Who decides when you're too old to drive?

Americans are keeping their driver’s licenses longer than ever and driving well into their old age. But how long is too long? And who decides when to take away the keys? NPR’s transportation correspondent, Joel Rose, has been looking into those questions and found that there is no single national standard when it comes to older adults and driving. And the laws vary greatly from state to state. Often, the decision on whether it is time to take away the keys is left to family members. And that can be difficult when the driver resists.