Figure 3-5. Example selection of sample units to be surveyed.

(1) The "sampling interval" (i) is determined

was not selected at random and/or contains distress(es)

by i=N/n, where N=total number of available sample

which are not representative of the section.

(2) The calculation of the PCI when additional

units, n=minimum

number of sample units to be

sample units are included is slightly altered and its

surveyed, and i is rounded off to the smaller whole

described in paragraph 3-5.

number (e.g., 3.6 is rounded to 3).

(2) The random start (s) is selected at random

between 1 and the sampling interval (i). For example, if

a. General. Paragraph 3-4 described two ways of

i=3, the random start would be a number from 1 to 3.

inspecting a pavement section; i.e., inspecting every unit

(3) The sample units to be surveyed are

in the section or inspecting by sampling. Data collected

identified as s, s+i, s+2i, s+3i, etc. If the selected start is

during either method of inspection are used to calculate

3, then the samples to be surveyed are 3, 6, 9, 12, etc.

the PCI. This paragraph explains how to calculate the

(See fig 3-5.) This technique is simple to apply and also

PCI for a particular sample unit, and how to calculate the

gives the information necessary to establish a PCI profile

PCI for the entire pavement section. An important item

along the pavement section.

in the calculation of the PCI is the "deduct value." A

d. Selection of additional sample units. One of the

deduct value is a number from 0 to 100, with 0 indicating

major objections to sampling is the problem of not

the distress has no impact on pavement condition, and

including very "poor" or "excellent" sample units which

100 indicating an extremely serious distress which

may exist in a section. Another problem is the selection

causes the pavement to fail.

of a random sample which contains nontypical distresses

b. Calculating sample unit PCI. Calculating the PCI

such a railroad crossings, potholes, etc.

for a sample unit is a simple procedure which involves

(1) To overcome these problems, the

five steps (see fig 3-6):

inspector should label unusual sample units as additional

sample units. An additional unit implies that the sample