What company built a railway line that runs along the boundary between Hertfordshire and Essex for much of its length?
Northern and Eastern Railway: The Northern & Eastern Railway (N&ER) was the British railway company that built what is now the West Anglia Main Line, one of the two main lines of the Great Eastern Railway, the other being the Liverpool Street -to-Norwich line built by the Eastern Counties and Eastern Union Railways. West Anglia Main Line:  The line runs along the boundary between Hertfordshire and Essex for much of its length.
The Northern & Eastern Railway