While it's true that I often ride the bus and often ride my bicycle, I do not often ride my bicycle onto a bus. This means that I forget how it's done and have to refresh my memory. Fortunately, Arlington Transit uses the same bike rack design as we do here in Metro King County, so I can refer to their detailed pictures instead of our diagrams which leave a bit to be desired.
It's not that hard, really. There are instructions on the rack itself for most of the steps. You squeeze the handle where it says "pull here", lower the rack, place the front tire where it says "front tire", the back tire where it says "back tire", and put the support arm into place.
Two details are omitted from the instruction on the rack: First, if you're the first bicycle on the rack, use the slot furthest away from the bus. And second, how do you use that support arm?
I'm always baffled by the support arm. It won't fit over the tire! Oh, wait, because it's on a spring. You have to pull outwards in order extend the clamp. Then it will fit over your tire, and then you let it retract and hold the tire in place.
Metro has other tips on how to prepare your bicycle and the protocol to follow with the bus driver. One bus driver mentioned that the rack was designed by "some guy in Bellevue, or maybe Kirkland". Following up on this information led me to bike rack trivia: The racks are manufactured by Sportworks in the nearby town of Woodinville. Here's the Sportworks version of the story.
(And another Metro Transit tip: If you want a series of options clustered around a particular time, you can use the commuter trip planner, handy if you don't know exactly what time you will be returning. There's also the point to point schedule maker if you want a custom bus schedule between two stops. And no discussion of Metro Transit planning tools is complete without a plug for Bus Monster.)