TM 5-822-2/AFM 88-7, Chap. 5
(3) Traffic.
streets and 15 percent of ADT for roads) adjusted for
(a) Traffic studies.
trucks, buses, and tracked vehicles in accordance with
The geometric
3-3b.(3) (b) above corresponding to a given road or
design criteria presented in tables 1-1 and 1-2 have been
street classification can be summarized as follows:
developed on the basis of horizontal area requirements
for various combinations of number and kind of vehicles
Effective DHV (Equivalent Passenger
expected in the traffic stream. The general unit for
Cars per Hour)
measurement of traffic is ADT; the basic fundamental
unit of measurement of traffic is DHV. Reasonable
values for ADT and DHV can be determined through
Class
Road
Street
≥900
≥1,200
proper traffic studies and analyses of traffic data. Traffic
A
studies will be made in accordance with methods
B
720-899
1,000-1,199
presented in Military Traffic Management Command
C
450-719
750-999
Pamphlet No. 55-8.
D
150-449
250-749
(b) Composition. Traffic on installation
E
10-149
25-249
roads and streets may consist of a combination of
F
<10
<25
passenger cars, light-delivery trucks, single-unit trucks,
truck combinations, buses, and half- or full-track tactical
DHV for various combinations of vehicular traffic is
vehicles. Trucks, buses, and tracked vehicles have
shown in tables 1-1 and 1-2. The larger the proportions
more severe operating characteristics, occupy more
of buses, trucks, and tracked vehicles present in the
roadway space, and consequently impose a greater
traffic stream during the selected design hour, the
traffic load on highways than do passenger cars and
greater the traffic load and highway capacity required.
light-delivery trucks. The average overall effect of these
The DHV of tables 1-1 and 1-2 diminishes for each
vehicles on traffic operation has been considered in
highway class as the percentage of buses. trucks, and
formulating tables 1-1 and 1-2 as follows:
tracked vehicles in the traffic stream increases. The
Number of Passenger Cars Replaced by One Truck,
tables provide design data for traffic containing 0, 10, 20,
Bus, or Tracked Vehicle (All Classes)
and 30 percent buses, trucks, and tracked vehicles.
Flat
Rolling
Mountainous
Design data for other percentages of these vehicles may
Terrain
Terrain
Terrain
be determined by interpolation. The type and mission of
2.0
4.0
8.0
the military installation will indicate the size and character
of vehicles that will be used in installation operations.
(c) Volume.
Traffic volumes are
For example, traffic within storage depots will contain a
expressed as DHV in tables 1-1 and 1-2. The ADT
larger percentage of trucks than traffic within a housing
represents the total traffic volume for the year divided by
installation.
365. It is a value needed to determine total service and
(4) Capacity.
economic justification for highways, but is inadequate for
(a) Conditions affecting capacity. The
geometric design because it does not indicate the
capacity of a road or street will vary with lane width,
significant variation in the traffic during seasons, days, or
distance to lateral obstructions. condition and width of
hours. If a road or street is to be designed so that traffic
shoulders, profile and alignment, and with the
will be properly served, considerations must be given to
composition and speed of traffic. These factors are
the rush-hour periods. The DHV is to be used as a basis
referred to collectively as prevailing conditions. Those
for geometric design. Limited studies made of traffic
factors depending on physical features of the highway
flows at military installations indicate that because of the
are called prevailing roadway conditions, and those
high frequency with which peak hourly traffic occurs, the
depending on the character of the using traffic are called
average daily peak (peak 15 minute period of traffic flow
prevailing traffic conditions. The term capacity in itself
times 4) can be economically and efficiently used as the
has no significance unless the prevailing roadway and
DHV. However, care must be taken in selection of the
traffic conditions are stated.
DHV. The DHV is the basis for selecting parameters
(b) Capacity
analysis
(Highway
which will determine the operating level of service for the
Capacity Manual). A principal objective of capacity
completed facility. The DHV in tables 1-1 and 1-2 is
analysis is the estimation of the maximum amount of
shown as 15 and 12 percent, respectively, of the ADT.
traffic that can be accommodated by a given facility.
These are median values selected for military
Capacity analysis would. however, be of limited utility if
installations. If data collected show other conditions to
this were its only
exist, then the actual TM 5-822-2/AFM 88-7, Chap. 5 or
predicted DHV should be used to determine the road or
street class. The effective DHV (12 percent of ADT for
3-3
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