56 | CONCRETO & Construções
level is only reached from approxi-
mately 75 km/h due to the greater
contribution of propulsion noise.
Aerodynamic sound only becomes
significant at very high speeds
(above 120 km/h). For electric cars,
the propulsion sound is almost to-
tally eliminated and the tyre noise
will be dominant, also at low speeds.
The graphs in Figure 2 pres-
ent the total A-weighted level of
both the rolling noise and propul-
sion noise components, as well
as the total sound power, as a
function of vehicle speed. The
curves show the linear relation for
propulsion noise and the logarithmic
relation for rolling noise. In addi-
tion, these relationships have been
established for constant speed on
a non-sloped surface. In practice
this means that in urban areas with
mixed traffic and a lot of accelerat-
ing/decelerating manoeuvres, the
influence of the pavement surface
and thus the rolling noise becomes
less relevant. Other measures in
the field of traffic management such
as speed limits and traffic flow con-
trol become of higher relevance in
those cases.
2.2 Interaction tyre-pavement
Of course, both the type of tyre
and the pavement play a role in
their mutual interaction. It should be
borne in mind that both elements are
not only designed with a low tyre-
pavement noise in mind, but first
and foremost, for good traffic safety
and a favourable price/lifespan ratio.
Various mechanisms are involved in
the creation of the tyre-pavement
noise generated by the interaction of
the tyres of a vehicle with the pave-
ment (hammer effect, air pumping,
‘stick-slip’ - and ‘stick-snap’). More-
over, the sound is further increased
by the ‘horn effect’, vibrations and
resonance.
2.3 How is traffic
noise measured?
In Europe, the Statistical Pass
By Method or the Close Proximity
Method are generally used.
With the Statistical Pass By
Method (SPB, ISO 11819-1), the
traffic noise is measured from the
side of the road for a large quan-
tity of passing vehicles, whereby a
distinction can be made between
u
Figure 2
Propulsion noise, rolling noise and total noise as a function of vehicle
speed for light and heavy duty vehicles ((VAN BLOKLAND et al. (2009))
u
Figure 3
Noise measurement with from left to right: SPB – CPX – OBSI (HAIDER (2010); AWV, Belgium;
RASMUSSEN (2008)).)
