INTO THE SOUND BARRIER

This article describes various initiatives to improve the quality of noise barriers for roads and railways. A recent meeting at the Transport Research Laboratory (TRL) indicated the need to adopt much more imaginative approaches. TRL itself has begun a research programme to examine the advantages and disadvantages of new types of noise barriers; it has constructed a facility for testing full scale noise barriers. In July 1992, the UK Roads Minister proposed that: (1) concrete road surfaces should not carry more than 75,000 vehicles a day; (2) there should be research on making them quieter; (3) porous asphalt should be used in noise-sensitive areas if it could be justified. It has been shown that appropriate barriers can reduce noise levels by more than 10dB, if placed near enough to the noise source. The European Standards Committee CEN TC225, on roadside equipment, is developing harmonised standards for comparing the mechanical and environmental performance, safety, long-term durability, etc, of devices for reducing road traffic noise. Noise barriers can be made from a wide variety of materials, and have five major configurations: (1) absorbing barriers; (2) shaped barriers to diffract or reflect sound; (3) parallel barriers; (4) barriers of vegetation rooted in earth mounds; (5) horizontal 'covers' over a road in a cutting. An Environmental Noise Barrier Association has just been formed.