I have found a book on anti-trust exemptions. There are three categories of exemption.
This initial survey is to find examples in law of antitrust exemptions that model the law needed to enable the public bus to carry freight carts.
There are several areas of law that have operated against public bus service changes. "Unfair competition" is one area and in the United States, much of the law is called antitrust law.
Anti-trust law has a long record of being a very mixed public benefit. See this Wikipedia entry:
Wikipedia Sherman Antitrust Act
Category 1: General exemptions from antitrust. There have been no new exemptions in this category in 50 years.
Category 2: Transactional or event specific exemptions from anti-trust law. Here is a link to a Google Books web page:
Federal statutory exemptions from antitrust law, American Bar Association Section of Antitrust Law, 2007, page 38
Category 3: Modifications of anti-trust law for the benefit of some class or activity.
Two anti-trust exemption models appear in the Category 2 listing on the URL above.
First, on page 42 is a description of the anti-trust exemption called "Collective agreements among motor carriers."
I don't consider this a model to be studied without regard to the poor outcome of the exemption. Frankly, my contact with motor carriers in the home furnishings transport business means this exemption is a license to charge huge amounts for moving service. The family goes along with the high charge due to the moving expense deduction in the Federal tax code. A side effect of the collective agreement is cheaper strategies like renting a 32 foot trailer and loading it yourself are not available.
Second on page 48 is the "Surface Transportation Act". This requires close reading.
Third on page 52, a Category 3 exemption is the "Local Government Antitrust Act". This law also requires close reading because it is a very confining statute. The exemption is counter balanced because the statute also allows local governments to be sued using anti-trust laws.