This question was on my mind when, in the Meme region of Cameroon, I saw motorcycle passengers come to a full stop, dismount, carry the bags of vegetables they were transporting on their backs, and start pushing the vehicle to the side, over a field--to circumvent the huge pool of water interrupting the rural road in front of us. Soon, they were on their way again.
Meme is a remote region with almost four meters of rain per year. The state of its roads reflects the very limited investment they have seen in the last decade.
The motorcycle story from Meme shows that, even in extreme climatic conditions, the connectivity of roads is maintained. A road may be impassable for cars, but motorcycles find their way around. Therefore, most rural populations are somehow connected to markets, whereas connectivity is usually thought of as either 0 or 1.
This means that investments in roads could have a lower-than-expected impact on economic development since most households are already somehow connected.