You know, we actually tried that for a while (search for Turnpike System or Turnpike Trusts on wikipedia), and it was an unmitigated disaster. Because turnpike operators had what were effectively local monopolies, they collected absurdly high fees and often spent as little as possible on routine maintenance, resulting in high cost / low quality roads. This was a major impediment to free trade, as it drove shipping costs to prohibitively high levels. The socialization of roads that took place during the Victorian era, along with the growth of the railroad industry, helped usher in the period of great economic and industrial expansion that lead to the Gilded Age.