A Wellington resident whose home sits within metres of the Johnsonville line says it is time the city's commuter network had the safety upgrades that have been talked about for a decade.

Six people were injured on Saturday night when a Metlink train ran a red signal leaving Khandallah Station and collided with a concrete block at the end of a short diversion track. Photos from inside the cabin showed extensive blood and twisted metal.

Buses are replacing trains between Wellington and Johnsonville until at least Wednesday while the Transport Accident Investigation Commission examines the wreckage. Investigators said on Sunday it was "too early to say" what caused the train to overrun the signal.

Khandallah resident Patrick Yeo, who lives at the boundary of the rail corridor, said it had taken a serious incident to draw attention to a line that locals describe as ageing and brittle. "We've had cancellations, we've had near-misses. Now we've had this."

Greater Wellington Regional Council chair Daran Ponter said an accelerated signalling upgrade was already in the long-term plan, and confirmed the council would now "sit down with KiwiRail and ask whether the timeline needs to come forward."