[Code of Federal Regulations] [Title 49, Volume 4] [Revised as of October 1, 2005] From the U.S. Government Printing Office via GPO Access [CITE: 49CFR236.5] [Page 589] TITLE 49--TRANSPORTATION CHAPTER II--FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION PART 236_RULES, STANDARDS, AND INSTRUCTIONS GOVERNING THE INSTALLATION, INSPECTION, MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCES--Table of Contents Subpart A_Rules and Instructions: All Systems Sec. 236.5 Design of control circuits on closed circuit principle. All control circuits the functioning of which affects safety of train operation shall be designed on the closed circuit principle, except circuits for roadway equipment of intermittent automatic train stop system.