The Federal Railroad Administration requires train volume between the maximum of 110 decibels and the minimum of 96 decibels. The train engineers are required to sound two longs, one short and one long blast (- – · -) on the horn a quarter mile before entering a grade crossing.
While still in compliance with federal law, Caltrain has reduced the horn volume that can be heard in the community by mounting the horns under the trains rather than on top and set the horns at the minimum required volume.
Communities wishing to further reduce or eliminate horn noise can pursue Quiet Zone or install stationary horns. Stationary horns are still required to produce horn volume that meets the federal law, but can be directed towards oncoming traffic rather than a wider area.