sentences:  The NER opened the Tees Valley Railway to in 1868.Doubling of the line to Tebay, except for Belah and Kirkby Stephen and Kirkby Stephen and Sandy Bank had been approved by 1875.The section between Belah to Kirkby Stephen was approved in 1889, and this involved the doubling of the Aitygill, Merrygill and Podgill viaducts.