A system that includes a vehicle horn can reduce noise pollution caused by vehicles. The system can include a vehicle horn that has a signal-based mode and a sound-based mode. In the signal-based mode, the vehicle horn can output an electronic signal. In the sound-based mode, the vehicle horn can output an audible signal. The system can select one of the signal-based mode and the sound-based mode for the vehicle horn based on the driving environment data acquired by one or more sensors. Upon receiving a horn command, the system can cause the vehicle horn to output a signal based on the selected mode.