The route runs for nearly 20 miles and comprises 131 stops, from upper St Johns to downtown Milwaukie.
Their pictures depict the wide range of communities spread along the way as well as capturing something of the gentrification in parts of the town.
Here is a selection of images from the project.
Bus 75: Hidden Portland was supported by a grant from the Regional Arts & Culture Council, a local arts organisation in Portland.
Photographer Geoffrey Hiller and writer Tom Vandel have spent the past year travelling on the number 75 bus in Portland, Oregon, stopping off along the way to explore and capture parts of the town usually only glimpsed thorough the window.