Is it legal to put a train horn on a car?

Real train horns, and how loud they are

Real train horns are set by federal rule. The Federal Railroad Administration requires the horn on a train’s lead locomotive to produce at least 96 and no more than 110 A-weighted decibels, measured 100 feet in front of the locomotive. Federal rules also set how it is sounded at a public crossing: two long blasts, one short and one long, starting 15 to 20 seconds before the train reaches the crossing and repeated until it arrives. A train going faster than 60 mph may not start more than a quarter mile out. Aftermarket train horn kits are sold to bring that kind of sound to cars and pickup trucks.

FRA explained the ceiling in a 2003 interim rule. Many commenters believed train horns were too loud, and the agency concluded that 110 decibels should be enough to alert motorists in most situations.

For a sense of scale, the National Institute for Occupational Safety and Health sets its recommended workplace noise limit at 85 decibels averaged over an eight-hour day, and recommends cutting exposure time in half for every 3-decibel increase. The National Institute on Deafness and Other Communication Disorders says long or repeated exposure at or above 85 decibels can cause hearing loss, and lists normal conversation at 60 to 70 decibels and sirens at 110 to 129. A locomotive horn’s required range, even measured 100 feet away, is well above the 85-decibel line.

Sources: 49 CFR § 229.129, locomotive horn (Cornell LII) · 49 CFR § 222.21, when a locomotive horn must be used (Cornell LII) · Federal Register, Dec. 18, 2003: FRA interim final rule, Use of Locomotive Horns at Highway-Rail Grade Crossings (68 FR 70586) · NIOSH: Understand Noise Exposure · NIDCD (NIH): Noise-Induced Hearing Loss

Why trains sound their horns at crossings

The federal horn rule grew out of a Florida experiment. Starting in 1984, Florida let local governments ban nighttime train whistles on intrastate railroads at crossings equipped with gates, flashing lights and warning signs. When FRA studied the results, it found that nighttime collisions at affected Florida East Coast Railway crossings rose 195 percent after the bans took effect, compared with 67 percent at similar crossings on a parallel CSX line that was not covered by the bans. FRA ordered an end to the Florida bans in July 1991.

Congress followed in 1994 with a law directing the U.S. Department of Transportation to require a horn as each train approaches a public crossing, while allowing exceptions where the risk is not significant or other safety measures make up for the missing warning. FRA’s rules turned those exceptions into quiet zones: stretches of track, generally at least half a mile long, where horns are not routinely sounded. Crossings in newly created zones generally need flashing lights, gates and signs. In its 2003 rule, FRA reported that 2,140 people died in crossing collisions from 1997 through 2001, and that a collision with a train is 40 times more likely to kill someone than a crash between two highway vehicles.

Sources: Federal Register, Dec. 18, 2003: FRA interim final rule, Use of Locomotive Horns at Highway-Rail Grade Crossings (68 FR 70586) · 49 U.S.C. § 20153, audible warnings at highway-rail grade crossings (Cornell LII)

Why most states say “Allowed with limits”

State horn laws are strikingly similar because many of them trace back to the same model. The Uniform Vehicle Code, first published in 1926, was written as a guide for state legislatures. Its 1968 edition requires a horn audible under normal conditions from at least 200 feet, says that no horn “shall emit an unreasonably loud or harsh sound or a whistle,” and bars sirens, whistles and bells except where the section allows them, mainly on emergency vehicles. Many of the state laws behind this map repeat that wording almost exactly. The code’s foreword argued that equipment rules needed substantial uniformity because vehicles are designed for use anywhere in the country, and a 1971 review of state horn laws by the National Highway Traffic Safety Administration found virtually all states in substantial agreement with the code on requiring horns and limiting their use to when they are needed for safety.

The pattern holds today. In 42 states, a statute or inspection rule requires a horn that can be heard from 200 feet, and 40 states use the phrase “unreasonably loud or harsh.” In most of those, the phrase limits the horn itself. In nine, including Alabama, Delaware, Oregon and Virginia, it limits how a driver sounds the horn instead.

Almost none of these laws mention train horns or air horns by name. In most states, then, the question is whether a particular horn is “unreasonably loud or harsh,” and the law leaves that to judgment instead of setting a decibel number. A horn built to sound like a locomotive is likely to fail that test, and many state answers on this map say so, but none of those states draws a bright line.

A few states stand apart. Hawaii’s inspection rules name “air horns (on small vehicles)” among the devices that keep a car from passing its safety inspection, which makes it the only state marked as banned. California allows only emergency vehicles to carry an air horn that breaks its loudness rule, and Michigan lists air horns only among the equipment allowed on emergency vehicles. At the other end, Maine, New Hampshire, and Vermont require a working horn but set no limit on its loudness or type.

Sources: Uniform Vehicle Code and Model Traffic Ordinance, revised 1968, § 12-401 (Public.Resource.Org copy) · NHTSA (1971), Horns: Traffic Laws Commentary (TRB TRID record)

California’s attempt at a decibel limit

In 2010, California lawmakers tried to put a number on “unreasonably loud.” Assembly Bill 2245 would have barred a car from carrying an aftermarket horn louder than 110 decibels, the same ceiling that applies to locomotives. The Assembly’s committee analysis said that figure is also typical of the average horn on a new car. The bill grew out of complaints about train noise in the author’s San Mateo County district. An FRA study in South San Francisco, Burlingame and San Mateo found the trains’ horns within the federal limit, and FRA staff told the author that aftermarket car horns had been identified as a possible factor in the complaints.

The analysis added that these horns imitate train horns and can confuse and endanger drivers and pedestrians. It noted claims that some reach 170 decibels, and pointed out that most traffic officers don’t carry sound-measuring equipment, which makes the “loud or harsh” standard hard to apply. The bill passed the legislature, but Governor Arnold Schwarzenegger vetoed it on September 24, 2010, calling it unnecessary because existing law already bars a horn from making an unreasonably loud or harsh sound. As of October 2026, California’s horn law still sets no decibel number.

Sources: California AB 2245 (2010), enrolled bill text · California Assembly Transportation Committee analysis of AB 2245 (Apr. 19, 2010) · California Assembly floor analysis of AB 2245 (May 2010) · Governor's veto message, California AB 2245 (Sept. 24, 2010) · Cal. Vehicle Code § 27000 (public.law)

Rules about using a horn

State laws also limit when a horn may be sounded at all, whatever kind it is. Missouri allows a horn to be used for warning purposes only. Massachusetts bars sounding a horn so that it makes a harsh, objectionable, or unreasonable noise. Vermont allows the horn only when needed for safety, and a separate Vermont law fines blowing horns that disturbs the peace between sunset and sunrise.

Some states add their own twists. Oklahoma makes it illegal to use any sound device that mimics an emergency vehicle or makes other drivers yield and stop, and since 2021 it has barred honking when passing a bicyclist or horse rider unless a crash is imminent. Michigan lets vehicles with historic plates use a siren, whistle or bell at parades and similar events, and Oregon exempts antique vehicles used for shows and parades from its equipment rules.

Penalties are set state by state. Florida treats a horn violation as a noncriminal traffic infraction, Ohio as a minor misdemeanor, and Oregon as a Class C traffic violation. Tennessee makes an unnecessary or unreasonably loud or harsh horn sound a Class C misdemeanor, and South Dakota a Class 2 misdemeanor.

So even in the states with the fewest equipment limits, the horn is meant as a warning device. Sounding it for other reasons on a public road can break these use rules even where the horn itself is allowed.

Based on the state records and sources in the table above.

Rules beyond the state answer

This map covers personal cars and pickups. Commercial vehicles follow a separate federal rule: the Federal Motor Carrier Safety Regulations require every bus and truck to have a horn in such condition as to give “an adequate and reliable warning signal.”

Some states tie their horn rules to periodic safety inspections. Hawaii’s inspectors may not certify a small vehicle fitted with an air horn, and Pennsylvania’s inspection rules tell inspectors to reject a vehicle fitted with a whistle or a device that makes an unreasonably loud or harsh sound. In those states a nonstandard horn can cause a failed inspection even if it is never sounded.

Sources: 49 CFR § 393.81, horn (Cornell LII)