I'm not sure I agree with Certainly. I think it literally means 'down the road' as in 'not far away'. The book is about a 12 year old girl who finds it very difficult to make and keep friends, and the sentence "James has got Will Maycomb down the road, who is full of fun and mischief, and Lucille’s friend Ivadee is a year younger but seems just the same as Lucille, wanting to play house and schoolteacher all the day long." seems to indicate that other people make and have friends, whereas she does not.

Down the road, here, means 'along the road'/'nearby'. James has got Will living somewhere close. So I agree with Alex Kavanagh. 'Down the road' can, indeed, be used to refer to the future, as Certainly says. Example: Somewhere/sometime down the road I'll have to start working harder. But not yet! (One day I will need to do more work, but not now!) Going back to 'down' the road' - this could easily be 'up' the road - and it does not imply up or down in terms of hills/vertical change. It means 'along' the road. However, it can mean up/down/vertical change if the context suggests it.

"down the road" here means "in the future" The road is a metaphoric road describing the "path of life" Hope this helps :)