K2 horns are distinguished by two separate horn units, one of which is noticeably larger than the other. The horns may include a piece of metal mesh over the mouthpiece, to preserve the integrity of the unit. K2 horns can be mounted in a number of positions on locomotives. Railpower-brand locomotives feature two sets of K2 horns, for a total of 4 units, with a set on the front and the back of the train car.
K2 locomotive horns play a two-note interval, as each of the two units is responsible for contributing a single note. The Federal Railroad Administration determines the interval and volume at which the horns sound, with occasional exceptions. The K2 horn plays a minor third interval, sounding the notes D and F sharp. As long as circumstances permit, the notes are played between 96 and 110 decibels. The notes are sounded in a pattern of two long notes, one short and another long.
The RP20BD and RP20CD locomotives are classified as GenSet locomotives and manufactured by the company Railpower. GenSets are a green form of locomotive which have been shown to save up to 20 percent more fuel, compared to other diesel locomotives. GenSet systems are distinguished by being comprised of several generators and engines, compared to the single set of engine and generator found in most other locomotives. GenSet locomotives can significantly reduce pollution, though they are more expensive to produce.
The RP20BD and RP20CD GenSet locomotives both feature three engines and generators. The models feature a commitment to environmental conservation aside from the fuel-saving design, as they are built from salvaged parts. A major difference between the two types of engine is the number of axles, with the RPS0BD featuring four and the RP20CD six. The RP20BD is more predominant among the models, with 112 models under construction or in operation in North America. In contrast, there are only eight RP20CD models.
