There I was in Las Vegas, Formula One cars in one ear and cement ready-mix trucks in the other. I thought for sure both of my eyes would be sifting through Sign Language for Dummies by now. My eardrums have been bludgeoned by race cars before, and here they were throwing heavy haulers into the mix. A few years ago I was touring the new Chicagoland Speedway and one of the ultrahigh-speed vehicles was cruising over some practice laps. I was able to get a front row seat of the powerful exhibition and quickly realized why noise protection is situated all over pit row. With each lap, I could feel each hair-like follicle deep inside my ear canal dying a painful death.
The press event at the Las Vegas Speedway, however, created dBA levels ideal for one of those Sharper Image sound machines. It was almost relaxing.
Transportation noise is usually not something which can put you to sleep, and pavement noise is one area that continues to receive spiked attention. Solutions are ongoing, and I thought I would share some of the breakthroughs unveiled at the Transportation Research Board (TRB) Annual Meeting in Washington, D.C., in mid-January. Since my ears continue to be functional and registered every bit of valuable information, I dedicate this effort of softening sound to them.
Thought to be the obvious solution, soundwalls have popped up everywhere along U.S. interstates where a community or subdivision sits close-by. Soundwalls do an ample job of deflecting decibels for those houses planted just beyond the barrier, and there is the added benefit of privacy from the chaotic movement of commerce. However, research shows that soundwalls fail to reduce noise levels to those who live down the block from a major interstate and neighborhoods on higher ground. Building noise walls higher is an option and could be effective, but cost becomes an issue.
Arizona was a haven of noisy pavement before it launched the Arizona Quiet Pavement Pilot Program, which is a $34 million project aimed at reducing highway-related traffic noise. The program is set to overlay most of the Phoenix metropolitan area with open-graded friction course asphalt (OGFC). So far, test results have shown that open-graded friction course asphalt has helped reduce levels down 7 to 9 dBA.
The state of New Jersey recently auditioned thin-lift hot-mix asphalt surface course mixes. For noise, OGFC generated the lowest levels. New Jersey also discovered two OGFC test sections which contained asphalt rubber performed the best of all, but also had the finest gradation.
Porous friction courses (PFC) appear to be another combatant of disturbance. When comparing PFC, Superpave and SMA at the North Central Superpave Center at Purdue University, the porous breed proved to be the superior product. According to results, Superpave and SMA pass-by noise levels were 5.9 dBA and 4.2 dBA higher, respectively. All three produced optimum numbers, but PFC came out on top.
Concrete seems to be adaptable to the quiet movement, too. In the Arizona study, whisper grinding (95.5 dBA) and longitudinal tining (99.1 dBA) were solid options. I saw the effects of longitudinal tining first-hand in Colorado and noticed a dramatic reduction in noise, and diamond grinding has been proven successful all across the country.
One common conclusion coming from all of the TRB presenters is that the older the pavement, the louder the noise. Do I hear another plea for increased maintenance in this country? It’s amazing what my abused ears can still pick up these days. But one point that came through loud and clear is the entire industry, covering both concrete and asphalt, is responding to a crescendo of chatter. It may take some time, but the race is on—and everyone will want to lend an ear to the results.