Sweeping Success Staircase ($2000), and A Stair to Remember by Smart Deco ($3150).
Do not use these stairs, the double ones with a flaring bottom, in a lot with many sims. I have had them in my dorms for years, and I and my sims have been constantly irritated by them. Though sims can cross on these stairs, only one sim at a time can go up each side, and only one sim at a time can go down each side. If six students arrive back from class with all of them in need of a loo and shower, only two can go up. The rest will stand at the bottom, stamping and waving and dropping the first item from their queue of actions. Similarly in the morning, when they are all ready for breakfast, the cries of outrage will ring through the dorm, as only the first two can go down to the refectory. For years I have adapted my play, sending two at a time to use the stairs, and holding back the others with chat and kicky-bag.

Then, for a change, I built into my new dorm two copies of the Virtually Unbreakable recolorable concrete stairs, side by side, and was delighted to find the whole dorm could walk up and down them sedately, with not one whine or stamp. The stairs lack the visual impact of the flaring staircases, but give more satisfactory play. Now, of course, I'm feeling foolish, for having put up with the nuisance for so long.

Well, that's all fixed stairs. Not just those two - all fixed straight stairs are like that. Spirals are a bit better. Modular stairs can have multiple people on them; that's why the concrete stairs are working, because they're modular.

I want to know if there are any object staircases made into modular ones?
Such a shame, so many look so nice, yet are horrible in routing quality.

@kasparlaks
I'd be happy with a mod that fixes that.

I believe it's to do with the mesh. With modular stairs each step is separate which is why when you download recolours you have to click and change each step one at a time. From that sense they are a pain, but when it comes to sims walking up and down multiple sims can use it as each step is like a separate set of stairs. With the fixed stairs the whole stair case is one mesh which is why they only take one sim up and one sim down at a time because only one sim can use most objects or one side of an object (chess table) at a time.
Spiral stairs are different somehow as one sim can follow another, I don't know why though.

Sims can also slide down spiral staircases. That does it for me

How? Are they playful sims? Or is it a thing that just happens on occasion?

I was going to say that Jo - Spirals are also objects stairs so it appears it would be possible to have the straight object stairs multi-usable. It is annoying that thing with the stairs.

A later EP broke that, but move objects makes it places so it isn't that bad.

Noa1500 they may be playful, I haven't really kept check, but some sims love to slide down banisters. One of my sim kids in my medieval hood always slides down the spiral stairs, but they will do it on straight ones too.

I really want to know how some houses have 3 tiles left empty from the top, because my game only allows a minimum of 4
Moveobjects on etc don't help.
How did Maxis do it?

If you think stairs are an annoyance in The Sims 2, they're a misery in The Sims 1. All stairs in the game could only handle one Sim at a time, while everyone else had to wait at the bottom or top of the stairs for that one Sim to get off. And if their path was blocked...

@kasparlaks
Modular stairs need 4 tiles; object stairs only need 3.

I wonder if it has something to do with the fact that straight object stairs can be used by one sim in each direction, whereas the spiral stairs can't. Or, in other words, if the stairs allow two sims on them at a time... and the straight ones are one each way and the spiral are two the same way.

ETA: And with modular stairs, you can also "turn" them, by adding one (or more) square of stage foundation at the bottom, and the last square of steps can go downwards from the stage. IIRC that leaves three open squares above the stairs, too? I could be wrong.

I know, but Family Farmhouse for example has a modular staircase with 3 empty tiles.

Perhaps some kind of workaround from the base game/prerelease which no longer works?

You can make smaller gaps if you break the stairs up with a stage.

Yes there is another house with only 3 tiles, this was pointed out in one of the decorating contests once many of us started knocking out an upstairs wall and then found it could not be put back. It wasn't the farmhouse either but a pre-made house already down in one of the base game hoods. Obviously the development team could do some things that we can't. No cheat will let you replace those stairs with only a 3 tiles gap, not move objects or CFE, nor any modular cc stairs. I tried it all but in the end had to take a point hit for demolishing the wall and moving it back one tile.

I prefer spiral stairs but had the problem of only one sim able to use them at a time. Maybe it was Marvine's or it was changed later on. More than one can now use them. In small houses they take up much less space and are stackable. I still see many houses built with spirals at different locations on each floor, stacking them saves floor space at level two and up if placed over the first level stairs. The objects stairs never get used in my game and modular ones are used if not against an outer wall as they can be seen as a dark image in the neighborhood view.

Playful Sims, active Sims and children. And there is a slide down command when you click on the stairs, although they normally slide down all by themselves.

@Duine They can be stacked? Learned something new today... I always wished I could stack them. How can I stack them?

@Panam103 I'm not sure if you need move objects on, but try it both ways. This diagram shows the direction each level should be, it's like a continuous circle per each level. Decide where you want the stairs to be convenient at each level. Place on the first floor, at second floor place directly on top of the first set of stairs. This way you only use four floor tiles per level instead of eight on upper levels.