Situations arise in which noise barriers are overlapped to accommodate highway entrance or exit ramps, service roads, local access roadways, underground utilities, or community desires regarding placement within the right-of-way. This arrangement of two parallel vertical barriers with an opening in between gives rise to the overlap noise barrier problem. The need to protect residential or institutional properties near the barrier opening led to the development of an analytical procedure to investigate the reflectiondiffraction effects of overlapping barrier designs.

In many highway noise barrier designs, breaks are introduced in othe1wise continuous noise barriers to accommodate entrance or exit ramps. Typically, a noise barrier along the highway is terminated at the ramp and then resumes on the service roadside, as shown in Figure 1. A break may be necessitated because of underground utilities or to provide access to shielded portions of the right-of-way. The presence of the break in an otherwise continuous noise barrier degrades barrier performance at receivers in the immediate neighborhood of the gap. To restore the integrity of the barrier, an overlap may be introduced to compensate for the presence of the gap. Problems that arise include how long the overlap should be and the amount of degradation due to the multiple reflection effect created between the overlapping barrier sections. The barrier overlap analysis procedure (BOAP) was developed to answer these questions.