Cross-section elements define the highway right-of-way. This section describes each element and related factors effecting the design of the roadway.
CROSS-SECTION ELEMENTS
BACKGROUND
The cross section of a road includes some or all of the following elements:
Traveled way (the portion of the roadway provided for the movement of
vehicles, exclusive of shoulders)
Roadway (the portion of a highway, including shoulders, provided for
vehicular use)
Median area (the physical or painted separation provided on divided
highways between two adjacent roadways)
Bicycle and pedestrian facilities
Utility and landscape areas
Drainage channels and side slopes
Clear zone width (i.e., the distance from the
edge of the traveled way to either a fixed
obstacle or nontraversable slope)
Considered as a single unit, all these cross-section elements define the highway
right-of-way. The right-of-way can be described generally as the publicly owned
parcel of land that encompasses all the various cross-section elements (see Figures
6.1 and 6.2).
Some decisions about cross section are made during project development, such as
the capacity and number of lanes for the facility. Other decisions, such as functional
classification, are made earlier in the process. Within these parameters, the Green
Book guidelines recommend a range of values for the dimensions to use for
cross-sectional elements. Deciding which of the elements to include and selecting the
appropriate dimensions within these ranges is the role of the designer.
In selecting the appropriate cross-section elements and dimensions, designers need
to consider a number of factors, including the following:
Volume and composition (percent trucks, buses, and recreational
vehicles) of the vehicular traffic expected to use the facility
The likelihood that bicyclists and pedestrians will use the route
Climatic conditions (e.g., the need to provide storage space for plowed
snow)
The presence of natural or human-made obstructions adjacent to the
roadway (e.g., rock cliffs, large trees, wetlands, buildings, power
lines)
Type and intensity of development along the section of the highway
facility that is being designed
Safety of the users
The most appropriate design for a highway improvement is the one that balances the
mobility needs of the people using the facility (motorists, pedestrians, or bicyclists)
with the physical constraints of the corridor within which the facility is located.
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