In short, paving a road that doesn't need paving is a pissing away of the taxpayer's dollars. That money could more easily be useful if you just return it to the people. Why?
You'll get the same amount of production which will show up in the all-important GDP figures AND people will actually get a use out of it.
This is the biggest fallacy facing expert economist's today. They're concerned too much about hollow numbers and not about standards of living.
Now, a shinny new nickel to the person who can explain why this won't help the economy, but will improve numbers.