When a road crosses more than one set of railroad tracks, what indicates the number of tracks to the driver, and what must the driver confirm before crossing?

AAMVA CDL Manual, Section 10.4.2 (Cross-buck Signs / Flashing Red Light Signals), p. 10-8; 49 CFR Part 380, Appendix D, Unit D1.6 (Railroad-Highway Grade Crossings)

A driver who clears one track but not a second, parallel track has not actually cleared the crossing. This rule exists because multi-track crossings are a well-documented cause of buses getting struck by a second train on an adjacent track.