Final answer:
Crossbuck signs are used on multilane roads to mark railroad tracks crossing the roadway and warn drivers of approaching trains.
Step-by-step explanation:
On multilane roads, railroad tracks crossing the roadway are marked by crossbuck signs. These signs consist of a white X-shaped crossbuck with the words 'RAILROAD CROSSING.' The purpose of the crossbuck sign is to warn drivers that they are approaching a railroad crossing and to remind them to look for trains. The crossbuck sign is considered an advance warning sign and helps ensure driver safety.