Building bridges (and roads)

Jonah and I built a road using cardboard blocks. He was pretty happy with it, but wanted to make it longer. I said "Go ahead and add some more blocks to the end." He came back a minute later and said "There aren't any blocks the right shape." He was right -- we had used all the blocks that fit together to make the road. There were other blocks around, but as he pointed out, they would leave a bump in the road.