You wanted to know the maximum allowable decibel level for motor vehicles and motor vehicle horns under Connecticut law.

SUMMARY

By state regulation, motor vehicles weighing less than 10,000 pounds that are manufactured after January 1, 1979 cannot exceed noise levels of 81 decibels (dB) when travelling more than 35 mph on a paved street or highway.

Decibel restrictions do not apply to sounds generated by a warning device, such as a horn or siren, installed in a motor vehicle. However, if the device is sounded in order to interrupt a noise emission test, the restrictions apply. The restrictions also do not apply to emergency vehicles responding to emergency calls, or snow plows in operation. (Conn. Agencies Regs. §14-80a-3a). Municipal ordinances may regulate permissible horn and siren levels.

STATE MOTOR VEHICLE NOISE LAWS

State law requires the Department of Motor Vehicles (DMV) commissioner, with the advice of the Department of Environmental Protection, to adopt regulations that establish maximum permissible noise levels for all motor vehicles.  The law prohibits (1) anyone from operating any vehicle above the maximum decibel level established for the vehicle, (2) an owner from allowing his or her vehicle to be operated in violation of these maximum noise levels, and (3) anyone from selling or offering a new vehicle for sale if it produces a maximum noise level that exceeds the level established in the regulations (CGS § 14-80a(a) and 80a(b)).

MEASURING DECIBEL LEVELS

The law authorizes the DMV commissioner to establish a procedure for checking maximum noise levels of vehicles.  These procedures determine acceptable decibel levels for a vehicle depending on the age, weight, current speed, and the road service on which it travels.

A decibel is the basic measurement unit for sound.  Decibel measurements are made on a logarithmic scale, which means that an increase of 10 dB approximates a perceived doubling of the noise level.  A noise source measuring 70 dB is therefore 10 times louder than a source measuring 60 dB and 100 times louder than a source reading 50 dB.  The average background noise in a typical home is between 40 and 50 dB.  State and federal motor vehicle regulations use the “dBA” scale of measurement, which is the scale that most closely approximates the sensitivity of the human ear.

Under DMV regulations, the noise level of a motor vehicle must be measured 50 feet from the centerline of the vehicle.  If the test procedure provides for measuring the noise from closer than 50 feet from the vehicle, the measuring devices must be calibrated in a way that creates an equivalency to measuring the sound at a distance of 50 feet.

Under the regulations, vehicles are divided into categories by their gross vehicle weight rating (GVWR), which is assigned by the manufacturer. It is the weight specified as the maximum fully loaded overall weight allowed for the vehicle. Vehicles may also be measured by their gross combination weight rating (GCWR). This is the sum total of the GVWR of each vehicle or unit comprising a combination vehicle.

Testing conditions are defined as hard or soft test sites. A hard test site is a test site with ground cover of concrete, asphalt, packed dirt, gravel, or similarly acoustically reflective material. A soft test site is a site covered with grass or other similarly absorptive material.

MAXIMUM NOISE LEVELS FOR MOTOR VEHICLES

The maximum permissible noise level for a motor vehicle manufactured on or after January 1, 1979 ranges from 72 dB to 92 dB, depending on the motor vehicle's speed, weight, and the road surface on which it travels. Tables 1 through 4 show the permissible noise levels of four classes of vehicles for different highway and road surfaces and for stationary operation.

Table 1 restrictions apply to most passenger cars. The maximum permissible noise level for a motor vehicle weighing 10,000 pounds or less ranges from 72 dB to 81 dB, depending on the motor vehicle's speed and the road surface on which it travels.  This is a lower range than both vehicles weighing 10,000 pounds or greater (86 dB to 92 dB), and motorcycles (78 dB to 84 dB) while operating. (These levels refer to highway operation.  Different levels apply to vehicles manufactured before January 1, 1979, and to stationary vehicles.)

Table 1: Maximum Permissible Sound Level for Motor Vehicles with a GVWR or a GCWR of 10,000 Pounds or Less

*Source: Conn. Agencies Regs. § 14-80a-4a

Table 2 shows the maximum permissible noise level for a motor vehicle weighing 10,000 pounds or greater ranges from 86 dB to 92 dB, depending on the motor vehicle's speed and the road surface on which it travels.  This is louder than passenger vehicles (72 dB to 81 dB), and motorcycles (78 dB to 84 dB) while operating. (These levels refer to highway operation.  Different levels apply to vehicles manufactured before January 1, 1979, and to stationary vehicles.)

Table 2: Maximum Permissible Sound Level for Motor Vehicles with a GVWR or a GCWR of 10,000 Pounds or Greater, Excluding Buses

*Source: Conn. Agencies Regs. §14-80a-4a

Table 3 shows the maximum permissible noise level for a motorcycle manufactured on or after January 1, 1979 ranges from 78 dB to 84 dB, depending on the motorcycle's speed and the road surface on which it travels.  This is louder than the maximum permissible noise level for passenger cars manufactured during the same period (72 dB to 81 dB), but quieter than the maximum permissible noise levels for vehicles weighing more than 10,000 pounds (86 to 92 dB). (These levels refer to highway operation.  Different levels apply to vehicles manufactured before January 1, 1979, and to stationary vehicles.)

Table 3: Maximum Permissible Sound Level for Motorcycles

*Source: Conn. Agencies Regs. §14-80a-4a

Table 4 shows the maximum permissible noise level for buses manufactured on or after January 1, 1979 ranges from 83 dB to 90 dB, depending on the buses' speed and the road surface on which it travels.  This is louder than the maximum permissible noise level for passenger cars (72 dB to 81 dB) and motorcycles (78 dB to 84 dB) manufactured during the same period, but quieter than the maximum permissible noise levels for vehicles weighing more than 10,000 pounds (86 to 92 dB). (These levels refer to highway operation.  Different levels apply to vehicles manufactured before January 1, 1979, and to stationary vehicles.)

Table 4: Maximum Permissible Sound Level for Buses with a GVWR or a GCWR of 10,000 Pounds of Greater

*Source: Conn. Agencies Regs. §14-80a-4a

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