I've always thought night trains are a fantastic, sustainable alternative to short-haul flights, but they're often held back by a lack of privacy, comfort, and poor economics due to low passenger capacity.
I became overly fascinated with this puzzle. I view it as a kind of night train Tetris (my wife less charitably calls it "sardinology"). I spent way too much time learning about and sketching various layouts, trying to figure out how to fit the maximum number of private cabins into a standard railcar, while making them attractive for both day and night travel.
This eventually led to a physical workshop (in Berlin) and a hands-on rapid prototyping process. We've built a series of full-scale mockups, starting with wood and cardboard and progressing to high-fidelity versions with 3D-printed and CNC-milled parts, with various functional elements.
Hundreds of people have come in to test our various iterations, because you can't test ergonomics or comfort by looking at renderings (although we did create a bunch of nice ones).
The link goes to our home page showing our approach and some of the thinking behind them. It’s been a lot of fun working on this puzzle, and we're excited to share what we've come up with. We hope you think it's cool too and would love to hear your thoughts.
The „long term“ concept is built around to be compatible with profiles UIC GB and G2, which work in most of Europe.
However the amount of demand there'd be for an overnight train from (let's just say) London to Barcelona at £99 each way would be immense.
As for intra-UK sleeper: yes there are some possible routes, but the market is small. Developing custom trains for that would be very expensive. And the concepts we propose don’t work well cut the profile is so small.
I wouldn't massively bother with intra-uk yet, I agree wholeheartedly.