During Tier One, external working groups were formed. These working groups included the Corridor Planning Group (CPG) , which consists of Mayors or other representatives of the 27 communities as well as Cook and DuPage Counties. The CPG provided input and consensus on every major project issue. Three project Task Forces (Environmental, Transportation, and Land Use) were also established in Tier One. The task forces focused on technical project issues and provided a means for obtaining structured advisory input from a diverse set of stakeholders.