Skip to Content

Why do backup alarms have to be loud?

If you’ve ever been around a construction site, you may be familiar with the high-pitched beeping or hissing noises coming from the work zone.

Those sounds come from backup alarms that alert workers to pay attention because a vehicle is reversing within the construction site. According to the United States Bureau of Labor Statistics, from 2003 to 2010, there were 962 workers who were killed at construction sites and nearly half of these deaths resulted from a vehicle or mobile equipment striking a worker. The large size of many construction vehicles and the large blind spots created by their size is a major part of this hazard.

In response to this long standing and recognized hazard on construction sites, the California Occupational Safety & Health Administration (Cal OSHA) requires that construction vehicles are fitted with backup alarms in order to reduce collisions between workers and these large vehicles, which unfortunately, are not rare in the construction industry.

“A significant fraction of fatal injuries at construction sites are due to workers being struck by a vehicle when it’s backing up,” says Ralph Sbragia, Construction Safety Manager for the Purple Line Extension Project. “Backup alarms are very important because workers are familiar with that sound and they know that it means they need to watch out for vehicles that may be coming their way.”

To properly serve its purpose and comply with state and federal laws, backup alarms are designed to be heard over other noises on a construction site (including local traffic) and in order to convey urgency to the workers, but the traditional high-pitched sound can be disruptive, even annoying, especially at night because this sound tends to carry long distances away from the worksite.

This has led to the development of low-impact alarms, which mimic the sound of a quacking duck.  These alarms use a broad band of sound frequencies rather than traditional single frequency devices, which makes the sound more tolerable and causes it to not carry great distances.

Metro Purple Line Extension Project is working with contractors and subcontractors to ensure that all trucks are fitted with these low-impact alarms for all night work. If a truck that will be used during night work is not properly fitted with the low-impact alarms, inspectors will immediately escort the vehicle off Metro’s project site.  Metro also continues to ensure that noise mitigation efforts like sound blankets and sound walls are being properly used.

Safety is always a priority during the construction of the Metro Purple Line Extension, but we also strive to be considerate neighbors and continue to work with the community while maintaining a safe work area.