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What the Green Book Does Not Contain

The Green Book is not a design manual. It provides guidance on the geometric dimensions of the roadway. This includes widths of travel lanes, medians, shoulders, and clear zones; the width and shape of medians; turning radii; and other dimensions. There are many aspects of design that are not directly addressed in the Green Book. What the Green Book Does Not Contain

The Green Book is not a design manual. It provides guidance on the geometric dimensions of the roadway. This includes widths of travel lanes, medians, shoulders, and clear zones; the width and shape of medians; turning radii; and other dimensions. There are many aspects of design that are not directly addressed in the Green Book. A number of these items are as follows:

  • Problem definition
  • Project definition
  • Definition of the termini of the project
  • Development of a project concept
  • Aesthetic treatment of surfaces
  • Design within the appropriate context
  • Selection of the appropriate guardrail/bridge rail
  • Determination of functional classification
  • Determination of the appropriate functional requirements, capacity, and level of service
  • Structure design
  • Landscape development
  • Selection of light fixtures
  • Roadside development
  • Traffic operations


Some of these items are addressed by reference in the Green Book, including:

  • The Roadside Design Guide, AASHTO, 1996.
  • The Manual on Uniform Traffic Control Devices for Highways and Streets (MUTCD), FHWA, 1988.
  • A Guide for Transportation Landscape and Environmental Design, AASHTO, June 1991.
  • Guide for the Development of Bicycle Facilities, AASHTO, August 1991.


Many fundamental questions that affect roadway design must be answered before the design phase begins and the application of the Green Book and/or State standards comes into play. Decisions are made during planning and project development, and it is then that road design starts. Decisions that are made before the design phase include:

  • Whether the proposed improvement will be two, four, six, or eight lanes
  • Whether the facility will have a median
  • Whether roadway junctions will be atgrade intersections or grade separated interchanges.


Design involves the difficult process of merging these previously determined design decisions with the appropriate design criteria used in the Green Book, working within the existing environmental and other important constraints, and using a designer's best judgment and experience to make decisions.


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