Green paternalists often gush about the great potential for hybrid electric automobiles to reduce negative externalities, or social costs, such as local air pollution and greenhouse gas emissions that result from driving. In addition to classic externalities such as crashes, congestion, and air pollution, excessive noise is also one form of social cost, albeit a relatively small cost -- remember the "whistle tipped" modified exhaust pipe video that went viral several years ago? The Federal Highway Administration has estimated that noise externalities average 0.06 cents per mile for cars and light trucks, while a paper by Mark A. Delucchi and Shi-Ling Hsu arrived at an estimated cost of 0-0.4 cents per mile. To put this in auto-externality perspective, crashes (which account for three-quarters of automobile social costs) average something like 15 cents per mile. The National Highway Traffic Safety Administration (NHTSA) is now moving in the opposite direction, and will soon begin a regulatory proceeding that will require that hybrid and electric vehicles emit sounds when they travel at low speeds (this would mean an audible alert whenever the vehicle is started and still stationary, in reverse, or traveling under 18 mph). Presumably, this is to benefit the blind, although NHTSA reveals in its own benefit-cost estimates that bicyclists will benefit more than pedestrians, and cycling is generally not a viable transportation mode for those with poor or no eyesight -- not to mention that cycling has a much smaller travel modal share than walking. To many, this would indicate that this isn't much of a problem in the first place and we live in a world of ever-changing risks best addressed by markets, but those who think as much generally don't opt for careers as government regulators or special-interest lobbyists. NHTSA has found that hybrid electric vehicles are more likely to be involved in certain pedestrian or cyclist accidents and says we can expect to save a few dozen lives nationally per year once the regulations come into full force (doubtful). So what do we know about pedestrian and cyclist fatalities when automobiles are involved? The vast majority of pedestrian or bicyclist injury events do not involve motor vehicles. Furthermore, in roadway accident settings, more than half of cycling and about one-third of pedestrian injuries do not involve motor vehicles -- meaning that the most serious threats facing many pedestrians and cyclists are their oft-inattentive selves. We also know that pedestrians and cyclists involved in accidents with motor vehicles are far more likely to be intoxicated than those involved in accidents without motor vehicles. It should not be surprising then that a disproportionate number of fatal accidents (as opposed to injurious accidents) involve intoxicated pedestrians and cyclists. These federally mandated noisemakers will likely do little to save drunk, stoned, iPod-listening pedestrians and bicyclists from their own stupidity inattentiveness. A small class of pedestrians and cyclists may certainly benefit at least initially, although regulation risks locking in inferior technology even once some better safety method or product is developed by automakers. But if we must have this silly nanny-state micromanagement, I hope our regulatory overlords have the sense of humor to make something like this the mandated hybrid alert sound. Unfortunately, NHTSA is not thinking very creatively about the sound possibilities.