Other states reported vandalism problems, and, in a few cases, arson. Information from the survey about plastic and glass barriers was limited, since Maryland was the only state to report using these materials. The literature review revealed that lexan, glass, and fiberglass are the three main plastic or glass materials used in noise barriers. In particular, fiberglass is weather-resistant and durable, and it offers effective sound absorption and design flexibility. Several agencies reported using proprietary noise-barrier systems and absorptive treatments, a practice generally on the increase.
Landscape enhancements for noise mitigation are usually aesthetic rather than acoustical.
In those states where the public has been involved in barrier selection, citizens and property owners have tended to choose landscaping over a structural barrier. Design considerations such as color, texture, scale, line, proportion, and form must be carefully evaluated. This survey, like a 1981 predecessor, found that transportation agencies do not have enough data on the public's perception of aesthetically pleasing barriers, nor do they have enough money to satisfy perceived preferences. Transportation agencies are faced with the ongoing challenge of providing the public with a transportation system that is safe, cost-effective, and environmentally aware and responsive. Both transportation agencies and the public are becoming increasingly aware of the significance of aesthetics in relation to noise barriers.