[Code of Federal Regulations] [Title 49, Volume 4] [Revised as of October 1, 2004] From the U.S. Government Printing Office via GPO Access [CITE: 49CFR234.231] [Page 529-530] TITLE 49--TRANSPORTATION CHAPTER II--FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION PART 234_GRADE CROSSING SIGNAL SYSTEM SAFETY--Table of Contents Subpart D_Maintenance, Inspection, and Testing Sec. 234.231 Fouling wires. Each set of fouling wires in a highway-rail grade crossing train detection [[Page 530]] circuit shall consist of at least two discrete conductors. Each conductor shall be of sufficient conductivity and shall be maintained in such condition to ensure proper operation of the train detection apparatus when the train detection circuit is shunted. Installation of a single duplex wire with single plug acting as fouling wires is prohibited. Existing installations having single duplex wires with a single plug for fouling wires may be continued in use until they require repair or replacement.