Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments (2022)

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35   C H A P T E R 3 The objective of rigid barrier crash data analysis was to use full-scale crash testing and simula- tion to investigate the maximum vehicle extension over rigid barriers, additional vehicle-barrier interactions, and possible relationships between maximum extension into the ZOI and barrier height. These relationships were used to validate simulation models to more accurately predict ZOI as a function of barrier height and generate recommended ZOI envelopes. Maximum vehicle extent was primarily evaluated through past full-scale crash testing; prior simulation was used for supplementary evaluation if necessary. Similar to the previous ZOI study (Keller et al. 2003), only critical vehicle components were included when determining ZOI envelopes. Critical vehicle components may pose a risk to vehicle occupants or impart a significant load to fixed objects within the ZOI. These components included the engine hood, fender, door, roof, and cargo box but did not include non-structural components such as plastic bumpers and side mirrors. 3.1 Rigid Barrier Crash Test Database Reports from rigid barrier crash tests conducted under MASH criteria were collected; some NCHRP Report 350 TL-5 crash tests (Ross et al. 1993) were included as TL-5 was very similar under NCHRP Report 350 and MASH. The complete crash database is shown in Appendix A. Failed crash tests were excluded from analysis, as were crashes with unavailable or restricted data. Thus, ZOI was measured using video from 47 full-scale crash tests. As shown in Table 7, two tests were conducted under MASH TL-2 criteria, 31 under MASH TL-3, eight under MASH TL-4, and six under MASH TL-5. Although MASH TL-4 and TL-5 included passenger vehicle tests, tests associated with MASH test designation nos. 4-11 and 5-11 were included with the MASH TL-3 measurements based on similarities of the vehicles. Thus, MASH TL-4 and TL-5 conditions only included results of test designations nos. 4-12 and 5-12, which utilized SUTs and tractor-trailers, respectively. 3.2 ZOI Measurement from Video ZOI measurements were taken from full-scale crash tests to evaluate the range of lateral and vertical extensions of vehicle components at different MASH test levels. Downstream, upstream, and overhead high-speed videos were used to isolate the maximum extent of critical components when available. Oblique or obscured views were not used to estimate ZOIs. For all measurements, the reference point (i.e., measurement origin) was the top-front corner of the traffic side of the barrier. Virtual intersections of the top and traffic-side faces were used for barriers with chamfered or rounded edges on the top edge of the traffic-side face. In Rigid Barrier Crash Data Analysis

36 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments each camera view, a reference object with a known length, such as the barrier-top width or a measured vehicle component, was necessary to establish a reference plane to calibrate measure- ments. It was important to establish the reference distance near where maximum vehicle intru- sion occurred to record accurate measurements. At least three measurements were recorded for each test: • Maximum lateral extent behind the front barrier face. • Height corresponding to the point of maximum lateral extent. • Maximum height of intrusion over front barrier face along the vertical plane of the traffic- side face. For many tests, additional measurements were taken to better define the space occupied by criti- cal vehicle components behind the leading barrier-top edge. These measurements included SUT box extension below and behind a barrier when it protruded over the top of a rail and lateral and vertical extents of several stiff vehicle components that protruded behind the barriers at different times in the impact sequence. Examples of ZOI measurements are shown in Figures 32 through 34. ZOI measurements and corresponding times for each component’s maximum extension were recorded for each test. Vehicle intrusion zones were created by connecting all measured points of maximum lateral and vertical extents at any time throughout impact with straight lines and were differentiated by barrier shape, height, test vehicle, and impact conditions. The risk of occupant injury associated with an SUT or tractor-truck cab snagging on a traffic barrier attachment was significantly greater than associated cargo box snagging. Thus, for MASH Barrier No. Crash Tests TotalTL-2 TL-3 TL-4 TL-5 Jersey 0 7 0 2 9 F-shape 0 0 0 0 0 Single slope 0 5 5 2 11a Vertical 0 6 1 2 9 Steel combination 2 9 2 0 13 Low profile 0 0 0 0 0 Other 0 4 0 0 5a Total 2 31 8 6 47 a Totals reflect one shape was retroactively reclassified. Table 7. Barrier types by test level with available ZOI data. Figure 32. MASH TL-3 ZOI measurement example (Bielenberg 2019).

Rigid Barrier Crash Data Analysis 37   Figure 33. MASH TL-4 ZOI measurement example (Rosenbaugh et al. 2021). Figure 34. MASH TL-5 ZOI measurement example (Rosenbaugh, Sicking, and Faller 2007). test designation nos. 4-12 and 5-12, ZOI envelopes were determined for both the cab and cargo box zone. Although the cab zones were smaller than the box or trailer zones, the reason for separating cab zones was because occupants are located in the cab zones, and safety is an important consideration, but impact between the box or trailer with a shielded object could be acceptable in some circumstances. While the measurement procedure was as comprehensive as possible, some limitations likely affected accuracy: • Camera lenses skew or fish-eye near the extremities of the frame. When film analysis is con- ducted for a full-scale crash test, lens corrections are usually applied to account for skew. However, lens corrections were not available nor applied to these videos.

38 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments • Some camera views in large-truck tests did not capture the full height and width of the box extension. In some cases, the height of extension was estimated. • Precise measurements were more difficult in views with a large field of view. Debris such as dust or disengaged vehicle components may also obstruct a view. • To capture the vertical extent of the ZOI, an upstream or downstream camera view is required. Due to camera perspective, the length of the reference object needs to occur at approximately the location where maximum intrusion over the barrier occurs; this can be difficult to deter- mine precisely. The magnitude of measurement errors was unknown. However, researchers believed there was no propensity for errors to underestimate or overestimate ZOI measurements, and thus overall ZOIs would be sufficient. These limitations are discussed further in Section 8.1. Researchers compared working widths denoted in test reports—that is, the distance between the front-most section of the barrier before impact to the rearmost extension of stiff barrier or vehicle components dynamically during a test—to the researcher-measured maximum ZOI values to confirm that ZOI measurements were reasonable. The maximum horizontal extent of the ZOI was similar to reported working widths, which must be documented per MASH requirements (AASHTO 2016); however, they were not the same measurement. Working width was measured from the farthest forward point on the barrier to the maximum system or vehicle extent beyond this point. Thus, when the vehicle did not extend beyond the back barrier face, the working width was equal to barrier width. When the vehicle extended beyond the back barrier face, working width was the distance from the farthest forward point to the vehicle extent or maximum lateral deformation of a barrier component. ZOI was measured from the top-front barrier corner to the maximum vehicle extent. When barriers were vertical, the top-front barrier corner was often equal to the farthest forward point on the barrier, but this was not true for other barrier shapes such as single slope, F-shape, New Jersey, or combination rails. Addition- ally, working width was measured as the maximum extent of any attached vehicle component, including both structural and non-structural components; ZOI only included critical vehicle components. Each testing agency may have different procedures for measuring working width. Therefore, while similar, ZOI and working width were usually not the same value, and compari- sons served only as an approximate accuracy check. 3.3 Preliminary ZOI Envelopes A series of preliminary ZOI envelopes were developed that encompassed the test data mea- sured from high-speed video analysis and sequential images photogrammetric reconstruction. The preliminary ZOI envelopes were drawn conservatively using rectangular extents corresponding to maximum and minimum vertical extents and maximum lateral extents. The preliminary ZOI envelopes are shown in Appendix C. These envelopes were further refined using simulation data comparisons as shown in Chapter 5. Initial observations of the results of the literature review indicated that while MASH testing has been performed at increased IS values and kinetic energies, a combination of vehicle design, stiffness properties, and revised barrier configurations resulted in the reduction of some ZOI envelopes. For example, for MASH TL-3 impact conditions, the ZOIs observed for all MASH TL-3 tests were less than the ZOI recorded for several tests performed according to the TL-3 impact conditions described in NCHRP Report 350 (Ross et al. 1993) and as shown in Figure C-15 in Appendix C. It is believed that the combination of (1) modified vehicle geometries and the evolution of vehicle frame designs (see Section 8.8.1), (2) differences in component geom- etries, and (3) proximities of the frame and chassis components to the external vehicle compo- nents is different when comparing two test vehicles: the ¾-ton pickup truck used for full-scale

Rigid Barrier Crash Data Analysis 39   testing conditions as per TL-2 and TL-3 impact conditions described in NCHRP Report 350 (Ross et al. 1993) compared to the ½-ton, full-size quad cab pickup truck used for TL-2 and TL-3 impact conditions described in MASH (AASHTO 2016). Furthermore, during the evaluation of roadside barriers according to MASH TL-2 and TL-3 impact conditions, pickup trucks com- monly used in crash testing underwent multiple revisions to chassis design, which may affect subsequent ZOI evaluation. It is not the intent of MASH, the RDG, nor this document to iden- tify a specific vehicle with the greatest propensity for intruding into the ZOI, but rather a general observation of the potential for a bad outcome to occur in the event of a collision adjacent to a fixed object located close to a rigid barrier. For this reason, conservative estimates of ZOIs were considered based on test and simulation data for all MASH test levels. The conservative estimates should be interpreted as reasonable upper bounds of the lateral and vertical extents of vehicle intrusion behind the barrier but may not indicate if occupant-risk criteria would be violated in the event of stiff vehicle component impact with a shielded feature. 3.4 Investigation of Vehicle and Rigid Barrier Interaction Rigid barrier crash tests were reviewed to determine factors affecting ZOI, including vehicle- barrier friction, vehicle suspension failure, and tire deflation. While no common parameters were found across the tests, the interaction between test vehicles and rigid barriers was used to develop more accurate simulation models in Phase II. In general, test vehicles and rigid barriers interacted similarly between tests involving compa- rable barrier types. During vehicle-to-barrier crashes, the impact-side front corner of passenger vehicles usually experienced significant damage, including wheel and suspension failure. Test vehicles and impact conditions in each class were similar, so vehicle body stiffness and suspen- sion part failure levels were believed to be consistent. Loading to the impact-side bumper, hood, and fender was also believed to be consistent based on similarities in vehicle damage, accelera- tions, and post-impact trajectories. However, wheel and suspension failures were less consistent and predictable than body dam- age. Typically, full-scale test vehicles experienced either (1) the wheel and tire remained attached and the vehicle crushed laterally and longitudinally backward toward the toe pan and/or firewall or (2) suspension connections fractured or released, and the wheel disengaged from the vehicle. Wheel disengagement and suspension failure may vary based on barrier height and geometry (e.g., cutouts, rubrails, post-and-rail configurations) or vehicle make, model, and age. Researchers have been unable to accurately predict wheel and suspension failure. It was believed loading of parts varied significantly as suspension components did not fail consistently across comparable tests. Based on the variability of suspension failures, researchers investigated several parameters affecting test vehicle behavior during impacts, which were considered during Phase II. 3.4.1 Vehicle-Barrier Friction Vehicle-barrier friction can be subdivided into tire- and sheet-metal-barrier friction, which varies based on barrier material (e.g., steel, concrete) and surface (e.g., smooth galvanized finish, aesthetic features). Rubber-concrete typically has a coefficient of friction between 0.6 and 0.85 (Engineering Toolbox 2004). Coefficients of friction for steel-on-steel range from 0.5 to 0.8 (Engineering Toolbox 2004), but galvanizing, painting, and other surface treatments can dramati- cally reduce this. Steel-concrete and rubber-steel coefficients of friction were not readily available and thus unknown without further testing. MwRSF developed a procedure to estimate lateral and longitudinal barrier loading as well as barrier friction (Eller 2007). Longitudinal and lateral vehicle accelerations from each test,

40 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments as measured at the vehicle’s center of gravity (c.g.), were processed using a CFC60 filter and a 50-millisecond (msec) moving average. The 50-msec moving average vehicle accelerations were combined with the uncoupled yaw angle versus time data to convert the accelerations to a global longitudinal and lateral coordinate system parallel and perpendicular to the barrier. The vehicle mass was multiplied by global accelerations to estimate vehicular loading applied laterally and longitudinally to the barrier. The dynamic coefficient of friction was estimated at each time step by dividing longitudinal barrier force by lateral barrier force. The dynamic coefficient of friction was averaged to deter- mine an effective, average coefficient that included both tire- and sheet metal-barrier interaction. Using this procedure, the vehicle-barrier coefficient of friction was estimated during several MASH rigid barrier tests, as summarized in Table 8; in some tests, a coefficient range was estimated. The coefficient of friction varied depending on the time range over which it was averaged, as some large instantaneous frictions occurred, especially near the beginning of the event. The friction was only calculated during the initial impact, before major suspension failure or tire deflation occurred. In some tests, especially test nos. 4CBR-1 (Rosenbaugh et al. 2021), H34BR-1 (Bielenberg 2019), and STBR-3 (Pena et al. 2020), the estimated coefficient of friction range varied signifi- cantly. However, in other tests, the average coefficient was relatively constant even when varying the time range; thus, a single coefficient of friction was estimated. While there was a small sampling of tests, the vehicle-barrier coefficient of friction was typically around 0.28 to 0.29 for concrete barriers and 0.11 to 0.13 for steel barriers. After tire deflation, loading between the barrier and wheel changes, including variation in the center of load on the wheel hub, tire-barrier friction, and suspension orientation. These varia- tions can affect vehicle behavior as it rides up the barrier. Large trucks may have solid-axle front suspensions and likely have a ZOI extension more dependent on front axle engagement than passenger vehicles. Accelerometer data used to calculate the friction loads varied too much to quantify changes directly linked to suspension failure or tire deflation. Simulations often use an averaged, overall friction coefficient. From Section 2.4, typical fric- tion coefficients ranged from 0.05 to 0.4 for effective vehicle-barrier friction and 0.1 to 0.45 for tire-barrier friction. The estimates from MASH crash tests fell within these ranges. 3.4.2 Quarter Panel Crush Stiffness The stiffness of the impacting vehicle’s front quarter panel (“fender”) has a significant effect on the potential for snag and engagement with features in a barrier’s ZOI. Structurally stiff, well- connected quarter panel components could contribute to vehicle snag and increased occupant risk if the protruding quarter panel engages a stiff, fixed object on the back side of the barrier. Test Designation No. Test No. Barrier Type Peak Load (kips) Estimated Friction CoefficientLateral Longitudinal 3-10 H34BR-1 Concrete 58.7 16.0 0.29–0.68 3-11 H34BR-2 Concrete 88.6 21.6 0.29 KSFRP-1 Concrete 76.2 15.6 0.13–0.17 OSSB-1 Concrete 84.5 20.0 0.28 4-10 STBR-3 Steel 52.2 15.9 0.11–0.36 4-11 STBR-2 Steel 82.0 9.1 0.13 4-12 STBR-4 Steel 106.2 44.9 0.124CBR-1 Concrete 152.6 50.2 0.29–0.59 Table 8. MASH estimated barrier load and friction (Bielenberg 2019; Pena et al. 2020; Rosenbaugh et al. 2021; Schmidt et al. 2009; Bielenberg, Faller, and Ronspies 2018).

Rigid Barrier Crash Data Analysis 41   However, weakly connected or flexible quarter panels may tear or disengage from the vehicle or engage a feature behind a barrier, which is not likely to increase occupant risk. Unfortunately, insufficient data were available to determine the force at which front quarter panels disengage from a vehicle. When these components engaged barriers, it was unclear if component stiffness was a result of engagement with the vehicle or entrapment with the bar- rier, and videos often cannot view the quarter panel-barrier interaction with enough detail to precisely identify snag risk and significant loads on features in the ZOI. The maximum lateral extent of the quarter panel over the barrier can be measured, but the capacity of a crushed, partially disengaged quarter panel was unknown, as was the case in test no. IBBR-2 (Bielenberg et al. 2020). 3.4.3 Suspension Joint Strength and Failure Time Vehicle suspension affects body ride height, center-of-mass and c.g. heights, vehicle stability, and barrier loading. Suspensions are designed to be stiff laterally, but flexible for vertical displace- ments through the wheel. Damage caused by wheel- and suspension-barrier loading affects vehicle-barrier interaction. Each test was reviewed to determine whether suspension failure or tire deflation occurred. The results are summarized in Appendix A, Table A-1. Even when reviewing highly detailed videos, it was difficult to definitively determine the time of and contributing factors to failure or deflation. Additionally, unless suspension component damage was detailed in the report, the components that failed (A-arm, tie rod, shock, etc.) usually could not be determined from photographs or videos. Suspension failure can be related to a stochasti- cally quasi-randomized event, such as wheel engagement and entrapment in wheel underride, wheel rim protrusion into an expansion gap, crack, or aesthetic feature, or camber failure from a protruding barrier toe. Nonetheless, suspension failure was observed for some impacts with continuous barrier faces. Based on the review of prior crash tests, vehicles that experienced impact-side wheel and suspension failure tended to have a trajectory that redirected back toward the barrier after exit- ing. If all wheels remained engaged, vehicle trajectory tended to be away from the barrier. Load applied through a vehicle’s wheel can increase vehicle roll toward the barrier, whereas load applied through the vehicle’s c.g. can cause more localized crushing and damage, quarter panel protrusion over the barrier-top surface, and increased overall vehicle damage. Modeling suspension failures with universally consistent failure criteria such as shear or bend- ing loads, moments, torque, or displacements for joint release often do not replicate test results. Modeling suspension release is sufficiently difficult that some laboratories, including MwRSF, use an impact time-based suspension failure parameter instead of load, stress, or equation- of-state techniques (Stolle, Reid, and Faller 2014). Therefore, several simulations are usually conducted to bracket possible outcomes with and without suspension failure. 3.4.4 Vehicle Properties MASH notes that vehicle mass and geometry critically affect vehicle interaction with road- side hardware, thus making it important to understand how these properties changed between NCHRP Report 350 and MASH testing standards (Ross et al. 1993; AASHTO 2016). Recommended properties, including masses and dimensions, of the 820C and 2000P passenger vehicles and the 8000S and 36000V vehicles used in NCHRP Report 350 crash testing of longi- tudinal barriers are summarized in Tables 9 and 10 (Ross et al. 1993). Weight recommendations for 820C, 2000P, 8000S, and 36000V test vehicles were 1,805 lb; 4,410 lb; 17,635 lb; and 80,000 lb, respectively.

42 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments Property Test Vehicle700C 820C 2000P Mass (kg) Test inertial 700 ± 25 820 ± 25 2,000 ± 45 Dummy 75 75 N/A Ballast (max.) 70 80 200 Gross static 775 ± 25 895 ± 25 2,000 ± 45 Dimensions (cm) Wheelbase 230 ± 10 230 ± 10 335 ± 25 Front overhang 75 ± 10 75 ± 10 80 ± 10 Overall length 370 ± 20 370 ± 20 535 ± 25 Track widthb 135 ± 10 135 ± 10 165 ± 15 Center of mass (cm)a Aft of front axle 80 ± 15 80 ± 15 140 ± 15 Above ground 55 ± 5 55 ± 5 70 ± 5 Location of engine Front Front Front Location of drive axle Front Front Rear Transmission Manual or automatic Manual or automatic Manual or automatic a For test inertial mass. b Average of front and rear axles. Table 9. NCHRP Report 350 recommended 820C and 2000P test vehicle properties (Ross et al. 1993). (Test Vehicle 700C was included in NCHRP Report 350 but not used in practice.) Property Test Vehicle 8000S 36000V/T a Tractorb Trailer Combination Mass (kg) Curb 5,450 ±450 N/A N/A 13,200 ± 1,400 Ballast As needed N/A Asneeded N/A Test inertial 8,000 ±200 N/A N/A 36,000 ± 500 Dimensions (cm) Wheelbase (max.) 535 480 N/A N/A Overall length (max.) 870 N/A 1,525 (V) N/A (T) 1985 Trailer overhangc N/A N/A 220 (V) 185 (T) N/A Cargo bed heightd 130 ± 5 N/A 132 ± 5 (V) N/A (T) N/A Center of mass (cm) Ballast 170 ± 5 N/A 185 ± 5 (V) 205 ± 10 (T) N/A Test inertial 125 ± 5 N/A N/A N/A a 36000V = 36,000-kg tractor-van trailer (TL-5); 36000T = 36,000 kg tractor-tank trailer (TL-6). b Tractor should be a cab-behind-engine model, not a cab-over-engine. c Distance from the rearmost part of the trailer to the center of the trailer tandem. d Without ballast. Table 10. NCHRP Report 350 recommended 8000S and 36000V/T test vehicle properties (Ross et al. 1993). The mass of all test vehicles increased with the adoption of MASH as the standard for roadside hardware crash testing, with the exception of the tractor-trailer, which remained the same. The NCHRP Report 350 pickup was replaced by a half-ton, quad cab, mid-size box pickup, and its weight increased by approximately 600 lb (AASHTO 2016). Recommended properties of each test vehicle used for MASH crash testing of longitudinal barriers are summarized in Tables 11 and 12. Recom- mended weights for 1100C, 2270P, 10000S, and 36000V test vehicles were 2,420; 5,000; 22,050; and 80,000 lb, respectively, with a minimum c.g. height of 28 in. for the pickup.

Rigid Barrier Crash Data Analysis 43   Table 12. MASH recommended 10000S and 36000V/T test vehicle properties (AASHTO 2016). Property Test Vehicle 10000S 36000V/T a Tractorb Trailer Combination Mass (kg) Curb 6,000 ±1,000 N/A N/A 13,200 ± 1,400 Ballast As needed N/A As needed N/A Test inertial 10,000 ±300 N/A N/A 36,000 ± 500 Dimensions (cm) Wheelbase (max.) 610 510 N/A N/A Overall length (max.) 1,000 N/A 1,615.5 (V) N/A (T) 1,985 Trailer overhang (max.)c N/A N/A 220 (V)185 (T) N/A Cargo bed heightd 124.5 ± 5 N/A 127 ± 5 (V) N/A (T) N/A 185 ± 5 (V) Ballast center-of-mass (cm) 160 ± 5 N/A N/A205 ± 10 (T) a 36000V = 36,000-kg tractor-van trailer (TL-5); 36000T = 36,000 kg tractor-tank trailer (TL-6). b Tractor should be a cab-behind-engine model, not a cab-over-engine. c Distance from the rearmost part of the trailer to the center of the trailer tandem. d Without ballast. Property Test Vehicle1100C 2270P Mass (kg) Test inertial 1,100 ± 25 2,270 ± 50 Dummy 75 Optionala Ballast (max.) 80 200 Gross static 1,175 ± 25 2,270 ± 50 Dimensions (cm) Wheelbase 250 ± 12.5 376 ± 30 Front overhang 90 ± 10 100 ± 7.5 Overall length 430 ± 20 602 ± 32.5 Overall width 165 ± 7.5 195 ± 5 Hood height 60 ± 10 110 ± 7.5 Track widthb 142.5 ± 5 170 ± 3.8 Center of mass (cm)c Aft of front axle 99 ± 10 157.5 ± 10 Above ground N/A 71 Location of engine Front Front Location of drive axle Front Rear Type of transmission Manual or automatic Manual or automatic a If used, increase gross static vehicle mass by dummy mass. b Average of front and rear axles. c For test inertial mass. Table 11. MASH recommended 1100C and 2270P test vehicle properties (AASHTO 2016).

44 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments In addition to vehicle dimension updates from NCHRP Report 350 to MASH, the exterior geom- etry of 1100C and 2270P test vehicles changed significantly, as shown in Figure 35. The exterior of the SUT and tractor-trailer trucks were similar under both testing standards. 3.4.5 Summary Interactions between test vehicles and rigid barriers were reviewed to develop preliminary estimates of vehicle- and tire-barrier friction values for use in simulation. Each full-scale crash test with suspension damage or tire deflation was recorded; no generalized contribution of forces, alignments, or wheel impact conditions were identified, which could be linked to wheel or sus- pension failure prediction. Based on the variability of suspension failure outcomes, researchers investigated several parameters that affected vehicle behavior during impact, including vehicle- barrier friction, quarter panel crush stiffness, suspension strength and failure time, and vehicle properties. Full-scale tests were used to identify preliminary, empirically based observations of ZOIs and provide calibration data for simulation models. During modeling, parameters were varied to evaluate the effects on predicted vehicle ZOI, including vehicle- and tire-barrier friction, suspension damage, and vehicle component connection strengths. Figure 35. NCHRP Report 350 (Ross et al. 1993) (top) and MASH passenger test vehicles (AASHTO 2016) (bottom).