Map of US highway 54 and family, and US 400
US 54 is represented by the purple line beginning in El Paso TX. Its eastern terminus is currently near Pittsfield IL; the red line extending east of there to Chicago is the historic extent of US 54.
US 154 (historic) is the red line beginning in Dodge City KS. Its original terminus was in Bucklin; later it was rerouted to Mullinville.
US 400 is also shown on this map (the green line from near Joplin MO to Granada CO). Because its number is a major violation of US route numbering conventions, I included it on this map to demonstrate how the highway would fit into the US 54 family, if it were to be assigned a number US x54. (This is just one possibility that makes more sense than 400; I've also included the route on the maps for US 50 and US 66).