Park Free Downtown ad, Washington Post, 1/22/1961, page A11 (scan)

In response to the rise of suburban shopping centers which were paired with big parking lots offering free parking, traditional commercial districts such as Downtown DC organized coordinated parking programs so that people could shop downtown without having to pay for parking. This ad is one of the promotions used to promote the program locally.

If you look at late 1950 and early 1960s issue of Parking magazine, the trade magazine for the National Parking Association, there are many articles/case studies of these types of programs, how they are set up and function, etc.

At some point, these types of programs disintegrated. I don't know when the program stopped in DC.

Ironically, we don't have an integrated parking system in DC today, especially downtown, and we don't have a wayfinding system of signage to direct people to parking options either. This is true in other parts of the city, such as Capitol Hill (for Eastern Market) where such a system is also necessary.