Three Metro workers have been disciplined after letting a 10-car train run the length of the Red Line last month.

The incident happened on Dec. 2 when the extra-long train left Shady Grove around 2:13 p.m. It traveled the full line to Glenmont, said Metro spokesman Dan Stessel. That’s unusual as in the past, such extra-long trains have typically been caught and stopped after traveling just a few stations.