The contractors have an incentive to underbid their competitors and possibly build a road of poor quality in order to keep costs low. You get a warranty with your new car. That's part of the reason you may have decided to spend a bit more and buy a car from a dealer as opposed to buying one second-hand. You want the warranty in case it breaks after you buy it. We can do the same thing with roads in Colorado.
Warranties typically indicate that a product is of higher quality.
The new Lexus comes with a warranty because Lexus is willing to guarantee the quality of the vehicle. In a similar fashion, a contractor who offers a warranty with his company's road indicates that the road is of higher quality. Instead of simply choosing the lowest bidder, governments should require a warranty on the road they buy. This would give the company incentive to build a quality road in the first place. After all, they don't want to spend money on materials and employees every summer to fill up numerous potholes and cracks.