You're welcome! Route 28 serves two major shopping centers, two Meijer stores, lots of big-box stores like Home Depot and Target, two public libraries, and more. It also has a mini station where it transfers to several different routes. It may be busier than you're looking for, though. Route 15 (East Leonard) might be a good possibility. It goes downtown, past medical centers, museums, restaurants, movie theater, and to a Meijer store (our area's largest brand of supermarket), but also passes a couple of complexes with housing for people with disabilities, where there are likely to be target customers that could be helped by what you're offering.
Are you sure route 17 is one of the busiest? As a bus rider, route 17 seems to be the one with the fewest riders. Also, because there is only one bus that serves the airport, it would be easier to get on the right bus than some other routes. Might I suggest Route 28 as a pilot? It's a long, crosstown route with quite a lot of riders, and lots of places to to make transfers. Or checking with the Association for the Blind and Visually Impaired to see where more people with visual impairments live in Grand Rapids?