Making cars quiet is a pretty straightforward, if pricey, process these days. A little sound insulation here, some double-glazed glass there and you’re good to go.

Even the noise, or lack thereof, coming out of the exhaust pipes has been reduced to such low levels that some gas and even diesel-powered cars might as well be running on electricity, or not running at all.

In fact, when cruising down the highway the loudest sound created by a car is usually the tires rubbing on the road, something that can be more annoying for passersby than passengers.

To address this issue, the Wall Street Journal reports that a number of pilot programs are underway across the country build roads covered in so-called “quiet pavement,” with mixed results.

Far more involved than just laying down a fresh coat of concrete or asphalt, the trick is to find the right balance between the texture of the surface, its stiffness and porosity. For concrete, it’s the width and depth of the striations in the material that can be used to muffle the sound, while asphalt requires divots or some sort of negative texture, according to the Wall Street Journal.

One hurdle is that if these indentations become filled with debris they no longer have the same sound deadening effect and can actually make matters worse. In Europe, where these types of road surfaces are more common, giant vacuums are used to clean the streets.

However, when it’s successful, quiet pavement can reduce the sound of traffic by as much as 10 decibels, which is a significant improvement over the typical 65 to 75 decibel level of roadside noise.

Unfortunately, while the initial results are promising, tests in Washington state have found that the surfaces tend to deteriorate quickly and often become louder than standard surfacing, but officials tell the Journal they are undaunted in their quest and are currently experimenting with five different types of quiet concrete in different environments.

In the meantime, people who live near the highway might want to invest in a little sound insulation and some double-glazed windows…for their homes.