interlaced alternating stairway
Two alternating stairways threaded together.
This type is used sometimes in high-rise buildings as a means of concentrating maximum stairway access into a limited space. Its space efficiency is even greater than hairpin a stairway's because it does not require intermediate landings, and it allows better transportation of large objects because there are fewer turns. However it is generally practical only when there is a need for multiple stairs within a small space.