69    Crossings.

Where tower lines cross over major railroads (See Rule 22.2-B), or major communication lines (see Rule 20.5-A1), or other tower lines of voltages exceeding 30,000, the towers supporting the crossing spans shall be designed to withstand with safety-factors of Section IV, the most severe conditions of temperature and loading therein specified, combined with the unbalanced pull which would be caused by any two conductors dead-ended or any two conductors broken in the span adjacent to the crossing.