Designing for bangs, murmurs, and traffic noise

Even in sylvan settings, like here at Naumkeag, the added sounds of trickling water soothes strollers.

Even in sylvan settings, like here at Naumkeag, the added sounds of trickling water soothes strollers.

Designing a pleasant soundscape poses a greater challenge than creating a handsome view, but the rewards of lowered noise and enjoyable sounds are greater than those of visual harmony so sonic design is worth the extra effort.

Sonic design’s greater rewards derive from hearing’s being more visceral than seeing, as music proves by provoking stronger emotions than almost any painting. Hearing also retrieves sounds emanating from beyond our field of vision, extending our experience of space.

Sounds (or silence) can even define a place. Foghorns, waves on rocks, and wind through spruce trees place us on the Maine coast. The silence of moss and worn stones settles us into a meditation garden while one passage of the High Line through a building echoes with  the recorded sounds of bells from throughout the city establishing its specific urban context.

We can orient and wayfind by sound alone, as when gurgling, rustling grasses, and clattering whirligigs line a path for the blind.

Is the path ahead safe? A shout, a gunshot, the squeal of brakes—signal danger, whereas repeated, soft sounds of nature—birds twittering, water splashing, leaves fluttering—convey safety. Pleasant sounds, beyond being soothing in their own right, mask disruptive noise.

Removing traffic and its noise from areas of Times Square has attracted throngs almost any sunny day.

Removing traffic and its noise from areas of Times Square has attracted throngs almost any sunny day.

In today’s world, the most omnipresent, intrusive sound comes from traffic. “The noise from cars, motorcycles and most particularly buses and trucks ricochets between building façades, creating a continuously high noise level that makes it almost impossible to talk to others….,” reports Danish architect and urban planner Jan Gehl “Not only has any type of meaningful communication between people been rendered pointless, but the extreme noise level is also a permanent stress factor.”

Gehl reports that a background noise level of about 60 decibels (dBs) is the upper limit for normal conversation. Studies in a pedestrian town in the Venetian lagoon showed that quiet side streets averaged 52 dBs, a level that permits pleasant conversations at considerable distances, across canals, between people in the street, and between the street and people in buildings.

By contrast, studies Gehl Associates carried out in recent years on city center streets in London, Copenhagen, Sydney, and New York revealed noise levels between 72 and 75 dBs, twice to four times the level needed for casual conversations.

As a result of this understanding, an international design movement is growing to reshape urban centers to lower noise levels in order to attract more street life. Gehl himself has worked to lower noise levels in Copenhagen and New York among other cities to improve their street life. The most effective downtown noise controls involve minimizing traffic, lowering average traffic speeds, and creating traffic-free areas.

To minimize traffic, cities usually start by developing a comprehensive, fine-mesh transit system that is universally accessible and readily affordable. Follow-up measures include congestion fees for private cars and bike rental schemes. (See photos in The Importance of Walking in Cities.)

Traffic slows due to fewer, sometimes narrower, driving lanes; the nearness to parked cars or rows of trees; and longer-duration crossing lights for pedestrians.

Earth berms block road noise effectively but have a form and width most suited to suburban or rural areas.

Earth berms block road noise effectively but have a form and width most suited to suburban or rural areas.

Walkways can be insulated from remaining traffic noise by landform, walls, plantings, or distance, in descending order of effectiveness.

Earth berms are most effective and are feasible where space is available in rural and suburban areas. Sound-deadening walls are used along highways and consist of non-resonating material in isolated or gasketed layers.

Trees and shrubs can block traffic from sight, but it takes a continuous tree buffer 60 m/200 ft in width of fine foliage, like hemlock needles, to cut noise levels in half (lower by 10 decibels), whereas many-layered wooden walls can cut noise to an eighth or a thirty-second of the original level (lower by 25 to 50 decibels).

Walls are effective in narrow spaces, especially when gasketed.

Walls are effective in narrow spaces, especially when gasketed.

Barriers need to block the direct line between originating sound and listening ears. On level ground, most noise comes from tires meeting the road. On slopes, engine noise and truck’s engine brakes are added. In open areas, low barriers can suffice. In cities, low walls are less effective because sounds ricochet off tall buildings, so sound-deadening walls and windows are the optimal solution.

Lanes and parking spaces emptied of cars are filled with bike lanes and bike stands, widened sidewalks, esplanades with trees, and outdoor café seating. Unpleasant, dangerous car spaces become attractive people places.

Strollers and street performers return and congregate because listening and conversing are once again possible. Anyone who has revisited Times Square or almost anywhere in downtown London in the past few years knows how great an improvement in quiet and livability these kinds of measures have achieved.

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