Streetcars dominated transportation in D.C. during the first half of the 20th century, taking up most of the space on the roads Pierre L'Enfant envisioned in the master plan of the city. After the large increase in automobile traffic, streetcars were converted to buses, and the roads of D.C. grew more crowded than ever.
With the signing of the Federal Aid Highway Act of 1956, the Highway Trust Fund was formed to provide 90% of interstate highway road funding, with states providing the other 10%. This created a boom in the development of highways, with over 33,000 miles added across the country in the first ten years after the bill was signed. In Washington, D.C., plans for a highway system were drawn up to create two beltways, one outside the city and one downtown.
The idea for an Inner Loop with avenues and one-way streets was originally concieved in the 1940s, but with growing population and automobile ownership, the plan was expanded to freeways. In 1955, a report on the design of the inner loop highways was released by a private firm. This emphasized a combination of raised and lowered freeways to cut between neighborhoods. The digitized report can be found on this site.
