FHWA/IN/JTRP-2001/19 Final Report NOISE CONTROL AND SPEECH INTELLIGIBILITY IMPROVEMENT OF A TOLL PLAZA

The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Indiana Department of Transportation of the Federal Highway Administration at the time of publication. The report does not constitute a standard, specification, or regulation. Vehicular toll roads are one component of many municipal transportation systems. Open communication windows, often used in tollbooths, facilitate essential communication and monetary transactions. However, the vehicle noise generated outside the booth is easily transmitted into the booth via the open window. Personnel working at toll collection plazas are exposed to extended, continuous traffic noise. Sustained noise levels of this nature may cause hearing loss, induce fatigue or stress, and reduce worker productivity. The annoyance and discomfort related to continuous noise exposure may create an unpleasant working condition and may affect the hospitality of the tollbooth operators and their attitude toward customers. Furthermore, the noise level may hinder communication with customers and may compromise safety. Reduction of the noise level and an improvement in speech intelligibility are highly desirable. The acoustics of a typical toll plaza and structural noise control strategies were modeled using a beam tracing technique. Noise control strategies involved the application sound absorbing material to the overhead canopy, the construction of sound absorbing partial barriers, and the treatment of tollbooth walls with sound absorbing material. In terms of noise control, the results suggest that the direct field is more important that the reflected field. The effects of active noise control (ANC) systems to reduce traffic noise and improve speech intelligibility at the toll plaza was investigated. The ANC systems included a range of headsets and a prototype external unit designed to create a local region of attenuation. Significant noise reduction can be achieved with a sealed, closed ear ANC headsets. However, the various systems seemed to have little positive effect upon speech intelligibility under traffic noise conditions. The result imply that the signal to noise ratio under toll plaza conditions is poor and that level overloading effects may further reduce intelligibility. Altered systems were modeled to improve the signal to noise ratio and reduce the noise level. The improved systems utilize a directional microphone and a sealed ANC headset. With a high order directional microphone, good speech intelligibility is achievable even in the presence of …