The National Academies

NCHRP 22-40 [Active]

Update to AASHTO M 180-18 and Associated Highway Guardrail Specifications

  Project Data
Funds: $300,000
Staff Responsibility: Christopher McKenney
Research Agency: RoadSafe, LLC
Principal Investigator: Chuck Plaxico
Effective Date: 7/1/2019
Completion Date: 7/1/2021
Comments: Ongoing. This project was awarded continuation funds to study High Tension Cable Barriers.


Many states use AASHTO and ASTM standard specifications for their guardrail components. 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 standards can increase fabrication costs for hardware suppliers and ultimately transportation agencies. A manufacturer can spend a significant amount of resources matching one state’s standards only to start completely over to match another state’s standards. Consistency of specifications will 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 are not currently addressed by AASHTO M 180-18 are:
·       The asymmetrical W-Beam to thrie-beam transition section that has been in use for a number of years.
·       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 the 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. Research is needed to assure that transportation agencies are specifying and using correct materials in their highway guardrail systems.


The objectives of this research are to (a) perform a comprehensive review of AASHTO M 180-18 and its associated AASHTO and ASTM standards and (b) propose needed revisions to bring the specifications into conformance with current requirements and the state of practice for highway guardrail systems.

The revised standard shall specify—or make reference to standards for—materials for components of the highway guardrail system, including beams, posts, end terminals, connecting hardware, etc.

The proposed revisions and supporting commentary shall be provided to Technical Subcommittee 4d of the AASHTO Committee on Materials and Pavements (COMP TS 4d) and the AASHTO Technical Committee for Roadside Safety (TCRS) for review and possible adoption.


NCHRP 22-40 received continuation funding from AASHTO to add High Tension Cable Barriers to the Scope of Work. This document contains Appendices A and B



from the contractor’s final report on NCHRP Project 22-40. The main body of the final report, including Appendices C through D, has been published as NCHRP Research Report 1020: Investigation of Material Requirements for Highway Guardrail Systems.


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