TM 5-826-6/AFR 93-5
Figure 4-1. Selection of minimum number of sample units.
d. All the sample numbers within a feature are numbered and those that are multiples of the interval i are selected for
inspection. The first sample unit to be inspected should be selected at random between 1 and i Sample unit size should
be 5,000 square feet (generally 50 by 100 feet) for flexible pavement and 20 adjacent slabs for rigid pavement. However,
as necessary the following sample unit size variation is acceptable: flexible 500 SF 1000 SF; rigid 20 5 slabs. Figures
4-2 and 4-3, respectively, illustrate the division of a jointed rigid pavement and flexible pavement feature into sample units.
Each sample unit is numbered so it can be relocated for future inspections, maintenance needs, or statistical sample
purposes. Each of the selected sample units must be inspected and its PCI determined. The mean PCI of a pavement
feature is determined by averaging the PCI of each sample unit inspected within the feature. When it is desirable to
inspect a sample unit that is in addition to those selected by the above procedure (because it is felt that very poor or
excellent units were omitted), then one or more additional sample units may be inspected, and the mean PCI of the feature
computed from
(eq 4-3) PCIf = (N - A) + A PCI2
N
N
where
PCIf = mean PCI of feature
N = total number of sample units in feature
A = number of additional sample units
PCI1 = mean of PCI for number of statistically selected units
PCI1 = mean of PCI for all additional sample units
4-2
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