A method for delivering and maintaining mandatory directives data from a central office server to an on-board system. Mandatory directives include the enforceable train control data required for a train operating on controlled track. The method enables the on-board system and the central server to exchange data in a vital manner, in part by checking for any inconsistency between i) the on-board system's data as previously transmitted and ii) the required data as represented by both a transmitted set of data identifiers and an associated error correction code.