This provision is both an "objective emission" control and a "subjective immission" control with a curfew. It can apply to both public and private properties. Since these vehicles can move in large open areas, an "objective" control, limiting maximum sound levels at a fixed distance, is appropriate. Since they also can move in bounded areas near residences, a "subjective" control is appropriate. Numerous states and cities have "emission" controls measured at 50 feet; the most common level is 82 dB(A), which is similar to that for motor vehicles on public rights-of-way. Colorado Springs, CO (Section 9.8.204.C) requires a minimum distance of 660 feet from residences. Portland, OR (Section 18.10.020.C) requires the area must be designated for recreational vehicle use. Salt Lake health Department, UT (Section 4.5.10(x)) requires off-highway vehicles to be at least 800 feet from a dwelling during the day and has a curfew from 10 pm to 7 am. They prohibit any "noise disturbance" and require sound levels to the less than 96 dB(A) at 50 feet.