of all its sample units. Inspection by sampling, however,

as follows:

requires a different approach. If all surveyed sample

Density =

number of slabs containing a particular type X 100

units are selected randomly, the PCI of the pavement

distress number of slabs in sample unit

section is determined by averaging the PCI of its sample

units. If any additional sample units are inspected, a

For example, two slabs in the pavement sample unit

weighted average must be used. The weighted average

shown in figure 3-2 contained linear cracking (distress

is computed by using the following equation:

28) at medium severity, so the density is calculated as 2

20X 100, or 10 percent. The deduct values are then

PCIs = (N-A)(PCI1 + A)(PCO1) + A(PCO2)

determined for each distress combination from the

N

(Equation 3-1)

distress deduct value curves given in figures C-21

through C-39. The CDV is determined from figure C-40,

where PCIs = PCI of pavement section, PCI1 = average

and the PCI is calculated as shown in figure 3-2.

PCI of random samples, PCI2 = average PCI of

e. Determination of distress quantities for a

additional samples, N = total number of samples in the

pavement section.

When a pavement has been

section, and A = number of additional samples

inspected by sampling, it is necessary to extrapolate the

inspected.

quantities and densities of distress over the entire

pavement section to determine total quantities for the

d. Example calculation of the PCI for a sample unit.

section.

The field data sheets described in paragraph 3-3 are

(1) If all sample units surveyed were selected

always used when calculating the PCI of a sample unit.

at random, the extrapolated quantity of a given distress

(1) Asphalt pavement inspection sheet (fig 3-

of a given severity level would be determined as

3).

illustrated in the following example for medium-severity

(a) The difference between calculating

alligator cracking:

a PCI for an asphalt sample unit and calculating a PCI

for a concrete sample unit is in the way the distress

Section Information

density is determined.

Surface type: Asphalt concrete

1. Density for distresses measured by

Area: 24,500 square feet

the square foot is calculated as follows:

Total number of sample units in the section: 10

Density =

distress amount in square feet

sample unit area in square feet

X100

Five sample units were surveyed at random, and the

amount of medium-severity alligator cracking was

2. Density for distresses measured by

determined as follows:

the linear foot (bumps, edge cracking, joint reflection

cracking, lane/shoulder drop off, and longitudinal and

Sample

Sample Unit

Medium-Severity Alligator

transverse cracking) is calculated as follows (see

Unit ID

appendix B for distress definitions):

Number

Area, Square Feet

Cracking, Square Feet

02

2500

100

Density =

distress amount in linear feet

04

2500

200

sample unit area in square feet

X100

06

2500

150

08

2500

50

3. Density for distress measured by number (potholes)

10

2000

100

is calculated as follows:

Total

Random

12,000

600

Density =

number of potholes

sample unit area in square feet

X100

The average density for medium-severity alligator

(b) After the distress density for each distress

cracking is, therefore, 600/12,000 = 05.

The

extrapolated quantity is determined by multiplying the

type/severity combination is calculated, the deduct

density by the section area, i.e., .05X24,500=1225

values are determined from the distress deduct value

square feet.

curves in figures C-1 through C-19 of appendix C. The

(2) If additional sample units were included in

corrected deduct value (CDV) is determined from figure

the survey, the extrapolation process would be slightly

C-20 and is calculated as shown in figure 3-3.

(2) Concrete pavement inspection sheet (fig

different. In the example given in (1) above, assume that

sample unit number 01 was surveyed as additional and

3-2). After inspection, calculate the density of distress

that the amount of medium-severity alligator cracking