Public transport use is soaring across Sydney, putting more pressure on crowded trains and buses.

An annual snapshot by the NSW Audit Office shows patronage across the public transport network increased by 12 per cent last financial year.

But the Audit Office also highlighted the failure of buses, in particular, to run on time. The report said buses operated by private companies "almost never" met punctuality targets for the middle or the end of their trips, while the government-owned State Transit bus operator "did not meet any punctuality targets during the year".

The Audit Office attributed the huge growth in passenger trips across Sydney – there were 72 million more public transport trips in 2015-16 compared to the year before – partly to the increased take-up of the Opal card.