ANALYSIS AND PROGRAMS FOR ASSESSMENT OF ABSORPTIVE AND TILTED PARALLEL BARRIERS

An analysis and a computer program were prepared for use in connection with a FHWA test program. As part of this procedure, a model based on ray theory was developed for the prediction of highway traffic noise in the presence of tilted, absorptive barriers that are parallel to the roadway. The model was programmed for use on a personal computer or other DOS-compatible small computer. The program, called Barrier X, uses impedance of the barrier surface as input to compute the barrier reflection coefficients, which are therefore angle dependent. The program accounts for the modification of barrier reflection due to diffraction at discontinuities of the barrier surface impedance and at the discontinuity at the upper edges. Effects of atmospheric absorption, terrain absorption, and the pavement-wayside impedance discontinuity are taken into consideration. The highway and barriers are assumed to be straight and the wayside flat, but otherwise the program inputs permit considerable flexibility. Preliminary computations made with the program are in agreement with other recent studies, which conclude that parallel reflective barriers can severely reduce the anticipated single-barrier insertion loss and that absorptive wall treatment can be very beneficial. A result of considerable interest is that in roadway geometries of interest, relatively small angles of tilt can restore almost all of the single-barrier insertion loss.

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