625 ILCS 33/20
Owners may submit voluntary programs as described in Section 15 to the Department for approval. The Department, after consultation with the Agency, shall determine the appropriate emission reduction credit to be awarded to owners who carry out their programs and to be used by the owners of stationary sources to satisfy the post-1996 emission reduction requirements under the Clean Air Act Amendments of 1990. Emission reduction credits shall not be awarded to owners for programs that are required under the Clean Air Act or the Environmental Protection Act or that are substantially the same as an owner's employees' existing level of use of employee commute options programs. The Department shall adjust credits to avoid duplicating the credits the State takes for similar transportation demand management practices under the applicable State Implementation Plan. Credits may be revoked for failure to achieve the reductions called for in the owner's voluntary program.
625 ILCS 33/20