Summary

New technology for heavy vehicle reverse alarms has recently appeared on the market. According to the manufacturer, this technology, based on the use of a broadband signal (shh…shh…shh signal), is safer for workers and causes less noise pollution than the conventional tonal alarm (beep…beep…beep signal). However, it is difficult to say whether this technology is better, because of the paucity of independent and rigorous scientific studies on the subject.

This study compared the new broadband alarm technology with conventional alarms from the standpoint of worker safety. Two sets of trials were carried out to make the comparisons. In the first, a field trial, the sound propagation fields generated by the alarms behind heavy vehicles were measured to study their uniformity under conditions similar to those found in the workplace. In the second, human participants carried out psychoacoustic tests in the laboratory. They performed tasks related to alarm perception (detection thresholds, equal loudness, perceived urgency and sound localization).

Through an analysis of the alarm signals, the broadband alarm was deemed compliant with the SAE J994 standard, which is the standard most commonly used to certify alarms installed on heavy vehicles. In addition, the overall results of both field and laboratory trials did not reveal any contraindications to the use of the broadband reverse alarm with respect to worker safety. This type of alarm provides a much more homogeneous sound field behind vehicles and is easier to locate spatially, particularly in the front/rear dimension. The potential advantages of a tonal alarm (better detection under noisy conditions and a slightly greater sense of urgency conveyed in certain situations), would probably not overcome the adverse effect of major spatial variations in sound levels found over short distances behind a vehicle with this alarm (on the order of 15 to 20 dB), which are noticeably more pronounced than those generated by the broadband alarm.

In this report, the effect of parameters such as ambient noise, the use of hearing protection devices (HPD), and the type of protectors worn (ear muffs versus earplugs) on psychoacoustic indicators is presented for both alarm types. Finally, recommendations have been formulated to ensure the optimal use of broadband alarms, and important aspects requiring more extensive investigation are identified.