Highway Pavement Materials and Design 203
7.4 Traffic loading,
When designing a new highway, the estimation of traffic levels at opening is
of central importance to the structural design of the upper layers of the road
pavement.
Of particular importance is the estimation of commercial vehicle volumes.
Commercial vehicles are defined as those with an unladen weight of 15 kN. They
are the primary cause of structural damage to the highway pavement, with the
damage arising from private cars negligible in comparison.
The following is the classification for commercial vehicles used in HD 24/96
(DoT 1996):
Buses and coaches (PSV)
2 axle rigid (OGV1)
3 axle rigid (OGV1)
3 axle articulated (OGV1)
4 axle rigid (OGV2)
4 axle articulated (OGV2)
5 +axles (OGV2).
These are illustrated graphically in Fig. 7.6.
In order to allow the determination of the cumulative design traffic for the
highway in question, therefore, the total flow of commercial vehicles per day in
one direction at the day of opening (or, for maintenance purposes, at the present
time) plus the proportion of vehicles in the OGV2 category must be ascertained.
If all flow data is two-directional, then a 50:50 split is assumed unless available
data demonstrates otherwise.
Figure 7.7 is a representation of the graph detailed in HD 24/96 for estimat-
Percentage passing by mass
CBM3/CBM4/CBM5
(40 mm nominal max Dry lean
BS sieve size CBM1 CBM2 size) concrete
75 mm 100 100 100 100
37.5 mm 95 95–100 95–100 95–100
20 mm 45 45–100 45–80 45–80
10 mm 35 35–100 — —
5mm2 5 25–100 25–50 25–50
2.36 mm — 15–90 — —
0.6 mm 8 8–65 8–30 8–30
0.3 mm 5 5–40 — —
0.15 mm — — 0–8 0–8
0.075 mm 0 0–10 0–5 0
Table 7.6Grading requirements of cement-bound and lean concrete materials for use in subbases
within both flexible and rigid pavements in the UK
