49 CFR 325.7: Allowable noise levels.

Motor vehicle noise emissions, when measured according to the rules of this part, shall not exceed the values specified in Table 1.

Table 1—Maximum Permissible Sound Level Readings (Decibel (A)) 1 2

Highway operation test Stationary tests

Soft site Hard Site Soft site Hard site

35 mi/h or less Above 35 mi/h 35 mi/h or less Above 35 mi/h

If the distance between the microphone location point and the microphone target point is—

31 ft (9.5m) or more but less than 35 ft (10.7m) 87 91 89 93 89 91

35 ft (10.7m) or more but less than 39 ft (11.9m) 86 90 88 92 88 90

39 ft (11.9m) or more but less than 43 ft (13.1m) 85 89 87 91 87 89

43 ft (13.1m) or more but less than 48 ft (14.6m) 84 88 86 90 86 88

48 ft (14.6m) or more but less than 58 ft (17.1m) 83 87 85 89 85 87

58 ft (17.1m) or more but less than 70 ft (21.3m) 82 86 84 88 84 86

70 ft (21.3m) or more but less than 83 ft (25.3m) 81 85 83 87 83 85

1 The speeds shown refer to measurements taken at sites having speed limits as indicated. These speed limits do not necessarily have to be posted.

2 This table is based on motor carrier noise emission requirements specified in 40 CFR 202.20 and 40 CFR 202.21.