If a sprinkler system is installed, then Exception 2 of Section 1007.3 does not require the clear width of 48 inches between the handrails.
Handrails can project into the required stairway width by 4.5 inches on each side. Therefore, the minimum 44-inch width can be measured to the wall if the handrail does not project more than 4.5 inches.
The 2009 IBC has requirements that make this a little clearer by stating that the projection can be at or below the handrail height; thus, a guardrail with a handrail directly on the top does not reduce the required width, and the required width can be measured to include the space 4.5 inches beyond the stair-side face of the handrail if no wall exists.