TM 5-822-13/AFJMAN 32-1018
CHAPTER 3
VEHICULAR TRAFFIC
ments, but one operation of a tandem axle is one stress
3-1. Effect on Pavement Design.
repetition in a rigid pavement and is more than one
Pavement thickness is determined from anticipated
stress repetition in a flexible pavement. For instance,
traffic data which include types, distribution, and load-
for one operation of a tandem-axle dual-wheel load, it
ings of vehicles. Types include cars, light and heavy
is one stress repetition in a rigid pavement and two
trucks, tanks, and forklifts. Distribution covers the
stress repetitions in a flexible pavement. Relations
average daily volume of each type of vehicle which, in
between load repetition and required pavement thick-
turn, determines the total volume of traffic anticipated
ness developed from accelerated traffic tests of full-
during the design life of the pavement. Vehicle load-
scale pavements have shown that, for any given
ings include maximum single-and tandem-axle pneu-
vehicle, increasing the gross weight by as little as 10
matic-tire loads and gross weight of the heaviest
percent can be equivalent to increasing the volume of
tracked vehicle. For most pavements, the magnitude
traffic by as much as 300 to 400 percent. On this ba-
of the axle load is of greater importance than the gross
sis, the magnitude of the vehicle loading must be con-
weight of pneumatic-tired vehicles. Thus, for the case
sidered as a more significant factor in the design of
of pneumatic-tired vehicles having equal axle loads,
pavements than the number of load repetitions.
the increased severity of loading imposed by conven-
tional four-or five-axle trucks as compared with that
3.2 Vehicle Representative Configurations.
imposed by two- or three-axle trucks is largely a fa-
For determining pavement design requirements, ve-
tigue effect resulting from an increased number of load
hicles have been divided into three general groups.
repetitions per vehicle operation. For forklift trucks
They are pneumatic-tired vehicles (cars, trucks, buses,
where the loading is concentrated largely on a single
etc.) tracked vehicles, and forklift trucks (including
axle, the severity of the loading is a function of the
both solid and pneumatic tires). Each group has been
gross weight of the vehicle and the frequency of load-
divided into representative load configurations, and
ing. For tracked vehicles where the loading is evenly
table 3-1 shows data for these representative configu-
divided between the two tracks and nearly evenly di-
rations.
vided among the bogies, the severity of the track load-
3-3. Traffic Evaluation.
ing is a function of the gross weight of the vehicle,
number of bogies, and the frequency of loading. In
Procedures for the evaluation of future traffic and
pavement design, one operation of a single axle is one
determination of a design index are contained in
stress application for both flexible and rigid pave-
TM 5-822-2/AFM 88-7, Chap. 5.
3-1
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