Hidden in an old warehouse near Sydney Olympic Park, a life-sized model of NSW's new intercity trains offers a glimpse into the future for passengers travelling to Newcastle, the Blue Mountains and the south coast.

For the past nine months, designers have been crawling over the stainless steel carriage – some of it made from 3D printing – to fine tune aspects of the interior such as baggage storage, bicycle racks and even the colour of seats.

Designers have been crawling over a life-size model of the new intercity trains at a warehouse near Olympic Park for the past nine months. Credit:Janie Barrett

The first of 512 new carriages will begin replacing the state's four-decade-old V-set trains from late next year on the rail line to the Central Coast and Newcastle.

By mid-2020, the new trains being built in South Korea will begin running on the Blue Mountains line to Mount Victoria, followed by Lithgow about four months later and, after that, on the South Coast line to Wollongong and Kiama.