Both high-speed and bumper-to-bumper traffic can make living or working next to a modern expressway intolerable. In the search for silence, masonry noise barrier walls are becoming commonplace in traffic-snarled cities like Los Angeles. In many areas, whenever a new expressway or expansion is built, noise barriers must be included as part of the project. Thus this growing market is worth pursuing and promoting-by both masonry contractors and suppliers. BARRIER BASICS A noise barrier wall is the most common way highway departments reduce traffic noise. It reduces sound in three ways: it absorbs sound, it diffracts sound, and it reflects sound. The effectiveness of a noise barrier wall is determined by the amount of noise reduction that results. This is called "insertion loss." Measure the noise level without a barrier, insert the barrier, and measure the noise level again. The insertion loss is the difference in noise before and after the barrier. Insertion loss varies with the material, height, and design of the wall. THE MASONRY ADVANTAGE Masonry has many advantages for noise barrier walls: It's beautiful. It offers a wide variety of finishes and colors, both in concrete masonry and clay brick. A dense material, masonry provides good sound transmission loss and has no small openings that amplify sound. It requires little or no maintenance, is locally available, and in many places is cost-competitive.