Experimental Asphalt Sounds Better

WOODSIDE, Calif. — As it winds through this wealthy Bay Area community, the 280 Freeway offers a stunning vista of green rolling hills just east of the Pacific Ocean. Residents of Woodside say they pay a heavy price for living near the scenic corridor.

The highway has grown busier and noisier every year. Houses closest to it are often difficult to sell, even after they have been carefully insulated and equipped with outdoor fountains to mask the freeway roar.

“I have never had anyone tell me they want a home in a noisy area,” said Judi Kiel, a local real estate agent.

When residents deluged the state with complaints, Caltrans officials suggested a sound wall, Town Manager Susan George recalled. The community balked, saying the massive barrier would be unsightly.

After a letter-writing campaign, Woodside won a big concession two years ago: Caltrans agreed to repave a 2.6-mile stretch of 280 with an experimental, sound-absorbing asphalt.

Caltrans estimates that the $1.6-million project has reduced highway noise by six decibels. The typical sound wall provides an eight-decibel reduction for homes right next to a freeway.

“The noise is much better now,” said Daniel Yost, a lawyer who lives in Woodside.

The project used a material called open-graded asphalt, which has tiny pores. On a normal surface, pockets of compressed air form inside tire treads and the air makes noise as it escapes. The porous pavement reduces the air compression and thus the noise.

Another type of noise-reducing pavement is rubberized asphalt, which uses ground-up tires to create a porous surface. It also provides a way to recycle discarded tires, easing the load on landfills.

Caltrans engineers are concerned that the pavements may wear out faster than standard asphalt or concrete. In any case, pavement alone will not solve the long-term noise problem.

“If all the other trends keep going -- more traffic, wider freeways, more trucks, etc. -- you can’t keep ahead of the game with just quiet pavement,” said Paul Donavan, an acoustic consultant.