by Doug Barrett
Last month I had the opportunity to make the 2.5 hour drive from Venice, Italy to Ljubljana, Slovenia. First rounding the broad lowlands of the northern Adriatic and then passing through the foothills of the Julian Alps, the Autostrada spans diverse cultures and landscapes. As one travels farther east, steeples in small towns change from Italianate towers to onion-shaped domes and the terrain transforms from coastal to mountainous.
While many visitors may focus on the centuries-old villages, ancient ruins, and timeless mountain vistas, the drive also offers quite a sample of modern highway noise barriers. My fabulous spouse not only tolerated, but (when I was driving) even contributed to a high-speed windshield survey of northern Italian and Slovenian noise barriers. Several features set these noise barriers apart from those typically found along highways in the United States:
Widespread use of sound-absorptive materials: Although some U.S. transportation agencies commonly use sound-absorptive materials to minimize the effects of reflected sound (Virginia DOT and New York State DOT come to mind), other state DOTs do not. Also, while cement-based absorptive materials are popular for highway barriers in the United States, metal panels were the most popular in this region.
Use of tilted noise barriers: Tilting noise barriers back from the highway is another strategy to reduce multiple reflections of sound between parallel barriers. This technique, although rare in the U.S., was common here. Sometimes entire barriers were tilted, other times, each individual panel, or just the upper portion of the barrier was angled.
Transparent materials: In some locations, scenic views were preserved by using transparent panels. On many barriers, only the top portion was transparent, typically with the obligatory hawk decal to reduce bird strikes.
I found the mixing and matching of these features to be especially interesting. Because the transparent materials are not sound-absorptive, often they were paired with sound-absorptive lower panels. In some cases, only the transparent upper portion was curved or tilted. One barrier included a sound-absorptive lower section combined with a transparent upper section, bent towards the road to increase the barrier’s effective height. The entire structure was capped by a sound-absorptive roll-top, also intended to improve the barrier’s noise reduction benefit.