Page 19 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

3. DESIGN CONSIDERATIONS
There are many aspects to consider in the design process, before the actual pavement design can be performed.
This section discusses some of these considerations.

3.1 Road Category

In South Africa, roads are categorized according to the importance and level of service required. Table 2 gives
details of the four road categories used (TRH4; TRH12 and cncPAVE). The “approximate design reliability” is linked
to the category. Photographs of typical roads in each category are given in Figure 5.

For new design, the design reliability is usually introduced when estimating the structural capacity of a potential
design. This process is discussed in more detail in Theyse et al (1995 and 1996) for flexible pavements. For
rehabilitation design, the road category not only determines the approximate reliability for the future structural
capacity of the rehabilitated road, but also provides guidance on the percentile levels to use during the assessment
of condition data for the existing road.

Table 2. Definition of the Four Road Categories
Road Category
A B C D
Description Major inter-urban Inter-urban collectors Lightly trafficked rural
freeways and major and rural roads roads, strategic roads Rural access roads
rural roads
Importance Very important Important Less important Less important
Level of service Very high High Moderate Moderate
Typical Pavement Characteristics
Approximate design reliability 1
(%) 95 90 80 50
Length of road exceeding
terminal distress condition at 5 10 20 50
end of structural design life
0.3 – 10 million < 3 million < 1 million
Total equivalent traffic loading 3 – 100 million over 20
(E80/lane) years Depending on design Depending on design Depending on
strategy strategy design strategy
2
Typical pavement class ES10 – ES100 ES1 – ES10 < ES0.03 – ES3 ES0.003 – ES1
Daily traffic (evu) > 4000 600 – 10 000 < 600 < 500
Riding quality:
Constructed
IRI 2.4 – 1.6 2.9 – 1.6 3.5 – 2.4 4.2 – 2.4
Terminal
IRI 3.5 4.2 4.5 5.1
Rut level for flexible
pavements (mm)
Warning 10 10 10 10
Terminal 20 20 20 20
Area of shattered concrete for
3
rigid pavements (%)
CRCP and UTCRCP
Warning 0.2 0.3 0.4 0.5
Terminal 0.5 0.7 0.8 1.0
JCP and DJCP
Warning 2 3 4 5
Terminal 5 6 8 10
Note
1. Although 50% reliability is stated for Category D, this essentially implies designing for an average situation. Great caution
should, however, be taken when designing for an average situation with average values.
2. Traffic classes given in Section 4.1.5.
3. These criteria from cncPave.

Section 3: Design Considerations
Page 8