Clockwise upward staircases do actually have one advantage (in certain locales). Going upwards your forward travel distance is less than going downwards. This is assuming people generally walk on the right hand side. It just feels easier to traverse stairs as close to the inside as possible.
> It just feels easier to traverse stairs as close to the inside as possible.
I would expect that depends on the design of the spiral staircase.
In a spiral staircase, you want to go up about 3 meters in a 360° turn because you need a bit over 2m of headroom and some space for the stair itself.
That means that, 1m away from the center of the staircase, the slope will be about 50%. The ideal staircase has more or less “step width + twice the step height = 63cm” [1], so that would give a good step width of 31cm and a step height of 16cm.
However, 2m away from the center, that same stair would have a slope of about 25%, and the ideal step would be 41cm wide and 11cm high or thereabouts.
3m from the center you’d have a 16% slope, and the ideal step would be 45 cm wide, 8cm high, etc.
Now, in ‘standard’ designs [2], step height can’t change with distance to the center, so the designer has to pick one, and thus has control over the distance from the center where it’s easiest to step.
[1] https://www.practicalarchitecture.com/blog/the-geometry-of-a.... Of course, that’s a heuristic, and the ideal will be different for different persons, but what’s important is that simply scaling up a staircase in order to get wider steps is not a good idea.
[2] very wide stairs can and sometimes do have steps that are sloping upwards. I don’t think these are non-standard, but can’t think of a better word now.
I don't think spiral staircases generally get even 1m wide, it's not trivial for two people going in opposite directions to pass each other. You walk on the middle of the step as there isn't much room to the left or right to go to.
Also, in the context of “it just feels easier to traverse stairs as close to the inside as possible”, I think spiral staircases that are less than a meter wide aren’t relevant. On them, the only option is to walk in the middle of the stairs.
Actually more dangerous traveling downward on the inside, where a small misstep will have you miss 2-3 treads, as opposed to the outside where the same misstep won’t have you miss any.
I like this theory. Since most people are right-handed, and the right leg does more work than the left when walking up a counter-clockwise spiral staircase, it makes sense that spiral staircases would be designed counter-clockwise.
I don't think there was so much traffic on these stairs that you ended up forced to one side the whole way.
The forward distance travelled is also trivial in terms of effort compared to the height displacement upward. Most people can walk for 10 minutes without breaking a sweat, but way fewer would feel fine walking up stairs for 10 minutes.
Not to mention, you can simply have a convention that the downward walker on a spiral staircase favour whichever side is best.
