Investigating the effects of measured noise source heights on the predicted insertion loss of noise barriers in the new TNM software

At the present time the Federal Highway Administration is developing a new highway noise prediction model called TNM that is anticipated to be a superior model than its predecessor STAMINA 2.0. TNM will use frequency dependent measured noise source heights as a function of speed, acceleration, pavement type, road grade and vehicle class in its propagation loss and insertion loss calculations. Also, TNM will split the equivalent source height into two sub-sources at specified heights and calculate the insertion loss of noise barriers from these two sub-sources. The accuracy of this concept is investigated in this thesis, and it is found that on the average the two sub-source approach is less accurate than the single equivalent source approximation but will overestimate the attenuated levels, thus a conservative barrier height can be designed from this result.