Drum brakes are way more prone to fail, the heat cant be transported away, the dust still is produced and the brake power, the law requires, is way to little. If we switch fully to trams and buses, they produce the dust amount of lets say 100 cars. If the public transportation should be capable of all inhabitants of a city, we would have up to 200 trams running every day and night. Who should be a tram driver? Most of the younger folks dont want to work shift or at weekends and night. My town has drivers with grey beards, between 50-60 years old. There are no younger applicants for that job so they drive even if retired to keep up the demand. They got paid extra which making tickets more expensive.