Although I can not much additional information on this library inspired week, it is a smaller alternative to the more traditional bookmobiles.
The week appears to be sponsored by https://www.facebook.com/abosoutreach/about/
From the Pima County (AZ) Public Library Book Bikes History
They may roll into town astride the Bookbike, Books on Bikes, the Bibliocycle, the BookCycle, or the Library on Wheels. They hail from such far-flung lands as Omaha, Tucson, Boulder, Los Angeles, Boston, and beyond. Neither snow nor rain nor heat nor threat of overdue fines stays these dedicated librarians from the enthusiastic completion of their civic appearances. They roam the neighborhood on customized bikes, trikes, tandems and trailers, heavy-laden with books but buoyant with good cheer. They are the biking librarians and their trusty book bike steeds, and they are coming soon to a community event near you.
Book bikes are the latest earth-friendly, human-powered mobile library outposts. They have been rolling through the streets of America since 2008 and are rapidly growing in number and popularity. Among the ever-expanding book bike fleet are those of the public libraries in Berkeley, Boston, Boulder, Cleveland Heights, Denver, Evanston, IL, Longmont, CO, Los Angeles, Maricopa County, AZ, Oakland, CA, Omaha, Pima County, AZ, and Seattle. Coming soon are library book bikes for San Francisco, Montclair, NJ, Rochester, MN, and Austin, TX.