Most stairs (at least here in the US) have an overhang or 'nosing' where the edge of the stair protrudes over the riser:
I've heard different reasons for why the nosing exists, but I've not been able to find a definitive source. Reasons I've heard are:
- It provides more space for feet (I'm not sure this is actually true, since it comes at the cost of potentially tripping on the overhang)
- It makes the stair more visible
- It somehow improves safety
- It creates clearance for toes and heels biomechanically
Can anyone show or point to a source which definitively shows why having the overhang is better than not having it?