Long before it was fully paved, the road that became Route 66 from Chicago to Santa Monica, Calif., was designated as one of the nation’s original numbered highways 100 years ago. Crossing vast stretches of Native American land in places like Oklahoma, New Mexico, and Arizona, it eventually delivered a steady stream of mobile customers to enterprising Native merchants selling everything from trinkets to fine jewelry and textiles to frybread. The signature eye-popping billboards and kitschy neon signs that defined the route are mostly gone, but a few hold-out examples of 50s road-trip culture remain. And a number of new businesses are expecting to cash in with renewed interest in an old highway.