Seattle Municipal Code (SMC) 11.52 establishes speed regulations; SMC 11.16.120 authorizes the SDOT director to set speed limits.
Seattle Municipal Code (SMC) 11.69 allows the Chief of Police to declare all or a portion of a street or way open to the public to be a "traffic congestion area" under certain conditions, such as the average vehicle speed slowing to less than one-half the posted speed limit. If so designated, passage of a motor vehicle more than one (1) time in the same direction within a four (4) hour period is a violation of law.
SMC 25.08 Subchapter IV regulates Motor Vehicle Sound Levels
SMC 11.84.080 requires that:
"Every motor vehicle shall at all times be equipped with a muffler in good working order and in constant operation to prevent excessive or unusual noise and no person shall use a muffler cut-out, bypass or similar device upon a motor vehicle on a street or alley."
SMC 25.08.450 states that "No person shall modify the exhaust system of a motor vehicle in a manner which will amplify or increase, the noise emitted by the engine of such vehicle above that emitted by the muffler originally installed on the vehicle, and it shall be unlawful for any person to operate a motor vehicle not equipped as required by Sections 11.84.060 and 11.84.080 or which has been amplified as prohibited by this section."
SMC 25.08.460 states "It is unlawful for any person to operate a motor vehicle in such a manner as to cause or allow to be emitted squealing, screeching or other such sound from the tires in contact with the ground because of rapid acceleration or excessive speed around corners or other such reason, provided that sound resulting from emergency braking to avoid imminent danger shall be exempt from this section."
SMC 11.84.060 requires brakes to be maintained in good working order, and requires that a motor vehicle equipped with a device that uses the compression of the motor vehicle engine shall not use the device unless the vehicle is equipped with an operational muffler and exhaust system to prevent excess noise.
SMC 25.08.515 establishes noise limits for vehicle sound systems in residential and commercial zones; the content of the sound cannot be used to determine a violation.
SMC 11.22.080 requires the display of license plates on the front and rear of motor vehicles.
SMC 11.84.150 establishes standards for applying tinting or coloring materials to windows, and prohibits operating of vehicles in violation.
No City of Seattle Law prohibits idling; Boise established a "be idle free" education and sign campaign. Salt Lake City and Ann Arbor have passed laws limiting idling.
A new law passed by the state legislature in 2017 creates an infraction for "dangerously distracted driving" (RCW 46.61.473) as a secondary infraction, and a prohibition on the use of electronic devices while driving (RCW 46.61.672).