Mufflers for city buses

Been staying at daughter's place in DC, right off 14th St. It's noisy from the traffic. The cars are quiet, with only a slight hiss from the tires. The city buses are humungously loud, all from engine exhaust noise that a decent muffler would silence. Your car needs a decent muffler to get an inspection sticker. Cities would be pleasanter places if the inspectors got as tough on the buses as they are on private motor vehicles.