Tomorrow, for the first time since 1991, a new Metro line will open. In a sense, the start of passenger service on the first phase of the Silver Line isn’t quite as momentous as the advent of the Green Line 23 years ago, since the former largely duplicates the Orange and Blue lines and the latter opened up impoverished and previously isolated sections of the city to the subway grid. But remember, when the Green Line opened, it initially had just three stations that hadn’t been served by Metro, compared to the five the Silver Line will bring.

Don’t quite have your Metro history straight? David Alpert at Greater Greater Washington has you covered. He created this interactive timeline of Metro’s growth over the years. Watch the system grow, from its birth in 1976 to the Silver Line’s opening tomorrow and eventual expansion:

Photo by Darrow Montgomery; interactive courtesy of Greater Greater Washington