Page 63 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

Table 22. Worked Example: Design Traffic Calculation using Published Data (CTO)

Parameter Data Comments
Step 1: Determine General Design Input Parameters
Time of traffic survey or
date of published/known 2010/12/31 From CTO data (Figure 26).
data
Date of opening 01/01/2013 Assumed from project data.
Step 2: Determine the Four Basic Input Parameters
Daily heavy vehicle volume ADTT from CTO Data in
per lane for the base year 682 Figure 26.
(HVV)
Assumed from Table 17,
range of 4 – 7% (routes
Heavy vehicle volume 5% connecting centres of
growth rate (h) moderate economic
development, long-term
values).
Estimated average E80/truck
E80/HV at the survey time 1.5
from CTO Data in Figure 26.
Assumed from Table 18, for
E80/HV growth rate (v) 2%
“all heavy”.
Combined heavy vehicle i = [(1+h)(1+v)-1]
growth and E80/HV growth = [(1+0.05)(1+0.02)-1] Equation (13), input from this
= 0.07 step.
Step 3: Calculate the ADE at the Time of the Traffic Survey
CTO Data in Figure 26
Adjust for lane distribution N/A
indicates only 1 lane.
E80 Equation (4), input from Step
ADE = HV ∙ HVV 1.5 ∙ 682 2.
duration x lanes = 1 ∙ 1 Data duration for full year.
= 1023

Step 4: Adjust ADE to AADE
Weekend/weekday
variation
Seasonal variation N/A Data available for full year.
Exceptional periods
ADE = AADE = 1023 No adjustments for variations.
Step 5: Project AADE from Date of Traffic Survey to Date of Opening
Time from survey to 2 years
opening date (n)
n
AADE at time of opening AADE O = AADE S ⋅(1+i)
= 1023⋅(1+0.07) 2 Equation (14), input from
= 1171 Steps 3 and 2.
Step 6: Calculate Equivalent Design Traffic
Structural design period 20 years Design assumption.
Equivalent traffic
y
[(1 + i) − 1]
ET = 365 ∙ AADE (1 + i) Equation (15), input from
O
i Steps 6 and 2.
= 365 ∙ 1171 (1 + 0.07) [(1 + 0.07) 20 − 1]
0.07
= 18 748 635
= 18 million E80s (18 MESA)

4.7.2 Sensitivity Analysis

The design traffic estimation relies on a number of input variables determined from traffic surveys or estimated.
These inputs are therefore not exact and can vary. The sensitivity of the design traffic estimate to variation in the
inputs must be evaluated. This is done with a simple sensitivity analysis. To do this, assign a low, medium and high
value to each input variable, and repeat the design traffic calculation at different combinations of the inputs. A
Monte-Carlo simulation technique may also be used where a statistical distribution is assigned to each of the inputs.

Section 4: Design Traffic Estimation
Page 52