As an example of a source control, Thalheimer described new kinds of backup alarms that are more easily masked by background sources, can be about 20 decibels quieter than standard alarms, and are still readily audible behind the vehicle, as required by OSHA. OSHA also allows the use of vehicles without backup alarms if an observer directs the rearward motion of the vehicle. This is also an example of a tradeoff between introducing more risk to the contractor and public in exchange for minimizing noise.
The Park Service purchases and uses dozers, loaders, backhoes, generators, graders, dump trucks, jackhammers, rock drills, compressors, pumps, and rollers, and noise control measures are available for all. For example, anything with a diesel engine can have a muffler in good condition and a housing door that is closed. Jackhammers can use quieter bits or exhaust mufflers, and electric jackhammers are quieter than pneumatic, which are quieter than gas powered.
Path controls interrupt a noise between its source and a receiver. They include: