CHAPTER 7

Preliminary Draft Guidelines and Proposed Modifications to MASH

A total of two full-scale crash tests were conducted on steel luminaire poles supported on the TB1-17 transformer base, while five tests were carried out on 2¼-in. × 2¼-in. 12-gauge PSST posts. After the full-scale crash testing, the LS-DYNA simulations were validated using the new test data, leading to substantial improvements in the accuracy of predicting the impact behavior of these devices. However, the validation process is incomplete without running the full set of tests. For instance, the simulations for luminaire poles representing MASH Test Nos. 3-61 and 3-62 impact conditions lack full-scale crash test data for validation, and the outcomes for the PSST post testing were not consistent, which makes it challenging to develop guidelines and suggest modifications to MASH for these systems. Thus, the concept of identifying a family and utilizing a reduced test matrix to determine crashworthiness could not be fully demonstrated.

However, despite these challenges, the research team closely analyzed all available crash test data along with the simulation results. This comprehensive analysis has enabled the research team to identify several trends. If these trends are confirmed through future full-scale crash testing, they will reduce the necessary testing matrices. Such validation would ensure that critical impact conditions are evaluated. Final recommendations to reduce testing matrices require future full-scale crash tests and evaluation of impact conditions to confirm these trends. It is important to note that the information from this study cannot be immediately applied but serves as a foundation for future research and potential enhancements in the development of guidelines and MASH modifications.

7.1 Luminaire Poles Supported by TB1-17 Transformer Base

This section first details the trends that have been identified based on hundreds of simulations and a limited number of full-scale crash tests. Next, a preliminary categorization of luminaire poles based on their heights and weights is introduced, which provides a framework for evaluating luminaire poles with the requisite tests under critical impact conditions. It is important to emphasize that this categorization is not immediately applicable until the subsequent steps detailed in the following sections are undertaken.

If the guidelines suggested based on this research are confirmed and validated through future full-scale crash testing and simulation, they can be incorporated into MASH. It is worth noting that, depending on the final results, these guidelines may not necessarily reduce the number of tests for some pole configurations. Instead, three tests may be suggested for a particular category of poles with more realistic critical impact conditions in those tests.

7.1.1 Draft Guideline for Evaluation of Luminaire Poles with TB1-17 Transformer Base

In this project, 39 steel pole configurations covering a full range of design parameters (e.g., pole height ranging from 20 ft to 50 ft, mast arm length ranging from 4 ft to 30 ft with single and dual mast arms) were simulated under MASH Test Nos. 3-60, 3-61, and 3-62. For each test designation, the impact point on the vehicle varied between the center point and left- and right-quarter points of the test vehicles.

While the luminaire pole simulation results have not been fully validated against full-scale crash tests, some trends have been observed in the simulated crash performance of various pole configurations under different MASH test matrices. These trends in evaluation criteria and critical impact conditions are as follows:

• None of the simulations (MASH 3-60, 3-61, and 3-62) or full-scale crash tests resulted in ORA values (lateral and longitudinal) or roll or pitch values exceeding the MASH maximum limits.
• Considering the current MASH criteria, the simulations and full-scale crash tests have shown that the following measures are critical in evaluating luminaire poles:
  • Pole base must break away upon impact.
  • Longitudinal OIV should not exceed 16 ft/s.
  • Maximum intrusion into occupant compartment should be less than MASH limits (i.e., 4 in. for roof crush, 3 in. for windshield and rear window).
  • No part of the luminaire should penetrate the vehicle’s interior occupant compartment.

MASH Test No. 3-60 Impact Trends

• MASH Test No. 3-60 impact conditions tended to be more critical than those for MASH Test Nos. 3-61 and 3-62 in terms of roof crush. In low-speed impacts, the likelihood of the pole falling on the vehicle’s roof or windshield increases as compared to during high-speed impacts.
• In MASH 3-60 impacts, for the majority of pole configurations, center impacts were identified as more critical than right- or left-quarter point impacts in terms of roof crush. This finding is due to the propensity for the pole to fall longitudinally and land directly on the vehicle instead of being pushed to the side of the vehicle during quarter-point impacts. The center of the vehicle’s roof also tended to be less stiff as compared to the roof sides, which resulted in larger roof deformations under pole impacts.
• While there are instances where a 25-degree impact angle resulted in increased roof crush as compared to 0-degree impact angle, the general trend indicates that a center impact point was more likely to lead to pole contact with the center of the roof, thereby causing higher roof crush.
• Excluding one outlier, the simulations showed that the roof crush concern appears for poles weighing more than 500 lb. The short and light poles showed less roof crush as compared to the heavy poles (if the pole falls on the vehicle’s roof).
• Given the presence of roof crush concerns for all pole configurations, under MASH 3-60 with a center impact point and 0-degree impact point, where all pole configurations showed a medium or low potential of passing MASH roof crush criteria (Table 34), it is necessary to conduct one full-scale crash test on any pole configuration. This test will ensure evaluation of the pole performance under this critical impact condition.
• Note that there is still a possibility that the pole may fall onto the side of the vehicle and thus pass the roof crush criterion. This outcome can be due to the inherent variability in base fracture behavior and the inconsistencies in pole response during impacts.

• In MASH 3-60 impacts, in several cases, mostly associated with left- or right-quarter impact points at a 25-degree angle, the base did not break away (indicated as “NB” in Table 34), and significantly high OIVs were observed. For these impact conditions, a distinct behavior was observed as the small car began to yaw and rotate around the base, preventing it from breaking away. The research team believes this behavior could be attributed to the modifications added to the base, as shown in Figure 56. These modifications resulted in the reinforcement of the base, making it stronger and stiffer at the corners. Such observation needs to be validated through full-scale crash testing under this impact condition (i.e., left- or right-quarter impact point with 25-degree impact angle). This impact condition resulted in an OIV higher than other impact conditions for MASH 3-60 impacts across all pole configurations, even short and light poles. If this is validated, for all pole configurations, at least one full-scale crash testing is essential under MASH 3-60 with a left-/right-quarter impact point to evaluate OIV criterion.
• In summary, for MASH 3-60 impacts, the center impact point with a 0-degree impact angle tended to result in higher roof crush, while the left-/right-quarter impact points with a 25-degree impact angle led to higher OIV, even exceeding those observed in MASH 3-61 impacts.

MASH Test No. 3-61 Impact Trends

• None of the MASH 3-61 impacts resulted in vehicle contact with the pole or any intrusion of the pole into the occupant compartment.
• There was a noticeable trend of increased OIV values as the total weight of the systems increased.
• In MASH 3-61 impacts, OIVs begin to raise concerns for heavy poles, specifically those weighing more than 800 lb. Note that the determination of critical pole specifics, such as height or weight thresholds, requires MASH 3-61 full-scale crash testing to provide definitive validation. These tests are needed for confirming and refining the criteria used to evaluate luminaire poles. OIV values for a majority of tall and heavy poles (heavier than 800 lb) exceed the MASH limit. Thus, it is recommended to conduct one MASH 3-61 full-scale crash test on medium-weight and tall/heavy poles to evaluate OIV.
• The center impact point at a 0-degree angle showed OIV values that were either similar to or higher than those observed in other impact conditions, such as the 25-degree angle, left-quarter, and right-quarter impacts. As such, center impact at a 0-degree impact angle and center impact point scenario can be considered a suitable representative for assessing OIV in MASH 3-61 tests.

MASH Test No. 3-62 Impact Trends

• In MASH Test No. 3-62, for all simulated cases ranging from short and light poles to tall and heavy poles, OIVs were less than those resulting from MASH Test No. 3-61 impacts. Thus, luminaire poles need to be evaluated under MASH Test No. 3-61 to ensure OIVs will meet MASH criteria.
• None of MASH 3-62 impacts resulted in vehicle contact with the pole or any intrusion into the occupant compartment.
• These observations, once validated through full-scale crash testing, suggest that there may be no need to conduct pickup truck tests on any pole configuration.
• The simulation results indicated that as the impact speed is lowered to around 30 mph for short poles and around 40 mph for tall poles, pole contact with the pickup truck starts to occur. It is important to note that low-speed pickup truck tests are not currently included in the existing MASH standards. Further research is required to investigate the necessity of such impact conditions and to compare their criticality with MASH 3-60 or MASH 3-61 tests. The focus will be on understanding whether a pole that passes MASH 3-60 and/or MASH 3-61 is likely to also pass low-speed pickup truck tests, which will help inform future safety standards and testing requirements.

Based on the comprehensive simulation results and the available full-scale crash test data, a preliminary set of recommendations has been compiled for the required crash tests to evaluate various pole configurations, as shown in Table 44.

For short poles, those measuring less than 20 ft in height and weighing a maximum of 450 lb, two tests are recommended:

• One MASH 3-60 with a center impact point and a 0-degree impact angle for roof crush evaluation.
• One MASH 3-60 test with a left-/right-quarter impact point and a 25-degree impact angle for OIV evaluation.

Note that the necessity for the latter test, which is intended for OIV evaluation, should be confirmed through full-scale crash testing with a 25-degree impact angle. Currently, there is no 25-degree test available to provide a definitive statement. However, based on simulations, it is evident that this specific impact condition at the left/right quarter results in higher OIV values compared to other impact conditions, indicating the need for further validation.

For medium-height poles, those measuring above 20 ft and less than 40 ft and weighing a maximum of 800 lb, two tests are similarly recommended:

• One MASH 3-60 with a center impact point and a 0-degree impact angle for roof crush evaluation.
• One MASH 3-60 test with a left-/right-quarter impact point and a 25-degree impact angle for OIV evaluation.

For tall and heavy poles, those measuring above 40 ft and weighing above 800 lb, three tests are recommended:

• One MASH 3-60 with a center impact point and a 0-degree impact angle for roof crush evaluation.
• One MASH 3-60 test with a left-/right-quarter impact point and a 25-degree impact angle for OIV evaluation.
• One MASH 3-61 with center impact point and 0-degree impact angle for OIV evaluation.

Upon validation of these recommendations, the number of required tests for evaluating the majority of luminaire poles is anticipated to be reduced to two tests, and potentially even one test depending on the results of full-scale crash testing with a 25-degree impact angle.

For tall and heavy poles, the requirement for three full-scale crash tests remains, but these three tests differ from the current MASH recommendations. Critical impact conditions have been identified and recommended based on the specific characteristics and behavior of these pole configurations. This refined approach ensures a more targeted and relevant assessment of pole performance in critical scenarios.

In the following section, the steps required to validate the recommendations are provided.

7.1.2 Next Steps Required to Validate Guidelines

To validate the recommendations presented in Table 44 and to further refine the pole categories (i.e., family of devices), a series of full-scale crash tests are necessary. These tests will also provide data for future simulation validation.

For short poles, no specific concern for OIV was observed except in the case of the right-quarter impact point and 25-degree impact angle. The research team believes that if such impact conditions show OIV concerns for medium or tall poles, similar concerns may exist for short poles due to the similarities observed in simulation results. Thus, these specific impact conditions will be crash tested only for medium and tall poles. For short poles, only roof crush will be evaluated under the center impact point and 0-degree impact angle. Available full-scale crash tests and simulations indicate that there should not be a concern for roof crush for short and light poles. The lightest pole that caused a roof crush above 4 in. had a weight of 553 lb (Test No. 440862-01-2, conducted at TTI).

For medium poles, two MASH 3-60 tests are needed: one with a center impact point and a 0-degree impact angle for roof crush evaluation and one with a left-/right-quarter impact point for OIV evaluation. Additionally, one MASH 3-61 test is needed for OIV evaluation. There have been cases in this category that showed OIV values close to the threshold of 16 ft/s.

For tall and heavy poles, three tests are needed: one MASH 3-60 test with a left-/right-quarter impact point for OIV evaluation, one MASH 3-61 test, and one MASH 3-62 test with a center impact point and a 0-degree impact angle for OIV evaluation.

For each category, the most critical pole configurations should be selected for testing. In total, a minimum of seven tests will be required to validate the recommendations and refine the pole categories, as shown in Table 45.

7.2 Breakaway Sign Supports – PSST Posts

The results from a matrix of simulations and full-scale crash tests were analyzed to develop preliminary guidelines for testing a family of small-sign support systems and suggest updates to the current MASH 2016 test matrix. The guidelines developed are based on analyses performed on one family of small-sign support systems, specifically the PSST system with 2¼-in. × 2¼-in. × 12-gauge posts. Additionally, a limited number of crash tests were conducted on this family of devices. Therefore, further analyses and testing of the PSST system (with different post sizes, panel base heights, and so forth) and other systems (e.g., cylindrical posts, U-shaped posts) are needed before finalizing the guidelines. The following sections will outline some of the findings and the suggested guidelines.

7.2.1 Test Matrices

A matrix of tests is currently defined in MASH for sign support systems. Running this matrix for all possible configurations of a family of PSST systems would be cost-prohibitive. Using the simulation analyses that were performed to identify the effects of different impact and design configuration parameters and the full-scale crash test results, a preliminary matrix of tests was developed to reduce the number of required tests without compromising the evaluation and safety of the different configurations within the PSST family of devices. Table 46 depicts the suggested updated test matrix for small-sign support systems. Only Test Level 3 is included in the table, but similar tests can be adopted for the other test levels. The impact speeds, test vehicles, and evaluation criteria were kept unchanged from the original MASH recommendations. Impact angles and impact locations were updated to reflect the worst-case scenario. Based on the preliminary matrix, a minimum of six tests are needed for each family of devices, with two additional tests required based on the outcome of the first six tests. Justifications for the selection of tests and updated impact conditions are included in the following sections.

7.2.2 MASH Test No. 3-60A Impact

As previously mentioned, Test 3-60 was the least critical of the three impacts for the family of the PSST sign support system considered. All cases for this impact were found to meet all

MASH criteria. The sign system in these cases was bent at the ground level and did not separate from the anchoring sleeve. The sign system continued to bend, went under the vehicle, and did not contact the vehicle’s windshield or roof. The only critical parameter for these cases was found to be the OIV; however, while the OIV increased with increased panel size, even with the largest panel size the OIV was below the critical MASH number. Based on these findings, only one test with the largest sign panel is included in the suggested preliminary test matrix.

7.2.3 MASH Test No. 3-61A, 3-61B, and 3-61C Impacts

MASH Test No. 3-61 is the most critical of the three tests for this PSST family of devices. It was noted that the size of the panel affects the MASH performance outcome. Small and medium-sized panels were sometimes more critical than larger sizes. Based on these findings, tests with the largest (3-61A) and smallest (3-61B) sign would need to be performed, and based on the outcome, an additional test with midsize sign (3-61C) would need to be performed if the sign does not impact the same region of the vehicle (e.g., if the smallest panel hit the hood and the larger panel hit the roof, a test with a size in between would be needed). Typically, the shortest configuration would have the lightest weight, and the tallest configuration would be the heaviest. If more than one of the configurations had the same height, the heaviest of all configurations with the same height (for the shortest, tallest, or mid-height) would need to be selected for the test unless there would be evidence that lighter systems would have more critical performance.

7.2.4 MASH Test No. 3-62A, 3-62B, and 3-62C Impacts

Similar effects were noted for MASH Test No. 3-62. The panel size affects the MASH performance, and the middle panel size could be more critical than the smallest and largest sizes. Tests with the largest (3-62A) and smallest (3-62B) sign would need to be performed, and based on the outcome, an additional test with midsize sign (3-62C) would need to be performed if the sign did not impact the same region of the vehicle (e.g., if the smallest panel hit the hood and the larger panel hit the roof, a test with a size in between would be needed).

7.2.5 Selection of Critical Impact Point

Simulations at different impact locations were incorporated into the matrix of simulations to investigate their effects on the MASH performance of the system. Three impact locations were incorporated in the simulations: a center impact where the centerline of the vehicle was aligned with the signpost, a quarter-vehicle width offset toward the driver’s side (+¼ w), and quarter-vehicle width offset toward the passenger side (−¼ w).

The results showed significant differences between the behavior of center and offset impacts. In the offset impact cases, the posts sheared or separated from the base much sooner than in the center impact. This is attributed to the fact that the offset region of the vehicle is stiffer than the center region, leading to higher forces applied on the post and quicker failure/release. This caused the behavior of the offset impacts to be more critical for shorter signs as the quicker release led to increased likelihood of impacting the windshield. The center impact, on the other hand, was found to be more critical for taller signs as the delayed release increased the chances of the panel impacting the windshield. The simulations indicated that there was no significant difference between the +¼ w offset case (offset toward the driver’s side) and the −¼ w offset case (toward the passenger). Based on these findings, offset impacts were selected for shorter signs, and center impacts were selected for the taller signs.

7.2.6 Selection of Critical Impact Angle

Configurations at different impact angles were incorporated into the matrix of simulations to investigate the effects of the angle on system performance. Impacts at 0 degrees, −25 degrees (sign rotated clockwise relative to the upward vertical axis), and +25 degrees (counterclockwise) were used in simulations based on MASH guidelines.

In most PSST sign support system cases that were analyzed, similar behavior was observed between the 0-, −25-, and +25-degree impact angle cases. In some instances, the +25- and −25-degree cases were more likely to contact the windshield than the 0-degree case. This is attributed to the fact that at 25 degrees, the edge of the panel is closer to the vehicle/windshield than at 0 degrees. It was therefore recommended that the 25-degree impact be adopted in the test matrix. For center impacts, the sign panel edge would be the same distance from the windshield for +25- and −25-degree angles; hence, either can be used. For offset impacts, the +25 (counterclockwise rotation) would be more critical than the −25 (counterclockwise) if the offset is toward the driver side, and −25 would be more critical if the offset is toward the passenger side. Based on these observations, the 25-degree impact was selected for the test matrix. Figure 156 shows the critical impact angle and location for the center (3-61A, 3-62A) and offset (3-60A, 3-61B, 3-61C, 3-62B, 3-62C) impacts.

It is important to note that, even though some recent testing has been performed at a 90-degree impact angle, there is still a debate on whether this angle would be run for high-speed (TL-3) impacts. It is stated in MASH that “features that are designed to be used along the outside of divided highways need only be evaluated for impact angles of 0 to 25 degrees” (AASHTO 2016). The 90-degree impact would be applicable for systems that are designed to be installed at intersections where the speed is lower; therefore, the 90-degree impact angle was not considered in this study. Based on recent testing results, 90-degree impacts may be more critical than the 25-degree impacts; hence, further investigation is needed to develop more understanding of these scenarios.

7.2.7 Next Steps Recommended to Define Family of Devices

The guideline development was based on a series of analyses conducted on a specific family of small-sign support systems. This family is characterized by the PSST system, which utilizes posts measuring 2¼-in. by 2¼-in. and is made from 12-gauge material.

To supplement these analyses, a select number of crash tests were also carried out on this specific family of devices. These tests provided valuable insight into the real-world performance and reliability of the systems under study.

Leveraging the data from simulations, insights obtained through full-scale crash tests, and existing literature, the research team formulated a matrix for conducting MASH tests on a family of PSST sign support systems. Instead of executing the three impacts (3-60, 3-61, and 3-62) for each configuration within the device family, the preliminary updated matrix includes fewer critical tests on select configurations. This streamlined approach reduces the number of required tests while ensuring the thorough evaluation and safety of all configurations within the PSST family of devices. Table 46 illustrates the preliminary updated test matrix for the analyzed PSST systems, primarily focusing on Test Level 3. Similar test adaptations can be made for other levels, and the same table can be applied to other small-sign support systems following additional analyses and testing.

It is important to note that the test matrix developed in this study was validated through computer simulations and testing for PSST sign support systems with one specific configuration (namely a 2¼-in. PSST post). There are other variations within the PSST systems, such as different post sizes and panel base heights, that have yet to be explored. Additional analyses and testing would be needed to verify that this matrix is valid for these other configurations.

Moreover, there are also other types of systems, such as those using cylindrical posts or U-shaped posts, that need to be investigated. Additional analyses and testing of these systems are crucial in order to develop more comprehensive and robust guidelines for all small-sign support systems.

Therefore, before the recommended test matrix can be finalized, further analyses and testing are needed. This will ensure that the guidelines are not only based on an understanding of one specific system but also take into account the diverse range of systems that are used in practice.