>>are subsidized by the government (very few toll roads exist in the US, it's mostly combination State and Federal funding which builds highways.)
Toll Roads is not the only User Fees applied to fund roads. Other Fees include but are not limited to Gas Taxes, Vehicle Excise Taxes, Registration Fees, License Fee's, Wheel Taxes, etc.
That is with out adding in other revenue's that should also be considered user fees but typically are not like Vehicle Sales Taxes, and Fines for traffic violations.
Americans pay a TON of money directly in fees for access to the road system above and beyond tolls
Further the Interstate system is considered to be a National Defense project, that citizens are allowed to use, kinda of like GPS.
>>The USPS might be able to turn a profit
"Run like a business" do not mean "turn a profit". Not all businesses are for-profit enterprises.
A better turn of phrase may be found in the axiom of "Government Programs are judged by their intentions, Private Enterprise is judged by their results"
"Run like a government" generally means a program is not judged by the results of the program, and any failing of the program is simply a matter of spending ever increasing amounts of money never critically looking at either the program itself or the assumptions of the programs
"Run like a business" means looking at the objectives, setting a goal to achieve the objective, taking action, then evaluating the results of the action. Looking for inefficiencies, bad objectives, false assumptions, etc etc etc.