Following directions that mention a highway number you cannot find, you pass a route marker with a small tab beneath it reading FORMERLY and the number you were looking for. What has happened?

Correct answer: D. The route has been renumbered — the tab shows the old number for at least two years after the change

The route has been renumbered, and the tab exists to bridge the gap. Book 8 says the "FORMERLY" tab "indicates the previous route number of a provincial route or other numbered route for which a new route number (provincial or other) has been assigned", and that it "shall be displayed for a minimum of two years following renumbering." So the road you are on is the road you wanted; only its number has changed. The two-year minimum is the useful part to carry: for a while after a renumbering, old maps, old directions and old memories will still work if you watch for the tab, and after that the old number disappears from the roadside entirely. Related tabs mark the ends of a route — a BEGINS tab under a route marker shows where a numbered route starts, and an ENDS tab shows where it finishes.

Source: MTO Driver's Handbook: Ontario Traffic Manual, Book 8 — Guide and Information Signs, Volume 1 (May 2010), Section 4.4 — Marker Tabs, "FORMERLY" Tab