On a recent Monday, I decided to stop and look for a while, in this case for one hour, at people walking past. I photographed the anonymous flow of Pittsburghers during the afternoon rush hour, from 4:32 to 5:35 p.m. near a bus stop on Penn Avenue in Downtown. I was on the opposite side of the street, so there was no interaction with the subjects. They didn't know they were being photographed. I accepted those that came by in that one hour. The yellow wall formed a blank background, so I could focus on their faces.

One can only try to guess who they are or what they do in this life. Some people isolate themselves with headsets and music. Others talk on the phone. Some talk to companions as they walk together. A construction worker has dirt on his face and equipment on his shoulder. A mother has her children in tow. Students wear backpacks.

Being a student of history, and especially photography history, I am aware of and inspired by Walker Evans in doing this series. Mr. Evans is well-known for his photography for the Farm Security Administration during the Great Depression. In 1946, while working for Fortune magazine, he published a series called "Labor Anonymous" in which he photographed workers in Detroit as they walked by him. He captured people unaware by pointing the camera up from waist level.

The facial expressions I captured on a Monday afternoon in Pittsburgh sometimes surprised me. It seems that people are lost in their thoughts when alone. Each photograph is a document of a single moment, for us to study today and decades from now.

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