Trying using private, available land for your comparison. Nobody has built a single story home up here for a long time. They crowd townhomes on top of each other all over the place. New single family dwellings are often built on lots that are not much home. I bought a 40 year old house so I could get 1/4 acre.
So, build further up. Houses in my town are on 2,500 square foot lots. Wouldn't it be a lot cheaper for the federal government to buy up your 1/4 of an acre and put ten townhomes on it than to spending hundreds of millions of dollars on a bridge?