New Zealand's public transport is constantly improving but still has a long way to go says Infrastructure NZ's chief executive officer. Travel Infrastructure Frailties

"I don't think it's good enough from a user perspective," said Stephen Selwood on Wednesday.

"We're constantly having to improve the system but any system like public transport where you're using one [train] line any disruption is going to cause problems," he told The AM Show.

Last week the derailment of a train in Wellington caused chaos for 20,000 commuters, and in June an electrical fault left all Auckland train services stopped dead in their tracks.