That thing has already twice more doors than a train since the doors of both sides can be used, so it partially solves that problem already.
Not exactly. Longer stopping times are enough to get people off and on.
> How do you do that while keeping it structurally safe?
There are no possible structural issues. In fact, building this sort of bus is more trivial than a regular bus, as size and weight constraints aren't nearly as important as regular buses.
They also may be enough to annoy people so much that they will avoid this like the plague. Extreme example: if this loads and unloads like an airplane and makes a stop every few miles. Yes, maybe only 5% of passengers would get out and in at every stop, but that still would be a one minute stop every two minutes or so.
And if there are no structural issues, why do trains have so few doors nowadays? I would think stops could be a lot shorter at peak hours of trains had more doors.
That's a good point. I'm sure the bus operators programmed the bus' route to make it at least as good as regular trains with regards to the basic performance metrics such as average operational speed.
> And if there are no structural issues, why do trains have so few doors nowadays?
In short, design options. If a railway operator felt a demand for passenger wagons with more doors and a reduced number of seats, it would be trivial to design one. There are downsides to this (less seats, more moving parts, more maintenance, potentially heavier wagon, harder ticket control, etc...) but nothing stops anyone from doing a passenger car with doors everywhere.
In fact, this was already done in the past.
In practice there were half a dozen non-structural reasons to move to less doors including automatic doors being much safer, disabled accessibility and simply that those trains were cold.
Also: this thing being wider gives it about three times the floor area relative to a train, so it would require about thrice the number of doors to get passengers in and out efficiently. How do you do that while keeping it structurally safe? I guess the answer is that that spacious room inside would see a few walls added.