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

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118 6.1 Determination of ZOI Envelope Dimensions ZOI envelopes were plotted for each MASH test level and barrier height combination explored in Chapter  5. Researchers considered the RDG update recommended by NCHRP Research Report 972: Development of Safety Performance-Based Guidelines for the Roadside Design Guide (Ray, Carrigan, and Ray forthcoming) while preparing ZOI guidance. Because ZOI envelopes represent the possible extension of stiff vehicle components into a space located behind the barrier, conservative dimensions were utilized for the ZOI envelopes. It should be noted that vehicle component contact with fixed objects located in the ZOI may be acceptable but should be eval uated using full-scale crash testing and, potentially, simulation to confirm that occupant- risk evaluation criteria are not exceeded. The bounding dimensions utilized lateral ZOI envelope trends shown in Section 5.4, which were derived from maximum lateral extents from both test data and simulations for full-scale crash tests and simulations performed according to MASH impact conditions. For vertical extents, researchers reviewed test and simulation data and selected maximum limits of vertical displacement near the point of maximum lateral intrusion and estimated maximum reasonable bounds for vertical extents located at the barrier surface. When questions arose as to the accu- racy or repeatability of some test results that had unusual ZOI envelope characteristics, researchers applied their best judgment to evaluate the data. For example, in test no. TL5CMB-2, the test article was a 42-in.-tall, single-slope median barrier with head ejection recesses near the top of the barrier. This system resulted in significantly more trailer rotation than is typically observed in crash testing with other barriers of similar heights and single-slope geometries but without the head ejection recess. Therefore, the lateral extent from this barrier was considered, as it was reasonably consistent with other MASH TL-5 full-scale crash tests, but the vertical ZOI extent at the face of the barrier was not utilized in the ZOI envelope recommendations. Simulation data were used to estimate the bounds of the ZOI envelopes when test data were not available for comparison. Trends in simulation data were used to determine the most rep- resentative ZOI envelope estimate. A limited suite of computer simulations was performed, and recommendations for ZOI values were interpolated between known test data and simulation results. Interpolated and estimated values are italicized and shaded in gray in the recommenda- tions in the data tables for the figures in this chapter. A weak correlation was found between the barrier shape and ZOI envelope dimensions overall. For some vehicle-to-barrier configurations, the ZOI envelope behavior was consistently larger for one barrier shape than for the other two shapes evaluated but usually with less than 3 in. total separation between largest and smallest simulated ZOI values. Simulations reasonably captured the majority of measured ZOIs, but a few tests exceeded the maximum values identified in simulations. Test data varied more than simulation data, and no obvious trends were identified C H A P T E R 6 Recommended ZOI Envelopes

Recommended ZOI Envelopes 119   based on barrier geometry, which reflects differences in real vehicle construction, design, age, wear, and heights, whereas simulations do not have these statistical variations. In general, the largest simulated ZOI envelopes more accurately represented the extents recorded from full- scale tests. Recognizing that there is uncertainty in selecting the proper ZOI envelopes as well as uncertainty in real-world impact conditions, and in an attempt to ensure reasonable but still conservative ZOI envelopes, the ZOI envelope recommendations were not differentiated by barrier shape. All ZOI recommendations were based on maximum practical ZOI extents and linked to MASH test level and barrier height. The ZOI recommendations may be utilized in multiple ways. One conservative method of interpreting results is to extrapolate ZOI results for a barrier height based on the results of the next lowest barrier height shown in the table. For example, users may utilize ZOI envelope recom- mendations for a 45-in.-tall, single-slope barrier based on 42-in.-tall barrier recommendations for MASH TL-4 and TL-5 test conditions, and for a 44-in.-tall barrier for TL-3 test conditions. Alternatively, users may choose to interpolate between recommended values shown in the table based on barrier heights. Finally, a very conservative estimate for the ZOI envelope may utilize only points A and B for all barrier height and test conditions, which describe the maximum vertical and lateral extents of the ZOI windows, respectively (see A and B in the following figures). The trend lines for ZOI envelopes based on barrier height shown in Section 5.4 were used to determine the maximum lateral ZOI envelope extents for barrier heights ranging from the recommended lowest barrier height through 90 in. When ZOIs converged to zero, the height at which the ZOI became negligible was noted. Because ranges shown in the data were large, researchers divided barrier height ranges to provide additional discretization between known points of the ZOI envelopes. Data that were reinforced with simulation and/or full-scale crash test results were noted with unshaded cells and plain text, whereas recommended values based on interpolated estimates are shown in gray shaded cells with italic text. The resulting ZOI envelopes for each MASH test level are shown in the following sections. 6.2 MASH TL-2 Recommended MASH TL-2 ZOI envelopes are summarized in Figures 121 and 122. A detailed view of the recommended ZOI envelopes is shown in Figure 123. The ZOI envelopes were constructed from a lower rectangular portion and an upper sloped portion. For barriers of 42 in. or taller, however, the upper portion of the ZOI envelope collapsed, and a rectangular ZOI envelope was recommended. 6.3 MASH TL-3 Recommended MASH TL-3 ZOI envelopes are summarized in Figures 124 and 125. The ZOI envelopes were constructed from a lower rectangular portion and an upper sloped portion. For barriers of 42 in. or taller, however, the upper portion of the ZOI envelope collapsed, and a rectangular ZOI envelope was recommended. For a comparison of recommended ZOI envelopes for MASH TL-3 impact conditions for all barrier heights, see Figure 126. 6.4 MASH TL-4 Recommended MASH TL-4 cab ZOI envelopes are summarized in Figure 127. Due to the risk of occupant injury from cab extension into the ZOI envelope, a conservative, rectangular cab zone was used for all heights for which the cab zone ZOI was nonzero. Recommended box zones are shown in Figures 128 and 129. For barrier heights up to 48 in. tall, the bottom edge of the box extended over the top surface of the barrier, and five-point ZOI envelopes were recommended.

120 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments Barrier-Top Height (in.) Dimension (in.) A B C D 24 76 16.0 7.5 57 27 65 14.6 7.5 54 29 64 13.6 7.5 54 32 64 12.1 7.5 54 36 61 10.2 5.4 54 39 61 8.8 5.4 54 NOTE: Cells noted in unshaded cells represent values from simulation and/or full-scale testing. Italicized values shown in gray were interpolated based on data trend lines. Figure 121. MASH TL-2 ZOI recommended envelope dimensions: heights less than 42 in. Barrier-Top Height (in.) Dimension (in.) A B 42 58 7.3 46 58 4.9 50 58 2.5 54 55 0.0 NOTE: Cells noted in unshaded cells represent values from simulation and/or full-scale testing. Italicized values shown in gray were interpolated based on data trend lines. Figure 122. MASH TL-2 ZOI recommended envelope dimensions: heights 42 in. or taller. Figure 123. Comparison view of recommended ZOI envelopes: MASH TL-2 impact conditions.

Recommended ZOI Envelopes 121   Barrier-Top Height (in.) Dimension (in.) A B C D 29 77 18.0 7 61 32 77 18.0 5 61 34 74 18.0 4 61 36 71 18.0 3 61 38 68 16.9 2 61 40 65 14.4 1 61 NOTE: Cells noted in unshaded cells represent values from simulation and/or full-scale testing. Italicized values shown in gray were interpolated based on data trend lines. Figure 124. MASH TL-3 ZOI dimensions, barrier heights less than 42 in. Barrier-Top Height (in.) Dimension (in.) A B 42 61 12.0 44 61 9.4 46 61 6.8 48 61 4.3 50 61 3.2 52 58 2.0 54 58 0.8 NOTE: Cells noted in unshaded cells represent values from simulation and/or full-scale testing. Italicized values shown in gray were interpolated based on data trend lines. Figure 125. MASH TL-3 ZOI dimensions, barrier heights 42 in. or taller. Figure 126. Comparison view of recommended ZOI envelopes: MASH TL-3 impact conditions.

122 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments For barrier heights greater than or equal to 48 in. tall, the box leaned over the top edge of the barrier into the ZOI envelope, and the ZOI envelope only contained an upper zone. For a comparison of recommended cab and box ZOI envelopes for MASH TL-4 impact conditions, see Figures 130 and 131, respectively. 6.5 MASH TL-5 Recommended MASH TL-5 cab ZOI envelopes are summarized in Figure 132. Due to the risk of occupant injury from the cab extension into the ZOI envelope, a conservative, rectangular cab zone was used for all heights for which the cab zone ZOI was nonzero. The recommended trailer ZOI envelopes are shown in Figures 133 and 134. For barrier heights up to 62 in. tall, the bottom edge of the trailer extended over the top surface of the barrier, and five-point ZOI envelopes were recommended. For barrier heights greater than or equal to 54 in. tall, the trailer leaned over the top edge of the barrier into the ZOI envelope, and the ZOI envelope only contained an upper zone. Note that anecdotal test data suggest that the transition between the trailer sliding on top of the barrier versus contacting the front face may be closer to 48 in. than 54 in. For a comparison of recommended cab and trailer ZOI envelopes for MASH TL-5 impact conditions, see Figures 135 and 136, respectively. 6.6 Discussion The ZOI envelopes presented in this report represent the culmination of full-scale crash test data and calibrated, validated computer simulations used to explore barrier configurations for which test data do not already exist. In general, the ZOI envelopes were intended to capture Barrier-Top Height (in.) Dimension (in.) A B 36 115 36.0 42 111 24.0 46 111 8.5 48 N/A 0.0 NOTE: Cells noted in unshaded cells represent values from simulation and/or full-scale testing. Italicized values shown in gray were interpolated based on data trend lines. Figure 127. MASH TL-4 cab ZOI dimensions.

Recommended ZOI Envelopes 123   Barrier-Top Height (in.) Dimension (in.) A B C D E F 36 181 88 148 89 27.0 30 42 181 63 146 103 36.5 24 Figure 128. MASH TL-4 box ZOI dimensions: barrier heights less than 48 in.

124 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments NOTE: Cells noted in unshaded cells represent values from simulation and/or full-scale testing. Italicized values shown in gray were interpolated based on data trend lines. Barrier-Top Height (in.) Dimension (in.) A B C D E 48 137.5 32.0 13.5 130 117 64 137.5 25.0 13.5 129 117 76 136.0 20.0 13.5 129 116 90 135.0 13.5 5.0 129 116 Figure 129. MASH TL-4 box ZOI dimensions: barrier heights 48 in. or taller.

Recommended ZOI Envelopes 125   the maximum extent of stiff vehicle component intrusion beyond the top, traffic-side edge of rigid barriers. For some results, measurements were deemed outliers, primarily due to the unique configurations or geometries of the barrier systems (e.g., a vertical taper, transition ele- ments, etc.). Thus, while recommendations are conservative, there are specific configurations not addressed in these guidelines for which additional consideration may be warranted. Conservative guidelines were recommended because vehicle components extending into the ZOI indicate there is potential that a stiff vehicle component could engage with a structure located behind or above the barrier system. In some events, such contact could increase occu- pant risk, impose vehicle damage, or damage a structure located behind a barrier system. How- ever, multiple successful, full-scale crash tests have been conducted in which vehicles engage features located in the ZOI, as noted in Chapter 2. Roadside structures located within the ZOI should be evaluated to determine whether the combination of barrier and structure are crash- worthy, whereas vehicles are unlikely to contact structures located outside of the ZOI envelope during a crash. The ZOI envelopes were intended to reflect practical, maximum extension of vehicle compo- nents tested under MASH criteria but may not capture extreme events. For example, based on a video of test no. 469468-2-1, performed at TTI, it appears that the trailer experienced cata- strophic connection damage, and the truck trailer’s fifth-wheel connection failed during the test, resulting in box disengagement from the truck. A sequential image from the test is shown in Figure 137. Furthermore, unique circumstances—including aftermarket components added to vehicles—or roadway slopes and geometrics could lead to actual component intrusions exceed- ing the recommended envelopes. Figure 130. Comparison view of recommended cab ZOI envelopes: MASH TL-4 impact conditions.

126 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments Figure 131. Comparison view of recommended box ZOI envelopes: MASH TL-4 impact conditions.

Recommended ZOI Envelopes 127   Barrier-Top Height (in.) Dimension (in.) A B 42 113.5 21.5 48 108.5 15.5 54 107.0 9.5 62 N/A 0.0 Figure 132. MASH TL-5 cab ZOI dimensions. Barrier-Top Height (in.) Dimension (in.) A B C D E F 42 185.0 85 153 98 33 70 48 157.5 35 153 128 48 12 Figure 133. MASH TL-5 trailer ZOI dimensions: barrier heights less than 54 in.

128 Zone of Intrusion Envelopes Under MASH Impact Conditions for Rigid Barrier Attachments Barrier-Top Height (in.) Dimension (in.) A B C D E 54 156 32.5 21.0 153 128 62 156 29.5 21.0 153 128 72 156 25.5 18.0 153 132 84 156 20.5 13.0 152 140 90 156 18.0 10.5 152 144 NOTE: Cells noted in unshaded cells represent values from simulation and/or full-scale testing. Italicized values shown in gray were interpolated based on data trend lines. Figure 134. MASH TL-5 trailer ZOI dimensions: barrier heights 54 in. or taller. Figure 135. Comparison view of recommended cab ZOI envelopes: MASH TL-5 impact conditions.

Recommended ZOI Envelopes 129   Figure 136. Comparison view of recommended trailer ZOI envelopes: MASH TL-5 impact conditions. Figure 137. Sequential image at end of test no. 469468-2-1 indicating trailer damage.