Page 56 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

Table 19. Equivalent Traffic Calculation for New and Rehabilitation Design

y
[(1 + i) − 1]
Cumulative Equivalent Traffic: ET = 365 x AADE (1 + i) (15)
O
i
where ET = Cumulative equivalent traffic
i = Yearly AADE growth rate as a decimal fraction
AADE = AADE at the beginning of the calculation period
y = Time in years for the calculation period since the opening of the facility, the
structural design period for the design traffic determination
Inputs
AADE Years (y)
Design
New Design (future) AADE O at time of opening facility. Years since the opening of the facility,
traffic the structural design period.
I
AADE O at the date of the past opening
of the existing road. Calculated using Age of the existing road in years from
Past traffic Equation 13 and the number of years the past opening (D I ) to the date of
from the survey date to the opening the investigation (D INV ).
Rehabilitation date, D I (a negative number).
Design AADE O at time of opening the
Design rehabilitated road. Calculated using Structural design period (sdp) in years
(future) Equation 13 from AADE at the survey after the opening of the rehabilitated
traffic road.
time and the time to opening.

Rehabilitation design requires that the past cumulative equivalent traffic and future anticipated traffic are estimated.
Figure 24 illustrates the time-based relationship between the events used in the traffic calculation process for
rehabilitation design. The formula for calculating the past traffic is also used for projecting the future traffic from the
date of the traffic survey, Equation (15) with different input values. The input variables for Equation (15) for both
future and past equivalent traffic are given in Table 19.

Figure 24. Chronological Events for Rehabilitation Design Traffic Calculations

Section 4: Design Traffic Estimation
Page 45