Posted speed limit signs are examples of statutory law. A statutory law is any law that the legislature establishes as a statute, which means it is formally written and enacted.
Statutory laws are acts passed by legislature, and have two designations: private law and public law. Private laws relate to specific institutions or individuals, while public laws are written for the general public to abide. Most laws passed by Congress are considered public laws, such as speed limits, legal drinking age and laws about cellphone use in school zones. Most private laws are enacted to help citizens recover from injuries by government programs. An example of private laws includes deportation.