Not quite N gauge and it would need a big garden but what fun!
https://www.youtube.com/watch?v=mx9OmRWMIKQ (https://www.youtube.com/watch?v=mx9OmRWMIKQ)
Fascinating. Traction looks very good, too.
Here is a video (nothing to do with me) of a lap of the track at the local park, less than half a mile from me.
https://www.youtube.com/watch?v=HQGDm5CXU04 (https://www.youtube.com/watch?v=HQGDm5CXU04)
I actually helped build that track 40 years ago. It is dual 3-1/2" and 5" gauge and at the time was about 12' short of being the longest in the UK. The carriages are bogie mounted, and straddle the track, so driver and passengers are sat about 5" above the track, with their legs each side (a good position for driving). Each carriage has a manual brake, but only the front one has a handle inserted in the operating mechanism.
As for traction - a 5" gauge, narrow-gauge (0-4-2 IIRC) tank engine was once tested to see how much it could pull. At 15 ride-on carriages, each with 4 to 5 people (adults and children) on, they ran out of carriages!
I do have the full, running chassis of a 5" gauge Simplex 0-6-0 (nothing to do with the Simplexes known on real railways) that has been run on compressed air, but never got round to building the boiler.
That Britannia is superb!
There's a long thread on RMWeb of a guy building a 7" (IIRC) Flying Scotsman, I don't understand most of it, but the level of care and detail is breathtaking. Kudos to anyone who has the patience for that!