Many states use AASHTO and American Society for Testing and Materials (ASTM) standard specifications for their guardrail components. However, changes to the state of practice and to guardrail materials have created a need to revise AASHTO Standard Specification M 180-18, Corrugated Sheet Steel Beams for Highway Guardrail, and its associated material standards, including those referenced in M 180-18.
A lack of consistent standard specifications can increase fabrication costs for hardware suppliers and ultimately transportation agencies. A manufacturer can spend a significant amount of resources matching one state’s standard specifications only to start completely over to match those of another state. Consistency of specifications can also help to increase competition, allowing for the possibility of lower hardware costs for transportation agencies.
Some examples of developments in materials and the state of practice for highway guardrail systems that were not currently addressed by AASHTO M 180-18 included:
- The asymmetrical W-Beam to thrie-beam transition section;
- Inconsistency in the material requirements for thrie-beam terminal transitions and connections;
- Use of high-strength steel bolts connecting thrie-beam terminal connectors to rigid barrier;
- Multiple slot patterns for thrie-beam terminal connectors, thrie-beam, and W-beam rails;
- Lack of consistent markings for components of the highway guardrail system;
- Changes to applicable locations and geometric equivalents for ASTM standard bolts;
- Use of multiple grades for steel posts;
- Lack of guidance for shop-bent W-beam or thrie-beam rails (e.g., longitudinal radius of curve, radius tolerances, marking of beam radius to aid maintenance, etc.);
- Lack of changes to the appropriate dimensions and tolerances (metric and inch) for holes in steel guardrails and posts;
- Lack of inclusion of anchor wire rope standards in AASHTO M 180-18;
- Lack of standards for swage fittings;
- Changes to bolt tolerance, shape, and torque requirements;
- Lack of paint and thermal spray specifications for guardrail beams and posts to meet the requirements for Type III guardrails;
- Implications of the greater longevity of painted weathering steels compared to ordinary carbon steels;
- Need for specifications for stainless steel beams, posts, and bolting to meet the requirements for Type IV guardrails;
- Recent years have seen an increased focus on the performance of roadside hardware. Therefore, research was needed to verify that transportation agencies are specifying and using correct materials in their highway guardrail systems.
Under NCHRP Project 22-40, “Update to AASHTO M 180-18 and Associated Highway Guardrail Specifications,” Roadsafe, LLC was asked to: (1) perform a comprehensive review of AASHTO M 180-18 and its associated AASHTO and ASTM standards; and (2) proposed language for consideration by AASHTO to incorporate the research results in the next update of the AASHTO M 180-18.