The first video, produced by Harry Miles, shows a trolley going down Market Street in San Francisco, CA just days before the devastating 1906 earthquake. Notice the letter carrier on the right with his satchel. He is waiting with a small group to board a streetcar. While mail trolleys carried mail to be sorted, regular trolleys often carried letter carriers from their routes back to the post office.
The second video (min 3:17) shows a wagon waiting to make an exchange with a trolley mail car on Pennsylvania Avenue in Washington, D.C. in 1903.
[sounds of street traffic]