It really depends on where responsibility begins and ends. It might make a lot more sense, financially, for the government to manage maintenance using supplies and equipments purchased from private companies, with the people working on the roads being government employees instead of employees of the contractors. However, for specific jobs - say building a new bridge, etc. - it might make sense to have that be a complete private contract, and then, after it's built, maintenance becomes the government responsibility.
In general however, there's too much opportunity for corruption if contracts are just blindly given to private interests by politicians. Iraq and Afghanistan reconstruction contracts were a good example of how bad that can get.
