An Investigation of Temporary Threshold Shift and Noise Dose in Contemporary Commercial Trucks

The Federal Highway Administration (FHWA) currently requires that individuals seeking a commercial driver's license for interstate commerce possess a certain minimal level of hearing. Past studies have shown that truck noise (in certain older vehicles, at least) is loud enough to cause permanent hearing damage if experienced for sufficient durations. There have also been reports that truck drivers have indeed suffered hearing loss, possibly due to their noise exposure. As part of an overall evaluation of the FHWA hearing requirement, pre-and post-workday audiograms were performed on 10 truck drivers to determine whether they suffer a temporary threshold shift (TTS) at the end of the work shift. Dosimeters were used to measure the noise dose for the same 10 drivers. Ten different trucks were used; although the trucks were from three homogenous manufacturer groups, the truck mileage, cargo, and weight variables demonstrated considerable randomness. The results showed that there was no evidence of a TTS among these 10 drivers and that the noise doses experienced by these drivers were all within a range considered safe by OSHA. However, an analysis of pre-work audiograms for 30 truck drivers showed some evidence of a noise-induced permanent threshold shift, when these drivers' audiograms were compared to those of a similar age/gender non-noise exposed population.