I use a lot of Triz when I look at things.

http://en.wikipedia.org/wiki/TRIZ

Most problems that we encounter have been encountered before. The circumstances are never the same so neither are the answers. But, if done properly, it can accelerate the development process.

In WW2 some of the cities became so heavily damaged that the roads were clogged with debris and thus greatly hindered movement. In addition, Snipers were the IED of that age. To obtain a less obstructed route that protected them from surface threats, they used the sewars to move about. Rattenkeig. War of the rats.

Not highlighted in an episode, yet. But, I want people to keep alternative means of transportation in mind and I do not mean the a hybrid. In movies I have seen of LA, I think there are also cement canals that handle heavy rain run offs. These are open to the sky, but they are sunken and would suppress line of sight and scent down wind.