Train Horn Rules and Regulations
Train horns are specifically designed to be a loud warning at railroad crossings to prevent accidents. However, are they legal on other types of vehicles? The maximum legal decibel level for a car horn on a passenger vehicle is 100-110. A train horn has a decibel level of 130-150. As the train horn has significantly higher decibel level, what can be done?
All states have a line in their vehicle laws and regulations that states a car horn can not emit an unreasonably loud or harsh sound. Not all of them have that exact wording, but they all make the same point. However, some states make additional statements.
In California, a train horn can be mounted on a car but not used. On a semi-truck, it is allowed if it is attached to the air brake system, powered by the air from the brake system, complies with FMVSS standards 121 and 106, and has the appropriate certifications. If you are found to have violated those terms, you can receive a minimum $108 fine if there are no other violations or citations on your CDL.
In Texas, an annual inspection is required for all motor vehicles. If during the inspection, a train horn is found to be hooked up and able to be used as a regular warning, the vehicle will fail the inspection. It can, however, be hooked up on a truck as part of a commercial vehicle theft alarm. If the train horn is hooked up and used, you can recieve a citation for noise pollution and be held liable for any resulting accidents.
In Georgia the vehicle modification laws state that one could be used as part of an alarm system but not hooked up to be used as a regular warning system. Violation of this could result in a possible citation or moving violation.
Virginia law states that all warning devices must be approved by the Superintendent. A train horn could be used as part of an alarm or anti-theft system. However, it must be installed so that it cannot be used when the vehicle is in motion.
In most other states the only types of vehicles allowed to have any type of air horn are emergency vehicles.
To check the specifics in your area, check your state’s DMV or BMV website. Check laws specifically for horns, but also for vehicle modifications. A train horn would require an air compression system to operate, making it subject to the modification laws. Not all states have a law specifically prohibiting the horn being mounted on a vehicle, only the use of it as a standard warning device.