As one long fascinated with the railroads of our country, I long ago learned that the "hotbox" was the bane of the early brakemen and conductors, especially on freight trains. The wheel assemblies on both freight and passenger cars are called "trucks." Most have two axles, the ends of which rotate freely in ball bearing "journal boxes" which had to be oiled or greased regularly to prevent "hot boxes" which often led to fires that could be catastrophic. The invention of the Timken roller bearing nearly eliminated the problem and is in universal use even now. Your own car probably has a version on each wheel. It's no wonder that the early days of our railroads gave birth to any number of songs and stories about the dreaded "hotbox."