The boundary element method has proven to be an important tool for the computational solution of many engineering problems. A commercial boundary element code was applied to traffic noise barrier analysis. First, it is shown that boundary element models may be used to quantify the accuracy of existing, approximate barrier models, for example, diffraction-based models. Diffraction-based models have been widely applied in noise control engineering applications owing to their relative ease of use. Recently, it was suggested that multipath diffraction components should be summed on a phase-coherent basis instead of on an energy basis. Here the accuracy of a phase-coherent diffraction model has been verified against the boundary element solution, showing limitations of the diffraction model. Second, the boundary element method was used to calculate a new barrier performance metric. In the past, the insertion loss has been considered the most important measure of noise barrier performance. However, insertion loss is normally defined at a particular receiver point in the shadow zone, and its value may vary significantly from point to point. The propagating sound power calculated on a recovery plane in the barrier shadow zone provides a more effective performance measure than does insertion loss when comparing the performance of different barrier designs.