OSHA regulations No employer shall use any motor vehicle, earthmoving, or compacting equipment having an obstructed view to the rear unless: * The vehicle has a reverse signal alarm distinguishable from the surrounding noise level, or * The vehicle is backed up only when an observer signals that it is safe to do so. 1926.601(b)(4)(i) &(ii) & 602(a)(9)(i)&(ii) from: www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=24943 (regarding a constituent's question as to whether "white noise" devices developed in Britain would be acceptable as alternatives to the piercing beeping noise now used here): ...we have neither the data nor the resources to evaluate whether this particular device would be "audible above the surrounding noise level" as required by the standard. If it does meet this test—that is, provides adequate warning to workers in the path of the vehicle, and to workers walking towards the path of the vehicle in time to avoid contact—it would comply with §1926.601(b)(4).