Abstract

Over the past 20 years, at least 25 fatal accidents in Québec have involved heavy vehicles backing up on construction sites, most often caused by a faulty back-up alarm. A preliminary study carried out for the regulatory committee on the Road Safety Code established an inventory of available knowledge on these alarms. Following this first phase, there was a need to examine the propagation of sound generated by back-up alarms on heavy vehicles used on construction sites and to propose a computerized model for predicting the safety of these devices. A field study was then conducted on the different types of heavy vehicles equipped with back-up alarms. The data collected was used to develop a computerized model of sound propagation that takes into account the complex reflection and refraction behaviour of sound waves behind various types of vehicles. These interference phenomena produce major variations in sound pressure levels about a dozen centimetres behind the vehicles. These variations can mislead workers, by making the signal inaudible when the background noise is intense, or by creating the impression that the vehicle is moving further away, when the opposite is actually occurring. With this software, it is now possible to identify today’s commercially available back-up alarms that do not meet minimum safety standards.