Noise pollution
Noise is pollution, and in a Nepali city the horn is its largest single source.
Sound the horn only as a warning. It is prohibited near schools and hospitals and around gatherings, and restricted across many urban areas.
Modified or unusually loud silencers are an offence. A silencer removed or replaced to be louder makes the vehicle both noisier and dirtier.
Engine noise and repeated hard acceleration in built-up areas count too. Steady driving is quieter as well as cheaper.