Bridges: Flexibility in the AASHTO Guidelines
The replacement or retention of bridges having historic or aesthetic value or the design of bridges on very low-volume roads may justify traveled way widths less than the indicated minimum AASHTO Green Book (2) values. The width evaluation should be... more
American Association of State Highway and Transportation Officals (AASHTO),
from A Guide for Achieving Flexibility in Highway Design,2004
Context Assessment
In order for a designer to be sensitive to the projects surrounding environment, he or she must consider its context and physical location carefully during this stage of project planning. Some of these issues to be considered are; the physical... more
Federal Highway Administration (FHWA),
from Flexibility in Highway Design
Cross-Section Elements: Bicycles
"Bicycles are...a viable mode of transportation..., both for commuting and recreation." Bicycles can use a shared lane, a wide outside lane, a regular designated bicycle lane, a shoulder or a multi-use path according to the specific context and... more
Federal Highway Administration (FHWA),
from Flexibility in Highway Design
Cross-Section Elements: Curbs
There are two types of curbs: barrier and mountable. Both in urban and suburban environments curbs serve functions such as drainage control, roadway edge delineation, and right-of-way reduction.
Federal Highway Administration (FHWA),
from Flexibility in Highway Design
Cross-Section Elements: Landscape Design and Plants
Landscape design is an important element to help mitigate nuisances and help the roadway fit the surroundings. Goal of landscape design is to provide vegetation to improve aesthetics and safety, lower constructions costs and create enough visual... more
Federal Highway Administration (FHWA),
from Flexibility in Highway Design
Cross-Section Elements: Medians
"Depending on agency practice and specific location requirements, medians may be
depressed, raised, or flush with the surface of the traveled way. Medians should have
a dimension that is in balance with the other elements of the total highway cross... more
Federal Highway Administration (FHWA),
from Flexibility in Highway Design
Cross-Section Elements: Transit
"Highways operate as truly multimodal transportation facilities, particularly in large urban areas. Accommodating public transit and other high-occupancy vehicles (HOVs) is an important consideration. On one end of the scale, this may involve... more
Federal Highway Administration (FHWA),
from Flexibility in Highway Design
Cross-Section Elements: Trees
"An important aspect of roadside landscape design is the treatment of trees ... Integrating trees into the design of a facility has many advantages. Trees provide a visual edge to the roadway that helps guide motorists. Trees also add to the... more
Federal Highway Administration (FHWA),
from Flexibility in Highway Design
American Association of State Highway and Transportation Officals (AASHTO),
from A Guide for Achieving Flexibility in Highway Design,2004
Decision Sight Distance (DSD): Mitigating Insufficient Decision Sight Distance
Designers should strive to provide three-dimensional alignments that produce DSD as part of
location planning and studies for new alignments, and in considering proposals to add new
intersections and interchanges to existing highways.
American Association of State Highway and Transportation Officals (AASHTO),
from A Guide for Achieving Flexibility in Highway Design,2004
Detailing the Design
Particularly during the final design phase, it is the details associated with the project that are important. Employing a multidisciplinary design team ensures that important design details are considered and that they are compatible with community... more
Federal Highway Administration (FHWA),
from Flexibility in Highway Design
Intersection Sight Distance (ISD): Mitigating Limited Intersection Sight Distance
Where limited ISD exists according to the AASHTO Green Book (2), the designer has a number of options depending on the nature of the sight restriction. Every attempt should be made to eliminate sight restrictions such as trees, vegetation, signs, and... more
American Association of State Highway and Transportation Officals (AASHTO),
from A Guide for Achieving Flexibility in Highway Design,2004
Medians: Flexibility in the AASHTO Guidelines
The AASHTO Green Book (2) offers considerable flexibility in the use and design of medians.
The Green Book (2) describes operational and safety advantages, provides appropriate widths for
different functions, and discusses tradeoffs. The use of... more
American Association of State Highway and Transportation Officals (AASHTO),
from A Guide for Achieving Flexibility in Highway Design,2004
Medians: Mitigating the Effects of Narrow Medians
Where medians do not exist or cannot be provided, designers should strive to mitigate potential adverse effects. Left-turn restrictions and the institution of access control can reduce rear-end/left-turn conflicts.
American Association of State Highway and Transportation Officals (AASHTO),
from A Guide for Achieving Flexibility in Highway Design,2004
Right-of-Way, Construction and Maintenance
Maintenance post-construction, involvement of design team in the implementation phase.Once the final designs have been prepared and needed right-of-way is purchased, construction bid packages are made available, a contractor is selected, and... more
Federal Highway Administration (FHWA),
from Flexibility in Highway Design
Road Width
The design element with the greatest effect on the scale of the roadway is its width, or cross section. Elements (or a lack of elements) along the roadside also contribute to the perceived width of the road and can even affect the speed at which... more
Federal Highway Administration (FHWA),
from Flexibility in Highway Design
Sidewalks and Pedestrian Paths
"[Sidewalks accomodate] pedestrians along the traveled way ... [and they are] equally important as the provision for vehicles ... The sidewalk can either be placed flush with the roadside edge ... or next to a buffer area, such as a planted strip,... more
Federal Highway Administration (FHWA),
from Flexibility in Highway Design
Jobs, mobility, economic prosperity - these are the kind of benefits that we
usually attribute to transportation. But theres a lot more to say about the
good transportation does, not just for today, but far into the future. Good
things... more
American Association of State Highway and Transportation Officals (AASHTO),
from AASHTO Center for Environmental Excellence,2003
Vertical Alignment (Grades): Flexibility in AASHTO Guidelines
(..)[T]he information on grades reflects design practices related to cost and
operational efficiency. The AASHTO Green Book (2) refers to "reasonable guide values for maximum designs," and further indicates that such guidelines are based primarily... more
American Association of State Highway and Transportation Officals (AASHTO),
from A Guide for Achieving Flexibility in Highway Design,2004
Vertical Alignment (Grades): Mitigating Steep Grades
Where it is necessary to accept a steeper than normal grade, designers should evaluate the
operational effects of the grade on heavy vehicles. The AASHTO Green Book (2) includes a set of design curves that enable estimation of vehicle speeds on... more
American Association of State Highway and Transportation Officals (AASHTO),
from A Guide for Achieving Flexibility in Highway Design,2004
