Canadian National Railroad Practice Exam

Speed restrictions are generally applied to the entire train or movement. The exception to that rule is signaled by a Head End Rule, abbreviated HER. When HER is identified, the restriction applies only to the head end of the train—the leading locomotive—rather than the whole train. The trailing cars aren’t bound by that particular restriction, so crews must handle the movement with awareness of which parts are restricted and which aren’t.

Other ways speeds can be communicated—sign boards, RTC directives, or dispatcher signals—still convey the applicable speed limits or authority, but they don’t serve as the specific indicator that the restriction is limited to the head end.