At some multi-lane crossings, the vehicle stop line is set noticeably farther back from the crosswalk than usual. What real safety problem is this "advanced stop bar" specifically designed to prevent?

Correct answer: B. A stopped vehicle blocking a pedestrian's view of a second vehicle, in another lane, that hasn't stopped

If the stop line sits right at the crosswalk, a vehicle stopped in the near lane can block a crossing pedestrian's view of a second vehicle in an adjacent lane that hasn't stopped — the pedestrian steps out assuming it's clear and doesn't see the second car coming. Setting the stop bar farther back opens up the pedestrian's sightline to that second lane, so they can actually see whether the second vehicle is stopping before they step out.

Source: MTO Driver's Handbook: Book 15, Section 6.2.4.2, Advanced Stop Bar