Page 54 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

1 �
HVV n
n
r = �� � − 1�
HVV 1 (12)

where r = Heavy vehicle volume growth rate (%)
HVV n = Heavy vehicle volume at year n
HVV 1 = Heavy vehicle volume at year 1

Table 17. Recommended Traffic Growth Rates Based on Historical Data for South Africa
Route Description and Economic Activity Heavy Vehicle Volume
Growth Rates (%)
Range Typical Long-
(pre 2007) term Values
Major routes connecting centres of major economic development 9 to 19 6 to 10
Routes connecting centres of moderate economic development 6 to 8 4 to 7
Routes in areas of stagnant economic development 0.5 to 1.5 0 to 2

TRH16 uses a technique developed by Bosman (1989 and 2004) to distinguish between routes with different heavy
vehicle compositions. Routes are classified according to the percentage of 2 axle heavy vehicles in the total HV
traffic. Although the extended vehicle classification does not separate out 2 axle heavy vehicles, the short vehicle
class should consist mostly of 1 and 2 axle heavy vehicles. Using the percentage of short heavy vehicles (SHV) as an
indicator of heavy vehicle composition, recommended E80/HV values are given in Table 18. These values should
only be used for new design, or, where there are good reasons for not conducting an axle load survey on an existing
road. The values are based on a damage law exponent of 4.2 and could be higher for more load sensitive
pavements (see Section 4.1.3).

Potential E80/HV growth rates are shown in Table 18. These growth rates only apply if the freight movement
demand increases on a route with an existing low or moderate freight movement demand, under normal overloading
control levels. The E80/HV at the end of the analysis period must not exceed realistic levels when using these
growth rates. Under strict overloading control, the E80/HV is limited by the legal axle loads and no growth occurs.
When the freight movement demand is high, with normal overloading control, the E80/HV is limited by the vehicle
capacity. Increases in demand are accommodated by increasing heavy vehicle volumes.

Table 18. Recommended E80/HV Values and Growth Rates for Heavy Vehicle Classes for
Design Purposes
Overloading control by Normal Strict
law enforcement
Freight movement Low Moderate High All levels
1
demand (SHV > 45%) (SHV = 20 – 45%) (SHV < 20%)
Heavy Vehicle Class Recommended E80/HV Values
Short heavy 0.5 – 1.5 0.4 – 0.8
Medium heavy 1.0 – 4.0 2.0 – 5.0 1.0 – 3.0
Long heavy 1.5 – 4.5 3.5 – 6.0 4.5 – 7.0 3.0 – 5.0
All heavy 0.8 – 2.8 2.0 – 4.5 3.0 – 5.0 2.0 – 3.0
Heavy Vehicle Class E80/HV Growth Rates
Short heavy 0
Medium heavy 3 0 0 0
Long heavy 5 2
All heavy 6 2
Notes
1. SHV = short heavy vehicle, 1 and 2 axle heavy vehicles

The heavy vehicle volume growth rate (Table 17) and the E80/HV growth rate (Table 18) are combined into a single
growth rate for the AADE using Equation (13).

Section 4: Design Traffic Estimation
Page 43