It is important to understand that strict adherence to the code formula for setting the back-to-back/row spacing does not create a comfortable sitting space. Typical row spacing used today is 36" and when used with a standard auditorium-style chair that spacing provides clear passage of 17" - 19" (depending on back pitch, model, accessories, etc.).
This 36" spacing should be considered the minimum in the design of public seating space. The addition of higher backs, thicker foam, writing tablets or cupholders should increase the spacing accordingly so access to the interior of the row is relatively easy—even when passing patrons that are already seated.