The DOT may be on the verge of disclosing that the problem is operator error.

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Independent travellers can also contact a tour operator solely to purchase tickets, or reserve tickets through one of the many hotels that dot the rural Sacred Valley between the city of Cusco and the town of Aguas Calientes, the gateway town to Machu Picchu.

BBC: Securing tickets for Machu Picchu

The DOT crew in Dublin, roughly 10 miles from the crash scene, was called within a minute of the 911 operator's call and had loaded the caution signs into a truck and was en route when the Laurens County sheriff called the agency to report the crash, Goldberg said.

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