CARLSBAD, N.M. (AP) — The primary elevators that take visitors below ground at Carlsbad Caverns National Park are being modernized as part of a project that began this week at the southern New Mexico tourist destination. The National Park Service announced the start of work Tuesday, saying it will include installing new motors and elevator cars as well as repairing and installing guide rails. Originally installed in 1955, the primary elevator system went out of service in November 2015 when a motor shaft unexpectedly sheared off. The work is expected to be done by the end of May 2018 at a cost of about $4.7 million. The park continues to provide visitors with access to the caverns via its secondary elevators and the trail that descends through the natural cave entrance.