Essentially, these standards require the use of specified muffler pipes. The effects of noise are subjective. Nonetheless, they can be significant. Short-term effects include startle reflexes and other effects relating to muscle tension, respiratory and circulatory responses. These can lead to heart attacks in extreme cases.
Headaches can result from successive short-term exposures to uncomfortable noise levels.
The most serious long-term effect is permanent or temporary hearing loss, the extent of which depends on susceptibility, duration of exposure, and noise intensity. Finally, noise can reduce enjoyment of live and recorded entertainment. There is no precise sound threshold for annoyance. In assessing the impact of transportation corridor changes it is difficult to separate the effects of noise changes from the effects of changed accessibility. This approach is not entirely accurate in that the relationship of added travel to total sound may be non-linear.