While Friday is an anniversary of sorts, the Metrorail system didn't start running until March 27, 1976. That's when more than 51,000 people rode free over the 4.2 miles of track.
Two days later, 19,913 people paid to ride. Back then the rail system was open from 6 a.m. to 8 p.m. weekdays and was closed on weekends.
So what was it like to ride the rails that first week? Check out the video to see for yourself.
And if you want to see a good timeline of Metro's history, click here.