TM 5-822-2/AFM 88-7, Chap. 5
Area Designation
Used in Highway
Capacity Manual
Equivalent Area at Military Installations
Downtown
Central portion of built-up areas at major installations
Fringe, business dis-
Central portion of built-up areas at all but major installations. Indus-
trict
trial, service, and warehouse areas at major installations
Outlying business dis-
Residential portion of built-up areas at major installations. Indus
trict and intermedi-
trial, service, warehouse, and residential portions of built-up areas
ate residential
at intermediate installations. All built-up areas at small installations, isolated shopping
centers, community centers, and similar areas of public assembly in open areas.
Isolated road intersections in open areas
Rural
See Page 137, TRB Highway Capacity Manual
(4) Capacity of intersections. Intersection of
intersections with high-volume combinations, the cross-
traffic interference causes a wavelike behavior of through
high traffic volumes is one prevailing traffic condition
traffic similar to traffic controlled by traffic signals. Thus,
which will reduce average running speed and therefore
the capacity of intersections where uninterrupted flow
reduce capacity. The capacity (DHV) shown in tables 1-
cannot be assumed should be computed as if the
1 and 1-2 is for free-flowing highways without
intersections were operated under signal control
intersections at grade or with few crossroads carrying
irrespective of whether signal control is used. The
minor traffic. These highways have no traffic control
AASHTO procedure is suggested as a guide in design of
signals at intersections (plain unsignalized intersections);
intersections. Certain traffic volume combinations will
capacity is affected very little, and uninterrupted flow is
require wider traffic lanes on one or both intersecting
assumed. With no traffic control, as cross- and turning-
highways to assure desirable operating conditions at
traffic volume increases, vehicles on both intersecting
signalized intersections.
An analysis of various
highways may have to slow down or come to a complete
intersection traffic volumes assuming average conditions
stop, reducing capacity. Relief from this situation may be
and signal control has been made to show what
obtained by designating one of the intersecting highways
maximum traffic volume combinations may be used
as the major one, and controlling traffic on the minor
without requiring additional lane width. If the following
highway by stop signs. The traffic on the major highway
volume combinations are exceeded, additional lane width
can then be assumed to be uninterrupted. However, if
in excess of that shown in tables 1-1 and 1-2 for
traffic volume on the minor highway increases to the
classified roads and streets will be required.
point that cross traffic cannot be properly controlled by
stop signs, traffic control signals generally follow. At
AASHTO Suggested Design Hourly Volume Combinations Which
Signal Control Should be Assumed in Geometric Design of
Intersections Minimum DHV Two-way on:
2-lane through highway
400
500
650
Crossroad
250
200
100
4-lane through highway
1,000
1,500
2,000
Crossroad
100
50
25
Note:
These volumes have no relation to warrant for signalization, nor do they indicate whether or not signalization
should be used after the intersection is open to traffic
This tabulation may serve as a general guide for design
analysis is required. If the DHV of traffic is greater than
of at-grade intersections in the following manner: If the
that shown in this tabulation, the intersection should be
DHV of traffic at a given intersection is approximately
designed as if it were under signal control.
The
equal to or less than that shown in the tabulation,
geometric layout should be made in conjunction with an
capacity of the through highway is based on the DHV
intersection capacity analysis, as in the TRB Highway
shown in tables 1-1 and 1-2, and no intersection capacity
Capacity Manual. The volumes shown in this tabulation
3-21
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