TM 5-822-2/AFM 88-7, Chap. 5
Figure 3-2. Design policy for guardrails, guideposts, and earth slopes.
other than safety. Guardrails are normally required at
in tables 1-1 and 1-2 will be widened 2 feet to provide
locations where vehicles accidentally leaving the
space for installation of guardrails or guideposts.
roadway might be damaged, resulting in injury to
Guardrail ends should be flared outward, covered with a
occupants. Guardrails or guideposts should conform to
mound of earth, protected with a crash cushion or
local highway department criteria.
breakaway terminal cable, or buried on the traffic
(b) Design policy.
Guardrails or
approach end. Guardrails and alignment of guideposts
should be tapered in at narrow structures to meet curb
guideposts are not normally required where the front side
lines. See the AASHTO Guide for Selecting, Locating
slopes are 4:1 or flatter. Design policy for determining
and Designing Traffic Barriers for more information.
where guardrails or guideposts are required is shown in
(d) Marking. Guardrails and guideposts
figure 3-2. The ordinate of this figure, designated
must be highly visible, particularly at night. All guardrails
"Height of Cut or Fill in Feet," is used in this manual to
and guideposts shall be marked or painted in
refer to the vertical distance between the outside
accordance with AASHTO safety requirements.
(intersection of shoulder and front slope planes) edge of
(7) Earth slopes. In determining degree of
the shoulder and the toe of the front slope on fills, or
between the toe and top of back slope in cuts.
sides slopes for cut and fill sections, consideration must
(c) Location with respect of edge of
be given to stability, drainage,
pavement. Guardrails or guideposts should be located
at a constant offset from the edge of a pavement outside
the limits of the usable shoulder. Shoulder widths shown
3-12
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