Key points: - The company building the railway says it will lift more than a million people out of poverty - Scientists warn the route cuts through vulnerable habitats and above thousands of subterranean caves - Local villages support the train as the project brings jobs and customers In the eyes of President Andres Manuel Lopez Obrador, a railway his government is building — known as the Tren Maya — will bring modern connectivity to areas for generations deprived of significant economic benefits.The railway "is splitting the jungle in half," says Ismael Lara, a guide who takes tourists to a cave that shelters millions of bats near the Calakmul Biosphere Reserve.Over almost a year, Reuters photographed construction at points along the full length of the planned rail track, documenting the evolution of the flagship project which Mr Lopez Obrador has pledged to finish by the end of 2023.If built badly, the railway risks breaking through the fragile ground, including into yet-to-be explored caves below, says Emiliano Monroy-Rios, a Mexican geochemist with Northwestern University who has extensively studied the area's caves and cenotes.Dozens of scientists disagree, writing in open letters that the assessments are riddled with problems, including outdated data, the omission of recently discovered caves and a lack of input from local hydrology experts."