Quieter Vehicles Research Articles

Quiet cars and blind pedestrians

People who are blind use traffic sounds to determine alignment, verify relative position to a street, identify their location, and decide an appropriate time to cross a street. With quieter vehicles, these pedestrians often do not have the amount or kind of acoustic information needed to make good, reliable travel decisions. Blind participants listened to internal combustion vehicles and hybrid vehicles (with and without added artificial sounds) approaching while moving forward, approaching while backing, and turning at an intersection. Participants indicated when they heard a vehicle and the direction of travel. Participants also aligned themselves to passing vehicles or indicated when crossable gaps between vehicles existed. Performance degraded most when ambient sound levels increased. However, even under extremely low ambient conditions, some tasks were not performed well. Some artificial sounds improved performance of particular tasks, but no artificial sound adequately enhanced performance in all tasks. Quieter vehicles have a potentially severe safety impact on pedestrians who are blind. Blind pedestrians may not be aware how their travel is impacted by less acoustic information. Addressing the impact by adding artificial sounds promises only a partial solution and should be augmented by other efforts.

On the hazard of quiet vehicles to pedestrians and drivers

The need to produce more efficient and less polluting vehicles has encouraged mass production of alternative energy vehicles, such as hybrid and electric cars. Many of these vehicles are capable of very quiet operation. While reducing noise pollution is desirable, quieter vehicles could negatively affect pedestrian safety because of reduced sound cues compared to louder internal combustion engines. Three studies were performed to investigate people's concern about this issue. In Study 1, a questionnaire completed by 378 people showed substantial positive interest in quiet hybrid and electric cars. However, they also indicated concern about the reduced auditory cues of quiet vehicles. In Study 2, 316 participants rated 14 sounds that could be potentially added to quiet alternative-energy vehicles. The data showed that participants did not want annoying sounds, but preferred adding “engine” and “hum” sounds relative to other types of sounds. In Study 3, 24 persons heard and rated 18 actual sounds within 6 categories that were added to a video of a hybrid vehicle driving by. The sounds most preferred were “engine” followed by “white noise” and “hum”. Implications for adding sounds to facilitate pedestrians' detection of moving vehicles and for aiding drivers' awareness of speed are discussed.

A survey of automobile wind noise.

The study of automobile aerodynamic noise is a field that has grown rapidly in the past decade. Automobile manufacturers and independent researchers now have a better understanding of the mechanisms of automobile aerodynamic noise. Methods of making wind noise measurements have been improved. Some fundamental wind noise reduction measures have been developed. In this paper, the basic mechanisms of automobile aerodynamic noise generation are explained. Current wind noise measurement instrumentation and techniques are reviewed. Some wind noise reduction measures found on today’s automobiles are discussed. Finally, a prediction method for an idealized case of automobile aerodynamic noise is shown. Knowledge of these advances will help automobile manufacturers to design quieter vehicles.

Reduction of community noise levels through effective vehicle noise legislation

Legislation limiting the noise emission of new and/or in-service vehicles has the obvious aim of reducing community annoyance caused by traffic noise, but the effectiveness of such legislation must be questioned. Firstly, the rank ordering of the noise levels emitted by different vehicles changes according to the particular vehicle operating mode specified for the test, yet most current legislation specifies only one operating mode which is itself of limited relevance to urban or highway traffic conditions. Secondly, there is still a wide discrepancy between the predicted lower traffic noise levels which should result from quieter vehicles and acceptable community noise levels. Thus, for the effective protection of a community against traffic noise, legislation should be extended to include at least the following: (a) the measurement of a vehicle's noise emission in several operating modes, (b) the restriction of vehicle movements with respect to routes and times, and (c) the provision of compensation to owners of adversely affected buildings so that the attenuation provided by their external envelopes may be improved.