Page 55 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

i = [(1 + h)(1 + v) − 1] (13)

where i = yearly AADE growth rate as a decimal fraction
h = yearly heavy vehicle volume growth rate as a decimal fraction
v = yearly E80/HV growth rate as a decimal fraction

4.5 Sequence of Events and Cumulative Design Traffic

The chronological sequence of events is important when determining the design traffic. The following three dates
are necessary:
• Date of the traffic investigation
• Date of design
• Date of opening

The process of projecting the AADE from the survey date to the date of design, followed by the accumulation of the
equivalent traffic for the duration of the structural analysis period is illustrated in Figure 23.

P
Projection with rojection with
cumulative umulative
c
D
Design Trafficesign Traffic c compound growthompound growth
Cumulative Cumulative equivalent traffic equivalent traffic

T
Timeime
Duration of structural analysis period, yation of structural analysis period, y
Dur
AADE AADE AADE P
Projection with rojection with
AADE OO
c
AADE compound growthompound growth
AADE SS
Da
Da
Date of end of structural te of end of structural
Date of traffic te of traffic Date of te of Da T
Timeime
survey, D opening, D analysis period, D
analysis period, D YY
survey, D SS
opening, D OO

Figure 23. Sequence of Events

The date of the traffic survey and design may coincide, but if historical traffic data is used for the design, these dates
differ. The AADE determined from the traffic survey data is projected to the AADE at the date of opening, using a
compound growth calculation given by Equation (14).

AADE = AADE (1 + i) (14)
n
O S

where AADE O = AADE at the time of opening the facility
AADE S = AADE at the time of the traffic investigation
i = yearly AADE growth rate as a decimal fraction
n = Time (years) from the date of the traffic investigation to the date of opening

Once the facility is opened to traffic, the cumulative equivalent traffic (ET) is calculated for the duration of the
structural design period using the cumulative compound growth equation (Equation (15) in Table 19). The
cumulative equivalent traffic at the end of the structural design period is the design traffic or traffic demand that
must be provided by the structural pavement design.

Section 4: Design Traffic Estimation
Page 44