Red, Green and Orange line service affected Halloween revelers, Marine Corps marathoners, horse show fans and all-around city adventurers should take note: This weekend will be challenging for Metrorail riders.

The transit agency plans to squeeze all service on the Red Line to a single track through downtown D.C., and do the same on the eastern end of the Orange Line. It also will close four stations on the Green Line, shutting off rail service between the heart of the city and anyone who lives east of the Anacostia River.