I suggest Gerald D. Feldman's Army, Industry and Labor in Germany 1914-1918. Despite its age, 1966, I have not read a better book on the German War Economy.
Feldman covers some additional data points on the rails. He focus' on the coal shortage but also mentions the general over taxing of the railnet. One military crises after another, having to take over most movement of raw materials as barge system just stopped from hard freezes in winters of 1916/17 & 1917/18. Also talks a little bit about the maintenance issue and the fact that the Hindenburg program robbed more manpower from the railway repair units as people jumped jobs to higher paying factory work. So there was not enough manpower to do repairs. Plus the railway authorities didn't even tell the civilian government and military authorities there was a problem till after the crises started to hit in 1916.
One last thing Feldman talked about was that factories to make shells setup once the war started were almost all crowded into Berlin. So the factory owners could be closer to War Office. So what happened was steel was shipped to Berlin, turned into shells and then shipped back to the Ruhr, then filled with explosives and THEN shipped to the front. So shells had to cross Germany twice going to and from Berlin for no other reason than factory owners had direct access to War Minister in Berlin.
Michael
I finally managed to find my copy and in his chapter on the coal and transportation crises, Feldman tributes much of this to the Hindenburg program and inefficiencies in the transportation setup, which was exacerbated by the coal shortages, which in turn mostly goes back to the Hindenburg program.
Though your figures from "Race to the Front" indicate there were other issues from 1917 on, which partly have to do with the great strain that the Hindenburg program's implementation had on the rail net (shifting of nearly 1 million people around for building/manning factories, shifting building materials, supporting building programs, etc.), which probably would not have occurred without the plan going in to effect. Feldman and principle actors of the period (Groener for example) seems to support my position that without the Program German production would have gone up in all categories, the coal and transportation crises mitigated by the War Ministry through responsible step-by-step increases in production and responsible handling of shortages/industry inefficiencies, and nearly 1 million more men would have been available to the army over the OTL number.
Also the pressure for unrestricted submarine warfare would have been mitigated, as even Ludendorff's experts were telling him it was not worth it and the navy's numbers supporting unleashing the subs were bunk, but he did it anyway because of the crash in production. Also the pull back to the Hindenburg line, according to Feldman, was caused by the shortages in explosive production thanks to the failures of the Program and the manpower shortages to the army thanks to the combing out of workers for factories that were either not used or shut down shortly thereafter anyway due to lack of raw materials. Without the Program Feldman seems to suggest that the German army could have gone on the offensive after the failure of the French offensive at Chemin des Dames and been close to Amiens with the French unable to help the British.