Consider the following equation $($i$.$e$.,L_{10}),$ when an assessment point is moved from the position $r1$ to the position $r2($see the figure below$),$ what is the change of the total noise level due to the traffic noise of this road segment? For simplicity, we assume that both assessment point and effective noise source $($traffic flow$)$ are on the ground level. The effective noise source of traffic flow is represented by the dotted line in the figure. The lengths of the road segment and barrier are $720m$ and $240m,$ respectively. The positions $r1$ and $r2($located on the middle line$)$ are $60m$ and $80m$ away from the barrier, respectively.

Given:

$L_{10}(dB(A))=85\mathrm{.}0-10lo{g}_{10}(\frac{d}{13\mathrm{.}5})+10lo{g}_{10}(\frac{}{180})+C_b$

$d=$ direct distance between the source and the receiver $($m$)$;

$=$ angle of view $($degree$)$;

$C_b=$ barrier attenuation when the receiver is inside the shadow zone; and $0dB(A)$ when the receiver is outside the shadow zone$).$

$(5$ marks$)$