Contemporaneous newspaper articles were pretty good at documenting when abandoned streetcar tracks were covered over by asphalt, which was more often than not. Paving was cheaper and quicker than removal of track that was often embedded in concrete. Even today, historical track pokes up through the road surface all over Portland.
The first major repaving program began in 1936 immediately after the abandonment of a number of streetcar lines. Aided by WPA labor and federal funding, track was removed more often than with subsequent programs where funding was not as easy to obtain because of World War II or post-war austerity. In 1941–1942, it was proposed that abandoned track could be dug up and used for the war effort, but judging by how much still remains under the streets of Portland today, it would seem that little came of this plan.
See also: Historical Track Removal