A cyclist riding near the curb ahead of you suddenly swings out toward the middle of the lane as they approach a set of streetcar tracks. Why?

Correct answer: D. To meet the rails at 90°, so the tires cannot drop into the groove

To cross the tracks at a right angle. Cyclists are normally expected to ride about a metre from the curb or parked cars, but the Handbook lists the situations in which "they can use any part of the lane if necessary for safety" — and one of them is to "cross railway or streetcar tracks at a 90° angle." A narrow tire that meets a rail at a shallow angle drops into the groove and the bike goes down, so the swing out is not carelessness but the only safe line. The same list covers avoiding puddles, ice, sand, debris, rutted pavement, potholes and sewer grates, and discouraging passing where the lane is too narrow to share safely. Expect the movement, leave room, and do not read it as an invitation to squeeze past.

Source: MTO Driver's Handbook: Sharing the road with cyclists — when a cyclist may use any part of the lane