Not in 1942, at least in working condition. After the abortive Soviet offensive that captured Kharkov in the winter of 41-2, the supply heads for AGS were pushed back several hundred miles. The German Rail Authority was already struggling in the east to keep frontline units supplied by that time, and complete the repairs to the Soviet rail system. Germany had started the war in Russia short of both rolling stock and prime movers, and had found much of its German locomotives and carriages unsuitable for the eastern front. These problems were eventually solved, by modification to both the rolling stock and the trains, but such work was slow. The states of many bridges and rail lines in Russia were found to be extremely poor, and the captured equipment fell apart very raipdly.
All of these problems were eventaually solved, but it all took time, and time was something germany did not have. moreover the stockpiles of supplies needed to repair or replace sections of track, install water and coaling stations, develop marshalling yards and the like had been basically used up in the 1941 campaign. Replacement supplies of this kind were slow in being produced and brought to the front where needed. moreover the German State Railways were beginning to suffer the first of their acute manpower shortages. They attempted to remedy this by employing local labour, but this proved rather abortive and unsuccessful.
The result of all this was that the advances achieved under Fall blau were not matched by a repair and re-gauging effort much beyond the start lines. This is one reason why Stalingrad, and the advance of 1Pz and 17 Army into the Caucasus became logistic nightmares for the Germans. The rail lines that you are relying on were there, damaged and inoperable, and they basically remained as such until recaptured by the Russians in the winter of 42-3. After the capture of the oilfields in Maikop, the German Supply Ministry (I think it was them) undertook an investigation and found that the oil wells were so badly damaged, it would take an estimated 2-3 years to restore them back to production, and would have required the diversion of military supply arriving by rail into the TO to the tune of a reduction of military traffic by an estimated 50% (I will confirm that figure tonite). Since military supply traffic on ASGS never exceeded 70% of estimated requirements, that means that the whole AG would have needed to reduce its daily military supply expenditursres to about 35% of what it thought it actually required, in order to restore these lines and network to anything like operational condition, and restore the economic infrastructure to working order. In other words, whilst Germany remained locked in combat with the USSR in major operations, it was impossible to extend the working rail network much beyond what it already was.
By comparison, the effort put into uprading the Iranian and Persian rail networks is generally unknown, and really quite astonishing. India has a rolling stock reserve bigger than the whole of Germany at this time, and in 1942 something like 45%of Indian rolling stock was moved to Persia for supply operations to support the Russians. The Americans provided very significant levels of prime movers to haul this rolling stock. Vast numbers of railway workers were shipped out from the US to build up the persian rail network. It was an effort far bigger than the Germans were capable of in Southern Russia at that time. The fact that the transfer of the Indian rolling stock probably was a major cause of the 43 famine in bengal (where more than 2million people perished from starvation) is worth noting, but not really relevant to the issue. There is just no way that the germans, despite operating on interior lines could match the logistic effort mounted by the allies into persia in 42-3, neither could a few well placed bombs make much difference, or cause delay to the re-supply activities. The Persian route for Lend lease was far bigger than the murmansk run, and this was a massive effort in itself.