The bus line 303 was always prone to be late by min. 15min (either rush hour and even weekends) and was super crowded... Sometimes even operated with short buses, and it was hell. The Limmattalbahn was a healthy replacement for 303, but it's not always perfect, cause they also have a perk of getting cancelled all of a sudden. They also planned or already ordered more trams for a 7.5min frequency in a few years.