49 C.F.R. § 511.46
Within a reasonable time after the closing of the record and receipt of the transcript, all parties and participants may, simultaneously, file post-hearing briefs, including proposed findings of fact, conclusions of law and a proposed order, together with reasons therefore. The Presiding Officer shall establish a date certain for the filing of the briefs, which shall not exceed 45 days after the close of the record except in unusual circumstances. The briefs shall be in writing, shall be served upon all parties, and shall contain adequate references to the record and authorities relied on. Replies shall be filed within fifteen (15) days of the date for the filing of briefs unless otherwise established by the Presiding Officer. The parties and participants may waive either or both submissions.
49 C.F.R. § 511.46