CHAPTER 1

Introduction

1.1 Background and Problem Statement

Roadside safety features such as luminaire poles and sign supports have been subjected to crashworthiness evaluations using a variety of impact test specifications or guidelines. The current guidelines, outlined in the Manual for Assessing Safety Hardware (AASHTO 2016), provide guidance for evaluating breakaway luminaire poles, sign supports, and work-zone traffic control devices. To meet the requirements of Test Level 3 (TL-3), which is the most commonly used test level, three full-scale crash tests are necessary for each device. The FHWA currently requires that systems successfully complete the entire crash testing matrix to receive an FHWA eligibility letter.

Due to the many variations of luminaire poles, sign supports, and work-zone traffic control devices and the cost to certify them, MASH crashworthiness evaluations and product innovation have stagnated for some of these devices. Efforts under NCHRP Project 03-119 and NCHRP Project 22-43 have identified thousands of such devices and raised concerns about their crash safety performance. However, the requirement to conduct three full-scale crash tests for each device variation poses a significant burden for the FHWA, state departments of transportation (DOTs), and manufacturers of proprietary hardware. Highway agencies are faced with major workload and budget issues when trying to provide assurance that roadside devices meet safety requirements, all of which are complicated by limited inventories of such devices.

While NCHRP Project 03-119 investigated MASH compliance of the most prevalent roadside safety items within the three categories of sign supports, breakaway poles, and work-zone devices, NCHRP Project 22-43 was to determine whether families of systems can utilize a reduced test matrix for each design variation. To evaluate sign supports, breakaway luminaire poles, and work-zone traffic control devices to MASH standards while continually improving systems, it is desired to revise MASH with additional guidelines on selecting a critical test matrix for evaluating a family of devices.

NCHRP Project 22-43 has established a family of devices and developed testing protocols for the evaluation of each family defined within the three groups of sign supports, breakaway poles, and work-zone traffic control devices. For this study, the research team proposed organizing the systems into families within each of the three categories using a new definition for a “family of devices,” which was defined as follows:

A family of devices is a group of roadside safety devices that possess (1) at least one identical, critical, structural feature; and (2) possess a range of parameters that provide similar safety performance under MASH impact conditions.

Given the many critical features within each device category combined with the many variations in each device’s characteristics, this investigation would require an indefinite number

for defining the two families of systems could not be conducted with the available funds. Thus, the research team recommended the following two options for continuing the project:

1. Option 1: Complete One Family of Devices: Single 2¼-in., 12-Ga. PSST Sign Support. In Option 1, the research team proposed to focus on one family of devices that could be defined and analyzed with the remaining budget. The research team needed five to seven crash tests, depending on the test outcomes, to complete the project objectives for the noted PSST. The remaining budget was believed sufficient to evaluate the PSST sign support family.
2. Option 2: Continue with Two Families of Devices. In Option 2, the research team proposed to continue with both families of devices and conduct crash testing following the recommended plan in order of importance. As stated earlier, the remaining budget was not sufficient to conduct the full set of recommended crash tests to validate the two families of systems, and additional funds would be needed. Without running the full set of tests, the simulations (especially for the case of luminaire poles, which have limited existing crash tests) would not be fully validated and thus, the MASH testing guidelines for the two families may not have been fully defined. However, the full-scale crash tests (i.e., two tests on luminaire poles and four to five tests on the PSST sign support) would provide valuable information on the crashworthiness of both families under MASH impact conditions. Based on the simulation results and limited full-scale crash tests, findings would be provided for the studied cases under existing and modified MASH impact conditions. As best as possible, the research team would provide guidelines regarding the critical impact points, critical impact angles, and critical test matrices.

Following a review of the proposed recommendations, the panel decided that the research team should proceed with Option 2. Thus, the research team continued with two and five full-scale crash tests recommended for the families of the luminaire pole with TB1-17 transformer base and a single 2¼-in. by 12-ga. PSST sign support, respectively.

Data from these tests were used to validate or modify the LS-DYNA simulations, develop guidelines according to the approved outlines, and propose modifications to MASH. Finally, Interim Report No. 3 was assembled documenting all Phase III research efforts, and a research summary was presented at an in-person meeting between the research team and the panel members at the conclusion of Phase III. A breakdown of the individual tasks within Phase III is shown here:

• Task 10: Execute Testing Program
• Task 11: Validate Analytical Program
• Task 12: Develop Preliminary Guidelines and Propose Modifications to MASH
• Task 13: Develop Preliminary Examples to Demonstrate Proposed Modifications
• Task 14: Acceptance of Interim Report No. 3 and Panel Meeting

1.3.4 Phase IV

Upon the project panel’s approval of the Phase III interim report and draft guidelines, the draft guidelines were provided, and the final report was revised according to panel members’ comments. The panel members reviewed the final deliverables, and their comments were incorporated into the final deliverables. A breakdown of the individual tasks within Phase IV is shown here:

• Task 15: Revise Preliminary Guidelines
• Task 16: Acceptance of Final Deliverables

1.4 Report Organization

This report is organized as follows:

• Summary
• Chapter 1: Introduction
• Chapter 2: Testing Program: Breakaway Luminaire Poles
• Chapter 3: Validating Analytical Program: Breakaway Luminaire Poles
• Chapter 4: Testing Program: Breakaway Sign Supports, PSST Posts
• Chapter 5: Validating Analytical Program: Breakaway Sign Supports, PSST Posts
• Chapter 6: Investigation of Luminaire Pole and PSST Crash Tests and Simulations
• Chapter 7: Preliminary Draft Guidelines and Proposed Modifications to MASH
• Chapter 8: Summary and Conclusions
• References

The report also has several appendices that provide details related to the two families of devices studied under the project. These appendices can be found on the National Academies Press website (nap.nationalacademies.org) by searching for NCHRP Web-Only Document 405: Evaluating Crashworthiness of Sign Supports and Breakaway Luminaire Poles: Appendices.