If you google ambulance trains national railway museum you should end up with a link listing a large number of books and articles on the subject
The list of books mentioned includes
o Anonymous “Diary of a Nursing Sister on the Western Front (Edinburgh London : William Blackwood and Sons, 1915)
o Bennett, Ernest Nathaniel, Sir “With Methuen's column on an ambulance train” Dodo Press, 2007
o Dunn, John Welldale Digital (DVD) recording of the World War One tapes of John Welldale Dunn containing information re his ambulance
train travel
o Fairman, J.R. “Netley Hospital and its railways” Southampton :Kingfisher Railway, 1984
o Friends Ambulance Unit “A train errant : being the experiences of a voluntary unit in France, and an anthology from their magazine” Hertford, Simson, 1919 (rare book)
o Gittins, Sandra “The Great Western Railway in the First World War” Stroud: History Press, 2010
o Gould, David, 1946- “The South-Eastern & Chatham Railway in the 1914-18 War” Towbridge: Oakwood Press, 1981
o Great Britain War Office “Railway manual (war) 1911 (reprinted with amendments, 1914)” Uckfield: Naval & Military Press I association with the Imperial War Museum
o Great Central Railway Company “63 ambulance train constructed for the United States Army Medical Department at the Great Central Railway Company's carriage works” Westminster : Knapp, Drewett, 1918
o Haller, John S., 1940- “Battlefield medicine: a history of the military ambulance from the Napoleonic Wars through World War I” Carbondale: Southern Illinois University Press, 2011
o Hamilton, J.A.B. (James Alan Bousfield), 1899-1971 “Britain’s railways in World War I” London: George Allen and Unwin, 1967
o Harris, Michael "Great Western Coaches 1890-1954" Nairn : David St John Thomas, 1993
o Holmes, Richard1946-2011,”Tommy: the British Soldier on the Western Front 1914-1918 London : HarperCollins, 2004
o Jenkinson, David "LNWR Carriages: a Concise History", york, Pendragon, 1995
o Lacy, R.E. (Raph Edwin) & Dow, George "Midland Railway Carriages" [Upper Bucklebury] : Wild Swan 1984-1986
o Langham Rob “The North Eastern Railway in the First World War” Fonthill Media
o Mayhew, Emily “Wounded: From Battlefield to Blighty, 1914-1918” London: The Bodley Head, 2013
o Millard, Philip A “LNWR Great War ambulance trains” Potters Bar :London & North Western Railway Society, 1993
o Moore, George Abraham “The birth and early days of our ambulance trains in France, August 1914” London : John Bale, Sons & Danielsson, 1992
o North Eastern Railway Company (Great Britain) “North Eastern Railway ambulance train” York : North Eastern Railway, 1917
o Plumridge, John H “hospital Ships and Ambulance Trains” London
eeley, 1975
o Pratt, Edwin A. “British railways and the Great War : organisation,efforts, difficulties and achievements” London : Selwyn and Blount, 1921
o Railway News “Records of railway interests in the War” London :Railway news 1915-1917
o Wolmar, Christian. “Engines of War” London: Atlantic, 2010