Coining the term “dual track” Desireé Sy‘s Adapting Usability Investigations for Agile User-centered Design(pdf) (2007) might be one of the first examples drawing out and labeling a process knows as dual track Scrum and stating, Although the dual tracks depicted (…) seem separate, in reality, interaction designers need to communicate every day with developers. This is not only to ensure that designs are being implemented correctly, but also so that we have a thorough understanding of technical constraints that affect design decisions