I have a 6' length near the stairwell that's 20" wide, plenty of room for me (38" waist). This plan shows it as being a little over 24" but I just measured it.
It also depends on how high your layout is. I had a garage layout that had a spot that was only 15" wide, but the height put that 15" just above my waist. I could turn sideways and get thru but if had been any closer to my chest height it would have been a tight fit.
I run trains by myself, so I made the width on that. The grandkids are still small and pose no problems.