Lexus LS 600h L, the Mercedes S350 CDI and the BMW 335d coupe are some quiet cars, as of 2016. While there is no car whose running engine does not produce at least some noise, some electric, hybrid and diesel cars have engines that work at lower revolutions, leading to less noise.
The diesel powered Mercedes S350 CDI produces only 63.3 decibels, making it extra quiet. It comes fitted with an automatic transmission that disengages as soon as the brakes are hit, and the car stops fully. Additionally, it has rather low emission levels and very good fuel economy. The hybrid Lexus LS 600h L sedan also has noise levels of 63.3 decibels. It is fitted with two electric motors and a 5.0-liter V8 engine.
The BMW 335d coupe is also quite a silent performer with its twin-turbo 3.0-liter diesel engine with 290 horsepower. Quiet cars operate at lower speeds in the absence of an internal combustion engine running. Pending U.S. rules may make quiet cars louder, with a proposed requirement for these cars to add new audio alerts at low speeds. Hybrid and electric vehicles traveling at or below 18 miles per hour may have automatic audio alerts added to them if this rule is implemented.