What's the difference between building a bridge to nowhere and building roads/bridges that lead to empty jobs?

So building roads and bridges isn't building a product that the rest of the world will buy right? So why don't we invest that money in research and development to make a product that others will want to buy for very long time? This would create jobs that will last and produce tax dollars to build the necessary roads, bridges, railways, waterways, etc. Not everyone that needs to work is physically fit to build roads. I say we give the top inventors in this country a grant of the $17 billion the car companies got and you'll see real American innovation at work. I'm sorry but we are throwing money at an industry that other countries do better and cheaper than we can. We need to accept that and move on to the next big thing.