under NCHRP Report 350 may satisfy MASH. Given the significant increase in impact severity of MASH Test 10 with the 1100C small passenger car design test vehicle due to increases in both vehicle weight and impact angle, this finding may be important to establishing test level equivalencies. This conclusion is based on a limited amount of data and tests conducted according to MASH, and as more data become avail- able, the geometric data should continue to be updated and analyzed. Geometric Requirements for Specific Bridge Rail Categories. Silvestri-Dobrovolny et al. concluded that a global equivalency can be confidently established for parapet-mounted metal post-and-beam systems that have a concrete parapet height greater than or equal to 24 in. The parapet height requirement was selected by the researchers to mitigate potential wheel and bumper snagging with MASH small car and pickup truck vehicles. TL-4 Bridge Rail Systems Stability Requirements. Sheikh et al. investigated the minimum rail height requirement and lateral design load for MASH TL-4 bridge rails (8). The researchers employed FE analysis and crash testing to determine the minimum rail height for MASH TL-4 impact conditions, which was determined to be 36 in. This was verified with a MASH TL-4 test of a 36-in.-tall single- slope barrier. Therefore, Sheikh et al. recommend a 36-in. minimum rail height for MASH TL-4 bridge rail systems. Strength Requirements. MASH Test 4-12 with the single-unit truck has a higher impact severity and greater impact load compared to NCHRP Report 350 Test 4-12. Consequently, MASH TL-4 bridge rail systems will require additional capacity. However, current estimates of impact load and resultant height indicate NCHRP Report 350 TL-4 may have substantial reserve capacity. This reserve capacity appears to be sufficient to accommodate the increased capacity demand associated with MASH TL-4 impact conditions. This is primarily due to having improved estimates of load application heights using advanced FE impact simulations. Geometric Requirements. Geometric requirements for MASH TL-4 bridge rails are the same as for MASH TL-3 bridge rails with the exception of rail height, which will be a minimum of 36 in. It is likely that some TL-4 bridge rails will be designed with a height greater than 36 in.

10 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance to provide improved stability for heavy-truck impacts and to accommodate future pavement overlays. Although not a specific MASH evaluation criterion, consideration should be given to the potential for occupant head excursion and contact with components of the bridge rail system for these taller barriers—testing to date has not found this to be a problem with existing rails. TL-5 Bridge Rail Systems The impact conditions associated with MASH Test 5-12 with the 36000V tractor-van trailer have not changed from NCHRP Report 350 to MASH. Therefore, Silvestri-Dobrovolny et al. concluded that an extensive evaluation of NCHRP Report 350 TL-5 bridge rails was not required. Stability Requirements. The vehicle mass, impact speed, and impact angle have not changed from NCHRP Report 350 TL-5 to MASH TL-5. The impact severity has therefore not changed for MASH TL-5. The minimum rail height for MASH TL-5 impacts remains 42 in. There are several 42-in. barriers that have met NCHRP Report 350 and MASH TL-5 requirements. Recently, Williams et al. designed and successfully tested a new MASH TL-5 bridge rail for TxDOT (9). This new barrier, known as the T224, was designed with openings to provide some aesthetic characteristics. It is believed to be the first TL-5 bridge rail to incorporate openings into the rail design. The system was tested on an 8½-in.-thick concrete deck cantilever, which is thinner than decks previously designed for TL-5 rails. The TxDOT T224 met all the strength and performance requirements of MASH TL-5 when tested with a 36000V tractor-van trailer with the new 53-ft. trailer now permitted under MASH 2016. Strength Requirements. As part of NCHRP Project 22-20(02), Bligh et al. conducted FE analyses to determine impact loads associated with the MASH 80,000-lb. tractor-van trailer vehicle for different barrier heights under TL-5 impact conditions (10). The barrier heights analyzed were selected to cover the range of heights of previously crash-tested TL-5 barriers. A tall, rigid wall provided information on the maximum impact load associated with a TL-5 impact. The simulation data were used to determine the dynamic load in the lateral, longitu- dinal, and vertical directions. The distribution of the lateral impact load in the longitudinal and vertical directions of the barrier was also investigated. Barrier height was found to have a dra- matic effect on the peak lateral load: above 42 in., the trailer floor engaged the barrier, resulting in a significant increase in force applied to the barrier. The peak lateral loads associated with the taller barriers were greater than the load measured in the instrumented wall tests conducted in the 1980s. The primary reason for this is the differ- ence in ballast. Many of the early tests conducted with tractor-van trailers used sandbags and hay bales for ballast. Because the ballast was not rigidly secured to the floor of the trailer, it could shift during impact, resulting in lower forces on the barrier. While these are still considered an acceptable type of ballast, MASH states “ballast should be firmly secured to prevent movement during and after the test.” This results in higher impact loads transmitted to the barrier. Although the results of this project indicate a potential need to update the TL-5 design impact loads in Section 13 of AASHTO LRFD (6), that need is not necessarily material to the evalua- tion of TL-5 bridge rails under this project. As discussed, the impact conditions—and thus the impact severity—have not changed for MASH TL-5. Therefore, if a TL-5 bridge rail were success- fully crash-tested in accordance with NCHRP Report 350 and the ballast inside the trailer were properly restrained, the barrier should have sufficient capacity for MASH TL-5 and no further strength analyses would be needed. Geometric Requirements. Geometric requirements for MASH TL-5 bridge rails are the same as for MASH TL-3 bridge rails. Consideration should be given to the potential for occupant head excursion and contact with components of the bridge rail system for taller TL-5 barriers

Background and Objective 11   when tested with smaller vehicles. Testing of 42-in. TL-5 barriers to date has not indicated a problem in this regard. Global Equivalency Results The resulting global equivalencies are presented in Table 1.2. All NCHRP Report 350 TL-5 bridge rail system types can be found acceptable under equivalent MASH TL-5 because the testing conditions for MASH and NCHRP Report 350 TL-5 are identical. Since the TL-3 and TL-4 test conditions and vehicle masses change between NCHRP Report 350 and MASH, NCHRP Report 350 TL-3 and TL-4 bridge rail equivalencies depend on the bridge rail type. NCHRP Report 350 TL-3 and TL-4 solid concrete parapets and metal rails on concrete parapets with a parapet height greater than 24 in. are considered acceptable under MASH TL-3. NCHRP Report 350 TL-3 and TL-4 concrete post-and-beam, metal rail deck, or curb-mounted systems can be found acceptable under MASH TL-2. Additional details can be found in Silvestri-Dobrovolny et al. (7). Rail Analysis Method Based on the global test level equivalency presented in the Method for Evaluating Test Level Equivalency section, many of the NCHRP Report 350 bridge rail systems are not eligible to be grandfathered in under MASH. These rail systems will require more detailed analyses and evalu- ation, and perhaps crash testing. This section describes the rail-specific analysis methods applied to different bridge rail categories and the results of the analyses performed on the bridge rail systems prioritized in the Identification and Prioritization of Bridge Rail Systems section of this chapter. To evaluate the prioritized bridge rail systems according to MASH, three criteria were con- sidered by Silvestri-Dobrovolny et al. (7): stability, rail geometrics, and strength. The analysis methods used to evaluate these criteria are presented here. The results of the analyses were used NCHRP Report 350 Rail System Type MASH Test Level TL-2 TL-3 TL-4 TL-5 Solid Concrete Parapet TL-2 TL-3 TL-4 TL-5 Concrete Post- and-Beam TL-2 TL-3 TL-4 TL-5 Metal Post-and- Beam Deck- Mounted TL-2 TL-3 TL-4 TL-5 Metal Post-and- Beam on Curb TL-2 TL-3 TL-4 TL-5 Metal Post-and- Beam on Concrete Parapet* TL-2 TL-3 TL-4 TL-5 * Concrete parapet height greater than or equal to 24 in. Table 1.2. Summary of global test equivalency for NCHRP Report 350 bridge rails.

12 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance to determine which rails could be considered MASH-compliant and which would require further analysis or crash testing to establish MASH compliance. Stability Requirements for MASH Bridge Rail Systems For a bridge rail system to be considered a MASH-acceptable barrier, a minimum height must be met to ensure stability of the vehicle. Table 1.3 shows the minimum height requirements for MASH TL-3, TL-4, and TL-5 bridge rail systems. As specified in Section 13 of AASHTO LRFD (6), rail height is measured to the top of the rail. If the minimum rail height was satisfied, the rail was considered to satisfactorily meet stability requirements. Geometric Requirements for MASH Bridge Rail Systems The geometric relationships for bridge railings in Section 13 of AASHTO LRFD (Figure 1.2) were applied to evaluate rail geometry. These relationships pertain to the potential for the wheel, bumper, or hood to snag on elements of the bridge rail system. Severe snagging can lead to a number of undesirable consequences including increased occupant compartment deformation, higher accelerations and occupant risk indices, and vehicle instability. For each bridge rail system analyzed, post setback distance, ratio of contact width to height, and vertical clear opening were determined or calculated from the provided bridge rail details and plotted against AASHTO LRFD Section 13 geometric criteria. Strength Requirements for MASH Bridge Rail Systems Section 13 of AASHTO LRFD contains procedures for analyzing the structural capacity of different types of bridge railings (e.g., steel, concrete). Using these procedures, Silvestri- Dobrovolny et al. performed an analysis of the strength of the rail system. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 5 10 15 R at io o f R ai l C on ta ct W id th to H ei gh t Post Setback Distance (in) Preferred Not Recommended 0 2 4 6 8 10 12 14 16 0 5 10 15 V er tic al C le ar O pe ni ng (i n) Post Setback Distance (in) High Snag Potential Low Snag Potential Figure 1.2. AASHTO LRFD Section 13 figures A13.1.1-2 and A13.1.1-3 (6). MASH Test Level Minimum Height (in.) TL-3 29 TL-4 36 TL-5 42 Table 1.3. Minimum height requirements for MASH TL-3, TL-4, and TL-5.

Background and Objective 13   For concrete parapet railings, the yield line method was applied by Silvestri-Dobrovolny et al. to determine the ultimate strength of the system. Metal rail systems were analyzed using plastic strength analysis methods. The strength of the rail members, posts, and post connections were analyzed to obtain the overall strength of the rail system. The calculated strengths of the bridge rail systems were compared to design impact loads (Table 1.4) corresponding to the relevant MASH test level. Complete structural details of the rail system were required for this task. The MASH TL-3 design impact force was determined by conducting full-scale impact simu- lations on a rigid wall. The MASH TL-4 and TL-5 design impact forces were determined by conducting full-scale impact simulations on a rigid wall and by conducting full-scale crash tests on an instrumented, mechanically stabilized earth retaining wall. Summary of Recommendations The recommendations made by Silvestri-Dobrovolny et al. are presented in Table 1.5. Rail-Specific Analysis Method Four bridge rail system analysis categories were developed for NCHRP Project 20-07/ Task 395 to encompass the various bridge rail systems that were analyzed. The four bridge rail system analysis categories were solid concrete parapet, concrete post-and-beam, steel post- and-beam, and combination steel post and concrete parapet. Silvestri-Dobrovolny et al. created analysis templates for the four different categories in Microsoft Excel to help determine the overall strength of the bridge rail systems. As previously discussed, the three criteria for analysis of a specific bridge rail system were stability, geometrics, and strength. A bridge rail system must meet all the criteria to be considered acceptable under MASH evaluation criteria for the speci- fied test level. The first section of the Silvestri-Dobrovolny et al. analysis template for each category evaluated stability. This section remained the same for each bridge rail category because the minimum rail height requirement did not change. The analyst specified the test level and height to the top of the rail as determined from the detailed drawings of the bridge rail. The stability criteria were assessed according to whether the rail height was equal to or greater than the minimum rail height. Figure 1.3 shows an example of the stability criteria portion that was used in the templates created in Silvestri-Dobrovolny et al. The second section of the template for each bridge rail category evaluated geometric criteria. For each bridge rail, post setback distance, vertical clear opening, and ratio of rail contact width to height were determined or calculated. Silvestri-Dobrovolny et al. plotted these values on AASHTO LRFD Section 13 figures A13.1.1-2 and A13.1.1-3 to assess the potential for vehicle wheel, bumper, or hood snagging. For solid concrete parapets, this section was not evaluated since there were no rail openings that provided potential for vehicle snagging. The researchers were able to make an assessment based on the location of the data points relative to the different regions of the plots. MASH Test Level Rail Height (in.) Design Impact Force (kip) Height of Design Impact Force (in.) TL-3 ≥ 29 71 (7) 19 (7) TL-4 36 68 (10) 25 (10) > 36 80 (8) 30 (10) TL-5 42 160 (10) 35 (10) > 42 262 (10) 43 (10) Table 1.4. Design impact loads.

14 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance MASH Test Level Recommendation Justification TL-3 29-in. minimum rail height Full-scale impact simulations performed under NCHRP Project 20-07 (7) Design impact force of 71 kip located at 19 in. above the roadway surface Full-scale impact simulations performed under NCHRP Project 20-07 (7) TL-4 36-in. minimum rail height Full-scale impact simulations and crash test performed under TxDOT Project 9-1002 (8) For a bridge rail system that is 36 in. tall, use a design impact force of 68 kip located at 25 in. above the roadway surface Full-scale impact simulations and crash test performed under NCHRP Project 22-20(2) (10) For a bridge rail system that is taller than 36 in., use a design impact force of 80 kip located at 30 in. above the roadway surface Full-scale impact simulations and crash test performed under NCHRP Project 22-20(2) (10) TL-5 42-in. minimum rail height Specified in NCHRP Report 350 (1) For a bridge rail system that is 42 in. tall, use a design impact force of 160 kip located at 35 in. above the roadway surface Full-scale impact simulations and crash test performed under NCHRP Project 22-20(2) (10) For a bridge rail system that is taller than 36 in., use a design impact force of 262 kip located at 43 in. above the roadway surface Full-scale impact simulations and crash test performed under NCHRP Project 22-20(2) (10) Table 1.5. NCHRP Project 20-07 recommendations. The third and final section of the template for each bridge rail category evaluated strength criteria. For each bridge rail system, Silvestri-Dobrovolny et al. conducted an AASHTO LRFD Section 13 strength analysis. Figure 1.4 shows the MASH test level design impact forces that were used in the strength analysis. Through this analysis, the total resistance of the bridge rail system was determined. This strength analysis section varied for the four bridge rail categories. The equations and analysis methods for each bridge rail category are in Silvestri-Dobrovolny et al. (7, section 4.4) and AASHTO LRFD (6, Section 13). Rail-Specific Evaluation Assessment Designations For each bridge rail system analyzed in Silvestri-Dobrovolny et al., an assessment was made for the three evaluation criteria (stability, geometrics, and strength). In addition, an overall rail assessment was made. For each assessment, a designation of not satisfactory, satisfactory, or marginal was assigned. Figure 1.3. Stability criteria evaluation.

Background and Objective 15   Not Satisfactory. The not satisfactory (NS) designation was considered by Silvestri- Dobrovolny et al. for stability, geometrics, and strength criteria, as well as for the overall assess- ment of the bridge rail system. An NS designation was given for stability when the bridge rail system’s height did not meet the minimum MASH height requirements. An NS designation was given for geometrics when the bridge rail system’s geometrics plotted in the unacceptable or not recommended region. The researchers found that some systems in this region passed MASH testing criteria; therefore, further testing and evaluation could prove that systems with an NS designation for the geometrics criteria are indeed MASH-compliant. An NS designation was given for strength when the bridge rail system’s capacity did not meet the minimum MASH strength requirements. The strength analysis procedure used to evaluate the bridge rail systems in Silvestri-Dobrovolny et al. was conservative; therefore, further testing and evaluation could prove that systems with an NS designation for strength criteria are MASH-compliant. Satisfactory. The satisfactory (S) designation was considered by Silvestri-Dobrovolny et al. for stability, geometrics, and strength criteria, as well as for the overall assessment of the bridge rail system. An S designation was given for stability when the bridge rail system’s height met the minimum MASH height requirements. An S designation was given for geometrics when the bridge rail system’s geometric data points plotted in the acceptable or preferred region. An S designation was given for strength when the bridge rail system’s capacity exceeded the MASH design impact load. Marginal. The marginal (M) designation was considered by Silvestri-Dobrovolny et al. only for the geometrics criterion. An M designation was specified when the rail geometrics plotted between the not recommended and preferred lines or low snag potential and high snag potential lines of AASHTO LRFD Section 13 Figures A13.1.1-2 and A13.1.1-3, respectively. Figure 1.5 gives an example of a data point plotting between the two regions. An M designation was given for this range because limited MASH crash tests have been performed, and some tests that plotted in this region were failures according to MASH. For this reason, Silvestri-Dobrovolny et al. could not confidently assess the geometrics of bridge rails whose characteristics plotted between the preferred and not recommended regions of the relationships. This does not mean the bridge rail system would not pass MASH crash testing. In fact, some systems that plotted in this region did pass MASH testing criteria. Thus, an M designation was assigned to those bridge rail systems that plotted in this region. Additional crash testing and evaluation is recommended to assess these bridge rails according to MASH. Figure 1.4. Design forces for bridge railings.

16 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance A flow diagram of the rail-specific evaluation assessment designation process for the three evaluation criteria is presented in Figure 1.6. Overall Assessment. Silvestri-Dobrovolny et al. determined that an overall assessment of satisfactory can only be assigned to a bridge rail system that has been given a designation of S for all three evaluation criteria (stability, geometrics, and strength). With an S overall assessment, the researchers concluded the investigated bridge rail system was MASH-compliant and no further 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 2 4 6 8 10 12 R at io o f R ai l C on ta ct W id th to H ei gh t Post Setback Distance (in.) Preferred Not Recommended Figure 1.5. Example of data point resulting in marginal designation. Figure 1.6. Rail-specific evaluation assessment designation process.

Background and Objective 17   testing was needed. If any of the three evaluation criteria was given an M or NS designation, an NS overall designation was assigned to that bridge rail system. An NS overall assessment did not mean the investigated bridge rail system would not meet MASH criteria; it merely indicated that a determination regarding MASH compliance could not be made without further testing. Rail-Specific Analyses Silvestri-Dobrovolny et al. evaluated the prioritized bridge rail systems identified in the Identi- fication and Prioritization of Bridge Rail Systems section using the analysis procedures described in the Rail-Specific Analysis Method section. The resulting assessment for each analyzed bridge rail system is summarized in Table 1.6. Table 1.6. Rail-specific evaluation results. NCHRP Report 350 Test Level Category Subcategory System Name Evaluated MASH Test Level Stability Geometrics Strength Overall Assessment TL-4 Concrete Only F-Shape 32-in. F-Shape (WV, PA, VA, LA, OR, MA, ME, FL, WS, TX) TL-4 NS — — NS TL-3 S S S S 42-in. F-Shape ( ME, FL, WS) TL-4 S S S S TL-4 Concrete Only Single Slope 42-in. Single Slope (WV, PA, VA, LA, OK, MD, MA) TL-4 S S S S 36-in. Single Slope (TX, TN) TL-4 S S S S TL-4 Combined (Traffic) Curb, 2 Metal Members Alaska Multistate Bridge Rail— 32.5 in. (AK) TL-4 NS — — NS TL-3 S S S S Two-Tube Railing 36d (WY) TL-4 NS — — NS TL-3 S M S NS TL-4 Combination Traf/Ped Traf/Ped, w/Sidewalk T4 Steel Bridge Rail (NH) TL-4 S M NS NS S-352 Series, Bridge Railing, Galvanized Steel Tubing/Concrete Combination (VT) TL-4 S S S S TL-5 Concrete Only F-Shape 42-in. F-Shape (WV, PA, VA, OK, MD, MA) TL-5 S S S S 45-in. F-Shape (IN) TL-5 S S S S TL-4 Concrete Only Post-and- Beam Kansas Corral 32 in. without Curb (VA) TL-4 S M NS NS Open Concrete Rail, 2 ft. 10 in. height (NE) TL-4 NS — — NS TL-3 S M S NS (continued on next page)

18 Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance NCHRP Report 350 Test Level Category Subcategory System Name Evaluated MASH Test Level Stability Geometrics Strength Overall Assessment TL-4 Metal Only Deck Mounted Type A42 Metal Bridge Railing (NM) TL-4 S S S S TL-4 Combined (Traffic) Parapet, 2 Metal Members Bridge Railing, Aesthetic Parapet Tube (B- 25-J) (MI) TL-4 S S S S TL-3 Combination Traf/Ped Traf/Ped, w/Sidewalk Concrete Parapet with Structural Tubing STD-11- 1 (TN) TL-3 S S S S TL-4 Retrofit Retrofit Concrete Baluster Thrie Beam Retrofit (WA) TL-4 S S NS NS Note: — indicates criterion was not evaluated. TL-4 Combination Traf/Ped Traf/Ped, w/out Sidewalk S3-TL4 (MA) TL-4 S M S NS 4-Bar Steel Traffic/Bicycle Railing (on curb) (ME) TL-4 S M S NS TL-3 Combination Traf/Ped Traf/Ped, w/out Sidewalk George Washington Memorial Parkway (Federal Lands) TL-3 S M S NS C221 (TX) TL-3 S M S NS TL-3 Combined (Traffic) Curb, 2 Metal Members WY Two Tube (TL-3) SBB36c (WY) TL-3 S NS S NS TL-4 Metal Only Side Mounted Side-Mounted Metal Bridge Railing (NM) TL-4 NS — — NS TL-3 S M S NS Table 1.6. (Continued).