Amtrak has been ordered to retrain rail workers on basic safety rules days after a train going 106 miles per hour struck and killed two Amtrak employees working on the same track.

The mandate from the Federal Railroad Administration suggests the veteran Amtrak workers may not have known the track was being reopened to train traffic.

The directive, in bold print, orders Amtrak to reinforce the rule that a track will not be reopened until all workers have either left the area or been warned about an approaching train.

The engineer on the southbound Palmetto train Sunday had only five seconds to brake before crashing into a backhoe occupying the same track in Chester, about 15 miles south of Philadelphia. Backhoe operator Joseph Carter Jr., 61, of Wilmington, Delaware, and supervisor Peter Adamovich, 59, of Lincoln University, Pennsylvania, were killed.

About 30 of the more than 300 passengers aboard were injured, most with scrapes and bruises.

The National Transportation Safety Board, the lead agency investigating the crash, expects to issue preliminary findings within 10 days.

However, the directive issued Wednesday suggests the collision must have followed a breakdown in communication, possibly during a shift change. The crash occurred just before 8 a.m.

"FRA rules always require that a notification be made to the workers before there are any changes to their job briefing and an authority (protection) is given up," the agency directive said.

Amtrak Chairman Joe Boardman promised to comply with the order to remind workers of "the seriousness of following our rules to prevent accidents, injuries and deaths."

"We will begin the safety stand down immediately with all active crews," Boardman said in a statement Thursday.

With the deaths on Sunday, that makes three track workers who have been killed on the job on Amtrak's Northeast Corridor since March 1, according to their union.