From the Great Journey’s of New Zealand website:
We let the scenery deliver the thrills, and our huge panoramic windows and Open-air Viewing carriages bring New Zealand’s outstanding natural beauty to your seat. Meanwhile, the relaxed carriage atmosphere and local crew deliver that authentic, friendly, New Zealand charm.
Our Scenic Class carriages are designed to make everyone feel comfortable. So if you are travelling on our Northern Explorer, Coastal Pacific or TranzAlpine trains, with a wheelchair, powerchair or mobility scooter, then you can sit in one of our specially designed wheelchair spaces in the spacious and convenient Scenic Café carriage.
Further information is available on the NZ Train Accessibility page