TM 5-822-2/AFM 88-7, Chap. 5
(c) Location in regard to lane width
(5) Medians.
(a) Uses. Where traffic volume requires
includes type I, III, or IV (barrier) curbs. It is known that
vehicles tend to veer away from lateral obstructions
construction of multilane highways, opposing traffic
including barrier curbs. It has been found that lateral
should be separated by medians. Medians should be
placement of the vehicle varies with slope of face, height,
highly visible both day and night, and there should be a
and length of barrier curbs. This tendency reduces the
definite color contrast between median and traffic lane
capacity of traffic lanes adjacent to barrier curbs. It is
paving. The absolute minimum width for a median is 4
necessary therefore to offset barrier curbs a sufficient
feet with a desirable minimum width of 14 feet.
(b) Types. Cross sections of medians
distance from the edge of the nearest traffic lane to
prevent reduction in capacity. Curb offset and traffic lane
are illustrated in figure 3-1. It is not necessary that
width for classified roads and streets designed with
medians be of uniform width throughout the length of
barrier curbs are shown in tables 1-1 and 1-2.
divided highways.
Mountable curbs (type II) cause very little, if any, lateral
(c) Curbs. Special types of curbs for
displacement of traffic adjacent to these curbs; therefore,
medians are-not required. Where they are designed with
it is acceptable to locate type II curbs at the edge of a
curbs, one of the standard-type curbs shown in CE
traffic or parking lane.
Standard Drawing No. 40-17-02 will be used. Barrier
(4) Shoulders.
curbs adjacent to medians will be offset the same
(a) Width. Usually the outside edge of
distance shown for barrier curbs in tables 1-1 and 1-2.
the shoulder (intersection of shoulder and front slope
All design criteria relative to curbs presented herein are
plane) will be rounded. Rounding on shoulder edges
applicable to median curbs.
(d) Shoulders. Full-width shoulders are
improves the general appearance of the highway and
reduces maintenance costs but causes a reduction in
provided adjacent to the right (outside) lane of each
shoulder width. The steeper the front slope, the greater
pavement of divided highways to accommodate stopped
the reduction in width. Where front slopes are 4:1 or
vehicles. The shoulder adjacent to the left (inside) lane
steeper, the overall shoulder width from table 1-1 or 1-2
need not be wider than 4 feet. Shoulder strips are
will be increased in accordance with the tabulation below.
usually of contrasting color and are intended to increase
Increase Minimum Shoulder Widths
safety and decrease maintenance costs. Where the
Front Slope in
Shown in Tables 1-1 and 1-2 by
pavements of divided highways are at different levels
Cuts or on Fills
Amount Shown, feet
and separated by wide medians, the shoulder adjacent to
the left lane is more important than in other types of
4:1
0.0
divided highways from a safety viewpoint, and a shoulder
3:1
1.0
of normal width should be provided adjacent to this lane.
2:1
2.0
1
The minimum width for these median shoulders is 6 feet;
1 /2:1
3.0
8-feet shoulders should be provided where feasible.
On highways designed with mountable curbs, the width
(e) Design
for
specific
projects.
of curb and gutter sections is included in the minimum
Geometric design of medians for specific projects will be
shoulder widths shown for roads and streets designed
in accordance with AASHTO Highway Design and
without barrier curbs in tables 1-1 and 1-2. Where
Operational Practice Related to Highway Safety and the
guardrails or guideposts are required, the shoulders
should be widened an additional 2 feet (see 3-3c.(6)
Transportation Research Board Highway Capacity
Manual.
below).
(6) Guardrails and guideposts.
(b) Shoulders for roads. Roads in rural
(a) Uses. For safety and guidance of
areas are normally designed without curbs and require
traffic, guideposts should be provided at all locations
full width shoulders to accommodate high traffic
along roadways where drivers may become confused,
volumes. Geometric design criteria for shoulders on
particularly at night, as to the direction of the roadway;
roads are presented in table 1-1.
(c) Shoulders for streets. As a general
along roadways subject to periodic flooding; along
roadways where fog exists for long periods of time; and
rule, streets in cities are designed with some type of
where driving off the roadway is prohibited for reasons
barrier curb and do not require shoulders except where
needed for lateral support of the pavement and curb
structure.
Where lateral support is required, the
shoulder should be at least 4 feet in width where
feasible. In other sections within built-up areas, where
desirable to design streets without barrier curbs,
geometric design criteria are presented in table 1-2.
3-10
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