"In 40 years of running lots of train services,you can never rule out disruptions occurring,"he said on Wednesday.
Mr Collins took charge of the city's rail network in 2013,when the O'Farrell government disbanded RailCorp and replaced it with Sydney Trains and NSW Trains.
The reorganisation of the transport bureaucracy over the past five years has meant his role as CEO is not as powerful as those held by his predecessors at RailCorp.
While Mr Collins is the public face of Sydney's rail network,much of the power now resides with Rodd Staples,the architect of the state government's metro rail plan,who replaced Tim Reardon as secretary of Transport for NSW last month.