AASHTO Green Book (GDHS-7) — A Policy on Geometric Design of Highways and Streets, 7th Edition — Includes October 2019 Errata
AASHTO Green Book GDHS-7, 7th Edition with October 2019 Errata covering geometric design of roads, streets, intersections, freeways and interchanges.
About this publication
Product Description
AASHTO GDHS-7, A Policy on Geometric Design of Highways and Streets, 7th Edition, commonly known as the AASHTO Green Book, is the American Association of State Highway and Transportation Officials' principal policy reference for the geometric design of highways and streets.
The seventh edition provides guidance for transportation engineers and designers developing new highways and streets, reconstruction projects and improvements to existing roadways. It incorporates current design research and established practice while introducing a framework that is more flexible, multimodal and performance-based than earlier editions.
This listing includes the October 2019 Errata. AASHTO's current downloadable edition incorporates those corrections directly into the publication.
Current Edition Status
The 2018 seventh edition remains the current published edition of the AASHTO Green Book as of October 2026. It supersedes the sixth edition published in 2011.
AASHTO has undertaken research and development work toward a future eighth edition, but an eighth edition has not yet replaced GDHS-7. The AASHTO Store continues to identify and sell the seventh edition as the current Green Book.
A New Framework for Geometric Design
One of the most important changes introduced in the seventh edition is a broader geometric-design framework intended to move beyond rigid application of nominal roadway criteria.
The Green Book emphasizes project-specific engineering judgment, context, transportation performance and the needs of multiple travel modes. The approach encourages designers to select geometric characteristics that respond to the project's purpose and need rather than treating every design value as an isolated target.
Functional Classification
The Green Book retains the traditional roadway functional-classification system. The principal functional classes addressed include:
local roads and streets;
collectors;
arterials;
freeways.
Functional classification considers the role a roadway serves within the transportation network, including the balance between mobility and access.
Context Classification
The seventh edition supplements functional classification with five specific context classifications:
Rural
Rural Town
Suburban
Urban
Urban Core
The combination of functional class and context provides a more complete basis for selecting appropriate roadway design characteristics. An arterial in a rural environment can have substantially different design objectives and physical characteristics from an arterial passing through an urban core, even though both serve an arterial transportation function.
Flexible and Performance-Based Design
The seventh edition expands the Green Book's use of flexible design and introduces a stronger performance-based approach. Designers are encouraged to consider safety, operations, mobility, accessibility, multimodal use, surrounding land use, environmental conditions, available right-of-way and project constraints when selecting geometric design features.
This approach is particularly relevant to reconstruction and existing-road projects where applying new-construction criteria without regard to context can create unnecessary cost, environmental impacts, property impacts or conflicts with pedestrian, bicycle and transit needs.
Multimodal Transportation
The 7th Edition gives greater attention to transportation of people rather than focusing almost exclusively on motor vehicles. Pedestrians, bicyclists, transit users and motorists are considered within the geometric-design process.
Chapter 2 was reorganized specifically to strengthen this multimodal emphasis and to provide greater consideration of lower-speed, walkable urban environments.
Chapter 1 — New Framework for Geometric Design
Chapter 1 was completely rewritten for the seventh edition. It introduces the updated framework for flexible, performance-based geometric design and explains how functional and context classifications can be used together.
The chapter addresses project purpose and need, roadway functional classification, context classification and application of the design framework to new construction, reconstruction and projects on existing roadways.
This chapter represents a major philosophical change from previous Green Book editions by emphasizing that good geometric design involves balancing project-specific objectives rather than simply selecting dimensions from tables.
Chapter 2 — Design Controls and Criteria
Chapter 2 addresses the characteristics of road users, vehicles and traffic that influence geometric design. The seventh edition reorganizes this material to focus more broadly on movement of people and multimodal transportation.
Subjects include factors such as:
drivers and human factors;
pedestrians;
bicyclists;
design vehicles;
traffic characteristics;
design speed;
operating conditions;
multimodal level of service;
lower-speed urban and walkable environments.
Pedestrian walking-speed information was updated based on more recent research, supporting improved evaluation of pedestrian crossings and intersection design.
Design Vehicles
Vehicle dimensions and operating characteristics influence lane widths, intersection geometry, turning-roadway design and other geometric elements. The Green Book contains design-vehicle information for passenger vehicles, buses, single-unit trucks and various combination vehicles.
Designers use an appropriate design vehicle based on expected roadway use rather than simply designing every facility around the largest possible vehicle.
Design Speed
Design speed remains an important control in establishing geometric design characteristics, including horizontal curvature, vertical alignment and sight distance.
The seventh edition also emphasizes the relationship among design speed, expected operating behavior, roadway context and project objectives, particularly in lower-speed urban environments.
Chapter 3 — Elements of Design
Chapter 3 addresses fundamental geometric-design elements that apply across roadway functional classifications. These include sight distance, horizontal alignment, superelevation and vertical alignment.
The seventh edition incorporates updated research and expanded design-speed ranges while providing additional flexibility in geometric design calculations.
Stopping Sight Distance
Stopping sight distance represents the distance needed for a driver to perceive a condition, react and stop the vehicle. It is one of the principal controls for highway and street geometric design.
The seventh edition adds an 85 mph design speed to stopping-sight-distance tables, extending the design information available for very high-speed facilities.
Passing Sight Distance
The Green Book addresses passing sight distance for appropriate two-lane roadway applications where drivers may use an opposing traffic lane to overtake slower vehicles.
Passing opportunities interact with horizontal alignment, vertical alignment, traffic conditions and pavement-marking requirements.
Decision Sight Distance
Decision sight distance provides additional visibility where drivers may need more time to detect, recognize and respond to complex or unexpected roadway conditions. Such locations can include interchanges, lane transitions and areas with unusual geometrics or visual complexity.
Horizontal Alignment
Horizontal-alignment guidance covers tangent roadway sections and horizontal curves. Design of horizontal curves considers design speed, radius, superelevation and side-friction demand.
The seventh edition explains how to compute superelevation and minimum radius for design speeds greater than 80 mph.
Superelevation
Superelevation is the transverse roadway slope used on horizontal curves to assist vehicles in negotiating curvature. The seventh edition provides greater flexibility in the distribution and rate of superelevation rotation through transition areas.
It also introduces an equation for checking potential oversupply of superelevation during transitions.
Vertical Alignment
The Green Book provides geometric-design guidance for roadway grades and vertical curves. Crest and sag vertical curves are designed in coordination with sight distance, operating characteristics, drainage and driver comfort.
Vertical alignment must also be coordinated with intersections, structures, drainage systems and the surrounding terrain.
Chapter 4 — Cross-Section Elements
Chapter 4 addresses the physical elements that form the roadway cross section. These elements determine how space is allocated among roadway users and influence safety, operations, drainage, accessibility and roadside conditions.
Topics include:
traveled ways and lane widths;
shoulders;
medians;
roadsides and border areas;
curbs;
sidewalks and pedestrian facilities;
bicycle accommodations;
driveways;
drainage considerations;
cross slopes;
roadside features.
Lane Width and Traveled Way
Lane-width selection depends on roadway function, context, speed, traffic composition and constraints. The Green Book provides design guidance rather than assuming a single lane width is appropriate for every roadway.
This flexibility is especially significant in constrained urban and multimodal environments where wider motor-vehicle lanes can conflict with pedestrian, bicycle, transit or right-of-way objectives.
Shoulders
Shoulders can provide emergency stopping space, structural pavement support, recovery area and accommodation for bicyclists and other functions. Appropriate width and treatment depend on roadway type, traffic volume, speed and context.
Medians
Medians can separate opposing traffic, provide space for turning movements, accommodate barriers, support access management and provide pedestrian refuge depending on their configuration and width.
Pedestrian and Bicycle Accommodation
The seventh edition's multimodal framework encourages explicit consideration of pedestrian and bicycle needs when developing roadway cross sections. Appropriate facilities depend on context, speed, traffic volumes, adjacent development and expected users.
Chapter 5 — Local Roads and Streets
Chapter 5 provides geometric-design guidance for local roads and streets. Local facilities emphasize access to adjacent property and generally carry lower traffic volumes than collectors and arterials.
The chapter distinguishes rural local roads from local streets in suburban, urban and urban-core environments and encourages designs appropriate to neighborhood and land-use context.
Local Streets in Urban Areas
Urban local streets are intended to be designed using a flexible approach that reflects surrounding development and the needs of all relevant transportation modes. Lower operating speeds are generally appropriate because access and neighborhood functions receive greater emphasis than through mobility.
Chapter 6 — Collector Roads and Streets
Chapter 6 addresses collector facilities, which link local road and street systems with arterial networks. Collectors serve both access and mobility functions and can operate in rural, suburban and urban environments.
Design considerations include alignment, cross sections, intersections, pedestrian and bicycle accommodations and the relationship between adjacent development and through traffic.
Chapter 7 — Arterial Roads and Streets
Chapter 7 addresses arterial facilities, which place greater emphasis on mobility and movement of larger traffic volumes while still interacting with surrounding land uses and access needs.
For consistency with Chapters 5 and 6, the seventh edition changed the chapter title to Arterial Roads and Streets.
The chapter includes geometric considerations for arterial facilities in different contexts and added specific discussion of the rural town context. It also adds material on speed management in urban areas.
Access and Driveways
Arterial geometric design often requires balancing through movement with access to adjacent properties. Driveway frequency, spacing, median design, turning movements and intersection configuration can substantially influence both safety and traffic operations.
Public Transit Facilities
The arterial chapter includes consideration of public transit facilities, including bus-stop location and bus turnouts. Transit facilities must be coordinated with traffic operations, pedestrian access and roadway cross-section design.
Chapter 8 — Freeways
Chapter 8 provides geometric-design guidance for freeways, which are divided highways designed primarily for through movement with full control of access.
Freeway design topics include:
basic freeway cross sections;
alignment;
medians and shoulders;
clearances;
auxiliary lanes;
access control;
operational considerations;
coordination with interchanges and ramps.
The high-speed, access-controlled character of freeways requires close coordination of sight distance, alignment, roadside conditions and interchange geometry.
Chapter 9 — Intersections
Chapter 9 contains comprehensive geometric-design guidance for at-grade intersections. Intersection design must accommodate conflicting movements among vehicles, pedestrians, bicycles and transit while providing adequate sight distance and understandable paths through the intersection.
Topics include:
intersection alignment and profile;
sight distance;
turning roadways;
corner geometry;
channelization;
turn lanes;
median openings;
U-turns;
roundabouts and other intersection forms;
railroad-highway grade crossings.
Intersection Sight Distance
Intersection sight distance is evaluated using clear sight triangles that allow drivers to see potentially conflicting traffic and complete the required maneuver safely.
The appropriate sight-distance case depends on the traffic-control condition and maneuver being performed.
Turning Movements
Intersection geometry must accommodate the applicable design vehicle while avoiding unnecessary pavement area and excessive pedestrian crossing distances. The Green Book includes swept-path and turning-design information for common design vehicles.
Median Openings and U-Turns
The intersection chapter provides guidance for median openings and U-turn arrangements on divided highways and streets. These features must be coordinated with roadway width, traffic volume, design vehicle and access requirements.
Railroad-Highway Grade Crossings
Chapter 9 addresses geometric considerations for highway-rail grade crossings, including crossing geometry and sight distance needed for vehicles to approach, stop where required and cross railroad tracks.
Chapter 10 — Grade Separations and Interchanges
Chapter 10 provides guidance for grade separations and highway interchanges. These facilities allow intersecting traffic streams to cross at different elevations and can provide controlled connections through ramps.
The chapter covers the selection and geometric design of grade separations, interchange configurations, ramps, terminals and speed-change lanes.
Interchange Types
The Green Book discusses interchange forms appropriate to different traffic, site and roadway conditions. Configurations include variations of three-leg, diamond, cloverleaf and directional interchanges.
Selection involves consideration of traffic operations, available right-of-way, terrain, interchange spacing, construction cost and expected future development.
Grade Separation Structures
Grade-separation design considers roadway profile, vertical clearance, structure arrangement, lateral offset, sight distance and the relationship between the structure and the intersecting facilities.
Ramps
Ramp geometric design addresses design speed, horizontal and vertical alignment, cross section and connections with the freeway and crossroad.
The Green Book provides guide values relating ramp design speed to highway design speed and guidance concerning maximum ramp grades.
Entrance and Exit Terminals
Entrance and exit ramp terminals are designed to support safe transitions between freeway through lanes and ramps. Acceleration and deceleration lanes provide space for vehicles to adjust speed outside the primary freeway traffic stream.
The Green Book provides minimum acceleration- and deceleration-lane lengths and adjustment factors for roadway grade.
October 2019 Errata
AASHTO issued formal errata for the seventh edition in October 2019. The current AASHTO downloadable PDF incorporates these corrections, and AASHTO also provides the errata separately for users of earlier print copies.
This listing represents the seventh edition with the October 2019 corrections incorporated.
Relationship to Federal Highway Design Criteria
FHWA reviewed the 2018 Green Book following its publication and concluded that its updates met or improved upon the criteria in the previous 2011 edition. FHWA subsequently allowed state departments of transportation to adopt the 2018 Green Book for National Highway System projects under the applicable federal framework.
Designers should nevertheless verify the specific standards adopted by the highway agency or authority having jurisdiction for the project because state, local and federal requirements can establish additional or modified criteria.
Use With Other Transportation Design References
The Green Book does not attempt to contain every roadway-design requirement. Depending on the project, designers commonly coordinate it with other AASHTO, FHWA and jurisdictional references addressing subjects such as roadside safety, pedestrian facilities, bicycle facilities, traffic control devices, bridges, drainage and low-volume roads.
Who Should Use the AASHTO Green Book
highway and roadway design engineers;
transportation engineers;
civil engineers;
municipal street designers;
state departments of transportation;
county and municipal transportation agencies;
transportation planners;
traffic engineers;
multimodal and complete-streets designers;
consulting engineering firms;
roadway project managers;
public works departments;
plan reviewers and design reviewers;
transportation engineering educators and students;
Professional Engineer examination candidates where the applicable exam specification references this edition.
Why the Seventh Edition Matters
The seventh edition represents an important transition in AASHTO geometric-design policy. Earlier design practice often emphasized motor-vehicle mobility and selection of nominal geometric criteria. GDHS-7 explicitly adds context classification, multimodal considerations and a performance-based framework.
This allows engineers to evaluate geometric design as a coordinated response to roadway function, community context, transportation users and project performance rather than simply applying one geometric template to every road or street.
Product Features
7th Edition of AASHTO's A Policy on Geometric Design of Highways and Streets
Commonly known as the AASHTO Green Book
Current published edition as of October 2026
Includes October 2019 Errata
1,047-page downloadable edition
Introduces flexible and performance-based geometric design
Includes multimodal transportation considerations
Combines functional classification with five context classifications
Covers rural, rural-town, suburban, urban and urban-core contexts
Addresses project purpose and need
Covers design controls and design vehicles
Covers stopping, passing and decision sight distance
Addresses horizontal alignment and superelevation
Covers vertical alignment and vertical curves
Includes roadway cross-section design
Covers local roads and streets
Covers collector roads and streets
Covers arterial roads and streets
Covers freeway geometric design
Provides comprehensive intersection guidance
Covers grade separations and interchanges
Includes ramp and speed-change-lane design guidance
Product Details
Publication: A Policy on Geometric Design of Highways and Streets
Common Name: AASHTO Green Book
Publication Code: GDHS-7
Edition: 7th Edition
Publisher: American Association of State Highway and Transportation Officials (AASHTO)
Publication: September 2018
Print ISBN: 978-1-56051-676-7
PDF Page Count: 1,047
Errata: October 2019 Errata incorporated
Previous Edition: 6th Edition, 2011
Language: English
Publication Type: Highway and Street Geometric Design Policy
Edition Status Note
The seventh edition remains the current published edition of A Policy on Geometric Design of Highways and Streets as of October 2026. It supersedes the sixth edition published in 2011. The current AASHTO PDF incorporates the October 2019 Errata. Research and development activities for a future eighth edition have been undertaken, but no eighth edition has yet superseded GDHS-7.