a phrase describing an action that must be executed quickly and accurately in the face of circumstances that cannot be forestalled; generally used in extremis, as in “Our competitor is releasing next week so we have no choice but to launch the software and patch with live updates based on customer feedback, we’re going to have to lay tracks in front of a moving train; this approach risks spectacular failure if not impeccably managed, evoking the pileup of derailing train cars, but is necessary when there is insufficient time for a more deliberate approach