I had this happen today. There was a forest with a road in an adjacent spot. They will go for the 25 forest over the 15 forest even if it is further away. when i built my roads it picked the close forests.
I saw a screenshot of a setup like this on the official forums in which the citizen resource selection algorithm was failing to maximize productivity in the way you'd expect it to, so possibly this won't be quite as efficient as you expect.