Complex sentence: The project was first proposed in 1854, but was postponed due to the challenges presented by the region's severe topography; work on the Nilgiri did not begin until 1891 and the route was not completed until 1908.
Split into simpler sentences: The project was first proposed in 1854, but was put off due to the severe topography of the area. Work on the Nilgiri did not being until 1891 and was not completed until 1908.