State laws vary widely. Many states do not impose a legal duty to render aid, unless you are involved or caused the incident, or owe some sort of pre-existing or custodial duty to the victim, such as a parent, Scoutmaster, employer, etc. On-duty emergency workers obviously have a legal duty to respond, but off-duty emergency or medical personnel almost never do (contrary to myth). Oklahoma apparently imposes a legal duty, which I'm guessing may be an incident to issuance of a driver's license. You can also create a duty by beginning or appearing to render aid, since this may lead others to assume their assistance is not needed.

State "Good Samaritan" also vary widely in their scope of application and degree of immunity conferred.