By that logic: How can you actually increase utility for trains if you don't build a train? If public transportation is eschewed in favor of more roadways, then unsurprisingly the utility of the roads increases.

But, many studies have shown that building more roads does not reduce congestion. Congestion is not function of roadway space-- other factors like accidents, merging, exiting, peak travel capacity, etc greatly impact congestion. Building another lane on a highway doesn't solve the problem.