Until 20 yrs ago, no studies were performed to measure this. Refinements have come in trying to assess risk based on type of epilepsy, past history of control, type of vehicle being driven. Unfortunately, this has produced marginal results. Scientific evidence is usually ignored in favor of strong political voices. Fortunately, the lobbying effort by physicians and patients has produced a gradual reduction in the period needed to be seizure free, and the exceptions for driving have been liberalized.
Many states have no seizure free interval defined and leave it discretionary.
Some states require periodical medical re-evaluation. The ability to appeal the decision of the drivers licensing division is sanctioned in some states with an appeals process spelled out through the Department of Motor Vehicles. Others are at the mercy of the courts and the judicial system. A bullet has been placed by those relevant to Neurologists. An arrow identifies subjects relevant to seizures and altered consciousness.