5. Conclusions
Through this study, the Leq(20 s) model suggested by
Pamanikabud [12] is improved theoretically and its rationality is
verified by the in-situ investigations. The following conclusions
can be drawn:
(1) The revision item for the finite length of road, 10 lgðD/
p Þ,
should be contained in the Leq(20 s) model, which can make
the model perfect and applicable for different conditions.
(2) Some deviations of Leq(20 s) model in theory were indicated.
When the vehicle speed ranged from 20 km/h to 120 km/h,
the deviation ranged from 0.80 dB(A) to 0.13 dB(A). Such
deviations were not significant but could be reduced easily
by revising the constant item 22.55 dB(A) in the model to
22 dB(A).
(3) A comparison of the real-time measurements of Leq(5 s)
with the calculations with the hypothesis of monopole and
dipole sources based on simultaneous measurements of
the maximum emission levels on roadsides indicated a mean
error of 1.2 dB(A) to 1.6 dB(A) for Leq(5 s) when the mean
energy emission level was employed in the FHWA model
for medium and heavy vehicles.
(4) When Leq(20 s) was considered the basic vehicular noise
instead of the mean energy emission level in the FHWA
model, the prediction accuracy of the model could be
improved.