Written and maintained by CASRAI Editorial Board
Last updated
Short answer
The AASHTO Green Book is the common name for A Policy on Geometric Design of Highways and Streets, published by the American Association of State Highway and Transportation Officials (AASHTO). The 7th edition (2018) is the current published edition, and it is the edition named in the federal regulation 23 CFR 625.4(d)(1)(i) (eCFR version dated 2026-11-01). It is a design policy for road geometry, not a laboratory test method.
What the AASHTO Green Book is
AASHTO describes the Green Book as the pre-eminent industry guide to current highway and street design research and practices (AASHTO Journal, 28 September 2018). Its subject is geometric design: the dimensions and layout of a roadway, as opposed to its structural pavement design or the materials tests used to build it.
The 7th edition was described by AASHTO at release as more flexible, multimodal and performance-based than its predecessors. Its first chapter, “New Framework for Geometric Design”, introduces that approach.
How the Green Book is used in practice
Functional class and context class
The 7th edition pairs the long-standing functional classes of roads with a new set of context classes:
| Classification | Categories named by AASHTO |
|---|---|
| Functional class | Local, collector, arterial, freeway |
| Context class | Rural, rural town, suburban, urban, urban core |
Designing for both the role a road plays in the network and the setting it sits in is what AASHTO means by a more flexible, performance-based framework: a design value is chosen for the situation, not read from a single table.
Project types
The 2018 introduction names the kinds of projects the book addresses: new construction, reconstruction, and projects on existing roads. An agency applying the book to an existing road is therefore working from the same policy used for new alignments, with judgment applied to the constraints of the site.
Edition history and federal status
The federal status of the book is the part most summaries leave out, and it matters when deciding which edition governs a project.
- 2011 (6th edition). Before the 2018 release, 23 CFR Part 625 incorporated the 2011 edition for projects on the National Highway System (NHS).
- September 2018 (7th edition). AASHTO published the 7th edition, often called the 2018 Green Book.
- 10 May 2019, FHWA memo HICP-10. The Federal Highway Administration (FHWA) stated that, until rulemaking, the 2018 edition was guidance. FHWA found the updates met or improved the 2011 criteria, so a state DOT could adopt the 2018 edition for NHS projects without processing a formal design exception. Off the NHS, states kept their own discretion. The memo is marked Archived on the FHWA site.
- Current regulation. The eCFR version of 2026-11-01 lists “AASHTO GDHS-7, A Policy on Geometric Design of Highways and Streets, 7th Edition, 2018” in 23 CFR 625.4(d)(1)(i), incorporated by reference. The regulation now names the 7th edition itself.
Is there an 8th edition?
The Transportation Research Board’s Research in Progress record for the NCHRP project “Development of the 8th Edition of AASHTO’s A Policy on the Geometric Design of Highways and Streets (Green Book)” shows a project started on 10 May 2021 and completed on 31 March 2026, with the goal of producing a draft for AASHTO balloting. A completed research project is not the same as a published edition: adoption is a separate AASHTO balloting step, and 23 CFR 625.4 still names the 7th edition as of the 2026-11-01 version.
Where it matters for labs and materials work
Pavement, aggregate and concrete laboratories do not apply the Green Book directly. It sets geometric design policy (what the road should provide), while laboratories report results against test methods and material specifications such as those discussed in our guides to ASTM C138 fresh concrete density, yield and air content, ASTM C76 reinforced concrete pipe and recycled asphalt pavement. Editorial interpretation: knowing which document is design policy and which is a test or material standard avoids citing the wrong one in a report or a project specification.
Common misunderstandings
- “The Green Book is a mandatory federal rule.” It is an AASHTO publication. It carries federal weight on NHS projects only because 23 CFR 625.4 incorporates a specific edition by reference; off the NHS, states keep discretion under the FHWA memo.
- “The newest edition is automatically the legal one.” The 2018 edition was guidance until rulemaking, and a newly balloted edition would need the same incorporation step.
- “It is a materials or testing standard.” It addresses geometric design, not specimen preparation or test procedures.
- “Its values are rigid.” AASHTO presents the 7th edition as flexible and performance-based, using context classes alongside functional classes.
FAQ
What does the AASHTO Green Book cover?
Geometric design of highways and streets, organised in the 7th edition around functional classes (local, collector, arterial, freeway) and context classes (rural, rural town, suburban, urban, urban core).
Which edition is current?
The 7th edition, published in September 2018, is the current published edition and the one named in 23 CFR 625.4(d)(1)(i).
Is an 8th edition published?
An NCHRP project to develop a draft 8th edition was completed on 31 March 2026. Publication follows AASHTO balloting, which is a separate step.
Is compliance with the Green Book required?
For NHS projects, the edition incorporated in 23 CFR 625.4 is the reference. Off the NHS, FHWA’s 2019 memo left states with their own discretion.
Sources
- AASHTO Journal, “AASHTO Releases 7th Edition of its Highway and Street Design Green Book”, 28 September 2018 (aashtojournal.transportation.org), read 2026-11-08.
- FHWA, memorandum HICP-10, 10 May 2019 (fhwa.dot.gov/design/standards/190510.pdf), read 2026-11-08.
- eCFR, 23 CFR 625.4(d)(1)(i), version dated 2026-11-01, read 2026-11-08.
- Transportation Research Board, Research in Progress record 1707200 (rip.trb.org/View/1707200), read 2026-11-08.
