Final answer:
The requirement for clear back up alarms on rubber tired units is dependent on local safety regulations and the Occupational Safety and Health Administration (OSHA) guidelines, which often mandate alarms for vehicles with obstructed rear views that are above a certain small vehicle exemption.
Step-by-step explanation:
The question pertains to the safety requirements for construction vehicles or equipment, specifically regarding the necessary inclusion of audible back up alarms for certain weight categories of rubber tired units. The exact weight at which a rubber tired unit requires an independent back up alarm can vary based on local laws and regulations. In general, Occupational Safety and Health Administration (OSHA) regulations often specify that these alarms are required for any vehicle that has an obstructed view to the rear and is not small enough to be exempt. It's crucial for workers on a construction site to be able to hear these alarms to ensure safety, as they signify that a large, potentially dangerous, vehicle is reversing.
To directly answer the question, an exact weight limit is not provided because it can differ depending on jurisdiction. For detailed local regulations, it would be necessary to consult specific workplace safety codes or OSHA guidelines. It's also worth noting that back up alarms are just one aspect of vehicle safety, with other factors including the visibility of the operator, training, and maintenance playing significant roles.