Updated at 6:46 a.m.

Metro said normal service is back on its three rail lines -- Blue, Orange and Silver -- after Monday’s crash in which two trains collided.

Original post at 6:00 a.m.

Riders on Metro’s Blue, Orange and Silver lines should expect delays Tuesday morning until 6:30 a.m., the transit agency said on Twitter.

The delays on the lines come a day after two trains collided early Monday morning, causing nightmare commutes for passengers on those same three lines.

An initial finding of the investigation showed one of the trains was traveling 11 mph when it hit a stationary train outside the Farragut West stop. Investigators are trying to figure out the primary cause of the crash.

No passengers were on the trains, which were returning to their rail yards. Two train operators were treated and released at area hospitals, officials said.

Officials had said that both trains involved in the crash were left on the track all day Monday because investigators needed to collect evidence, and because Metro did want to cause more disruptions by moving them while the system was running.

Getting the trains off the track required heavy utility prime movers, which are like a tug boat or tow truck, and it is a process that typically takes several hours because they move at slow speeds. The trains involved in the crash were 3000-series and they are “coupled,” so they have to be moved in pairs.

In an email, Metro spokesman Dan Stessel said that “normal operations resumed around 6:30 a.m. following successful test train runs.” He said Metro’s “Rush Hour Promise” is “back in effect on all lines this morning.” Under the program, Metro will issue an automatic credit for riders who are delayed more than 10 minutes.