WASHINGTON — A speed restriction on Metro will slow the trip through the District for almost three weeks.

Metro announced on Thursday that the westbound track of the Orange, Silver and Blue lines (in the direction of Vienna, Wiehle-Reston East and Franconia, respectively) will be placed on a slow speed restriction between Metro Center and McPherson Square.

That restriction will last until Aug. 31.

Metro says the restriction is to allow workers to remove a restraining rail and repair a tight curve. It could result in delays of 15 to 20 minutes.

Eastbound trains, heading toward New Carrollton and Largo, will be unaffected.