Metro is making one of the biggest service changes in its history on Monday, all by moving around a few trains in what the agency is calling Rush Plus.

Some Blue Line trains will run on the Yellow Line during rush periods, which will cause a cascade of changes, including some Orange Line trains running on Blue Line tracks to Largo instead of New Carrollton. Some Yellow Line trains will run between Huntington and Greenbelt or Greenbelt to Franconia-Springfield.

Confused? Riders will need to start looking at where the train is headed, not just what color train is pulling into the station, as trains will run along different legs.

The service change will be only from 6:30 to 9 a.m. and 3:30 to 6 p.m. on weekdays, so riders outside those times won't be affected. The Red Line also isn't affected.

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Metro says the change is to make way for the Silver Line, now under construction. But the agency also says it will benefit some riders, giving more rush service to alleviate crowding. But about 6 percent of riders will see longer waits of 12 minutes on parts of the Blue Line even though they are paying peak fares.