Name a vehicle noise source, and it can be tamed. Road reflection from the underside of the motor? Enclose the motor, as did the London Transport Company. Noisy road surface? Use smooth asphalt. Aerodynamic noise? Design the body elements to reduce turbulence.
The automotive industry has at its disposal an incredible array of acoustic expertise. GM alone has about 100 men assigned to its acoustic research section, and headed until his recent retirement by David Apps, an international authority on automotive noise control. The Ford Motor Company has a noise-vibration-harshness research team whose job it is to cope with some 15,000 sound-producing components of a car. The quest is to eliminate some of these sounds, insulate others, and convert the stubborn ones into pleasing sounds for the passenger.
Even the cabs of trucks are being sound-insulated, because drivers and their assistants have been opting for quietness for radio listening and off-duty sleep.
But, let us remember that these noise-control efforts are primarily directed toward driver and passenger comfort, not toward the noise recipients outside the vehicle.
The American Trucking Association claims that methods and techniques for muffling truck exhaust are well known to truck manufacturers and that consequently there is no excuse for offending trucks to be coming off assembly lines.
Manufacturers can do more for quieter trucks than simply installing better mufflers. They can modify the design of air cleaners, fans, fuel injection and air intake systems. Mechanical noises from transmission and chassis could also be designed out.
The chassis GM used for New York City's garbage trucks was designed with more than a superior exhaust system. The engine itself was quieted by a number of innovations, ranging from a dry-element air cleaner to a five-blade, staggered configuration fan. The fan itself is enclosed in a shroud to reduce noise radiation from the engine housing. To purchasers of these quieter trucks GM recommended the use of tire treads designed to make less noise.
According to the motor vehicle manufacturers, the rubber tire manufacturers are slow to design less noise producing tires. To encourage both quieter tire design and quieter vehicle design, local governments could require lower speed limits for nighttime driving.
Motorcycle noise, in common with that of other motor vehicles, would be severely reduced if the public would ask for proper design, and enforce its demands in the act of purchasing. CQC proved this in December 1967. At a public demonstration the audience recoiled as a motorcycle was started up. The sound level meter read a hefty 110 decibels at 15 feet. The bike was stopped. When it was started up again, the observers heard only an astonishing muted purr: 70 decibels at 15 feet. A 40-decibel reduction. Why the difference?
In the "before" demonstration, the muffler had been removed. To control motorcycle noise a quality muffler is an essential. But so is quiet design. This motorcycle was unique in advertising that it was designed for quiet—and its claim stood up in demonstration.
Though difficult to accomplish in large cities, major arteries can be sited away from residential and other noise-sensitive areas, neighborhood traffic flow reduced by using bypass roads for through traffic, and the noise of stop-and-go driving eliminated by using cloverleafs and Y-interchanges. When all else fails, barriers can be placed between the roadway and the human target.
The Russians, to avoid traffic-noise problems in new towns, set up small models of building blocks representing residential, commercial, and industrial areas. Tests are conducted to see how simulated traffic noise is to be kept from the residential area by using the non-residential buildings as barriers.
Other methods for reducing the amount of noise radiating from the road include depressed road construction, the use of flanking barriers, and covering the surface with plastic materials that absorb tire noise.
Chicago has built "groove ways" or depressed roads for its highway from the Loop to O'Hare Airport. When it is not feasible to depress a roadway, planners can try high shoulders, with landscaping. The Russians are experimenting with barriers on expressways in new city districts. These barriers are earth banks three meters high along each side of the road, terraced down to the buildings and topped with reinforced concrete screens. The topping will be planted with trees.
Architect Morris Ketchum points across the Atlantic to Cumbernauld, a new town in Scotland, where the city and traffic live together in harmony. Its center expressway is depressed and framed by earthen banks. Shopping, offices, and theaters all border this main street. Most of the residential buildings are set at right angles to motorways so that sound cannot reverberate among them. "It is a quiet city."
Recognizing the difficulty of reducing the daily din of life, towns in Austria, Germany, France, and Switzerland have instituted "quiet zones" in which vehicular traffic is verboten during certain hours of the day and night. An example is France's Vittell Thermal Spa. In response to many complaints about traffic noise, and to protect the peace of summer vacationists, a Quiet Zone was created within the thermal bath quarters. Traffic of all motor vehicles—including motorcycles—is prohibited between 10:00 P.M. and 7:00 AM. After 10:00 P.M. access to the main part of town, which houses the major hotels, is achieved via roads that lead to large parking zones, which are situated close to the hotels. Newcomers entering the town are informed of the regulations. Enforcement has been no problem.
The ramifications of this "quiet zone" should give the auto industry pause. Here is a case in which society says it will not bother with methods of reducing noise, but will eliminate it by banning the source.
Attempts to curb auto horn blowing began soon after the first horn was blown. The curse of the horn is worldwide, and so are the legislative attempts to lift it.
There are several approaches available today for curbing this irritant. Limits on the intensity and tonal quality can stimulate design of an auto horn that emits pleasing tones, with upper limits set for loudness.
The need for horn blowing can be reduced by substituting an overtaking or passing light system. A special position on the direction-signal switch arm activates head lamps as an effective signal in the daytime. At night, in place of sound signals, the use of such anti-dazzling lights at short intervals is relied on. Austria, for example, minimizes the need to use a horn by requiring that automobiles be equipped with an optical device that flashes intermittently, but without any dazzle. This type of special passing light system is illegal in the United States.
Paris is the pioneer in horn control. Sometime before 1930 the Prefect of Police there made use of horns unlawful after midnight:
Drivers are compelled to slacken the pace of their vehicle everywhere needed, in particular at crossroads, so as to make it useless to use a horn.
Art. 2—Infractions of the provisions of this ordinance will be recorded in orders to pay a fine which will be forwarded to the competent courts.
Drivers learned that they could operate as safely without acoustic warnings as with them, and grew to rely on the auto horn less during the day, also. It was natural that the ban would then be extended (1954) to daytime driving as well.
New York followed Paris in enacting an anti-horn blowing ordinance—one more respected in the breach than in the observance, and one the police seem to enforce in ten-year cycles.