The National Academies

NCHRP 24-50 [Active]

Rewrite of the AASHTO Drainage Manual

  Project Data
Funds: $600,000
Staff Responsibility: Roberto Barcena
Research Agency: Ayres Associates
Principal Investigator: James Schall
Effective Date: 8/9/2021
Completion Date: 8/9/2024
Comments: Research in progress


The AASHTO Drainage Manual (ADM 2014 version) provides state departments of transportation (DOTs) with a template and baseline for the development of highway drainage design manuals. The ADM provides default guidelines in the absence of a state DOT drainage manual for federally funded projects. Historically, the ADM is written in such a way that an agency can adopt and implement it with their specific design criteria that reflect their specific policies, saving significant time and resources. Since the original publication in the 1970s, many state DOT drainage design manuals have been developed based on the information and cumulative experience represented by this document and its subsequent editions. It is a publication that reflects the best knowledge and experience of several generations of highway hydraulic engineers.

The 15-chapter, 1157-page AASHTO Highway Drainage Guidelines (HDG) parallels the ADM in many ways, but the use and purpose of the two documents are distinctly different. The HDG provides guidance on hydraulic design considerations that should be made during planning and design of highway drainage facilities. The ADM provides a template for development of a state specific drainage manual with policy, criteria, and design procedures (including example problems).

Discussion between the AASHTO Technical Committee on Hydrology and Hydraulics (TCHH) and the research team for NCHRP Project 20-07 (417), “Reorganization and Strategy to Update the AASHTO Drainage Manual” suggested a strong preference for merging the two volumes of the ADM into a single volume and archiving the current edition of the HDG. The TCHH indicated a preference to rename the combined document as the AASHTO Hydraulics and Water Resources Manual (AHWRM) focused on policy and design criteria with references to FHWA hydraulic publications for supplemental technical information when appropriate. The AHWRM should also include fundamental water resource concepts to ensure a sound rationale for the policy and design criteria.


The objective of this research is to produce a new, up to date AHWRM informed by the 2014 ADM and the results of NCHRP Project 20-07(417) that provides state DOTs and local transportation agencies with design policy and guidance and the technical background required to support them.

The new AHWRM shall be in the format of modules that enables faster implementation and future updates to incorporate future research findings, emerging issues and technologies, and new design responsibilities. Further, the new manual shall incorporate any material from the HDG that is identified as appropriate for inclusion. The manual shall be a primary reference for policy, design criteria, design procedures, and emerging technologies for the state DOTs and local agencies. It shall further provide a broader perspective than that found in the state DOTs’ manuals and deeper technical resources.

The research shall explore multiple formats for the written text focused on enhancing the readability, comprehension, and ease of use and revision of the text.

Status: Research is in progress.

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