Sometimes when the state and federal governments have concurrent authority, the federal government can decide to regulate that area exclusively. In such a situation, according to the doctrine of , the state law is unconstitutional.

Federal Preemption.

Explanation:

The Constitution’s Supremacy Clause provides that federal law is “the supreme Law of the Land” notwithstanding any state law to the contrary. This language is the foundation for the doctrine of federal preemption, according to which federal law supersedes conflicting state laws.

In the law of the United States, federal preemption is the invalidation of a U.S. state law that conflicts with federal law.

Preemption is the rule of law that if the federal government through Congress has enacted legislation on a subject matter it shall be controlling over state laws and/or preclude the state from enacting laws on the same subject if Congress has specifically declared it has "occupied the field." Preemption can occur by Congress passing a law, preempting state or local law. If Congress has not clearly claimed preemption, a federal or state court may examine legislative history to determine the lawmakers' intent toward preemption.

Explanation:

answer; eliminate parking problems in cities, because a car took up only half as much space as a horse and buggy;