PROBLEM $3$

The reference mean emission levels on a finite highway in a residential area are the following: Automobiles: $65$dBA, Medium$-$duty trucks: $75\mathrm{.}4$dBA and Heavy$-$duty trucks: $77\mathrm{.}8$dBA. The traffic flow adjustment factors for the automobiles, medium$-$duty trucks and heavy$-$duty trucks are $1\mathrm{.}2$dBA,$-8\mathrm{.}6$dBA and $-9\mathrm{.}7$ dBA, respectively. The distance adjustment factor is $-6\mathrm{.}1$dBA, and the finite roadway adjustment factor is $-2$dBA. Due to the high noise level, a noise barrier was proposed along the highway to reduce the noise that reaches to the residential area. As a result, the noise levels of automobiles and medium$-$duty trucks were each reduced by $9\mathrm{.}0$dBA, and the noise level of the heavy$-$duty truck was reduced by $5\mathrm{.}5$dBA. The FHWA specifies that the maximum mean sound pressure level $($SPL$)$ must not exceed $67\mathrm{.}0$dBA. Determine if the construction of the noise barrier satisfies the FHWA maximum SPL requirement. If not, what would be your recommendation?

Note: $SP{L}_{\text{t}\text{o}\text{t}\text{a}\text{l}}=10lo{g}_{10}{\displaystyle \underset{i=1}{\overset{n}{}}}{10}^{SP\frac{L_i}{10}},$ where $SP{L}_{\text{t}\text{o}\text{t}\text{a}\text{l}}=$ total sound pressure level, $SP{L}_i=$ sound ressure level of source $i.$