Updated with additional information in May 2018.
First, a sidetrack:
But is this in Arunachal Pradesh? The top script is in Bengali.
It is indeed adjacent to Silchar, in a part of Assam where Bengali and not Assamese is the official language. This picture was taken in metre gauge time. The large number of concrete sleepers strewn around indicates that broad gauge is on its way, and it has already been converted. This is the first station to the west of Silchar, on a BG line which now sees trains from Kolkata and Delhi. It is also the junction for the branch to Jiribam, presently one of the two stations in Manipur:
A limited passenger service served this station in metre gauge days, and broad gauge services are expected to start soon.
The line mentioned here is from Harmuti in Assam (on the Rangiya-Lakhimpur section) to Naharlagun (near the capital Itanagar) with an intermediate station at Gumto (which is also in AP). You can trace the route here (by expanding the map if needed). Note that the line to Naharlagun makes a U-turn from the main line at Harmuti.
The three stations:
And a quick look at the trains which serve Naharlagun today:
It includes a daily express from Guwahati and a (sort of) Rajdhani from New Delhi, which does not seem to have catering facilities. Also the average Indian citizen will not be allowed into the state without an inner-line permit or whatever it is called nowadays. More about this at the end.
Here is the timetable of the train from Guwahati to Naharlagun:
But what is forgotten is that there was a metre-gauge connection to Bhalukpong in the western corner of AP which was opened in the 1980s. In 1994 the timetable listed one pair of passenger trains between Rangapara North and Bhalukpong. The junction was at Balipara. They seem to have stopped running around 2000. More recently the line was converted to broad gauge.
The wayside stations are all in Assam except Bhalukpong station which appears to lie just inside the Arunachal border. Most of Bhalukpong town is in AP. You can see the map here and trace the path from Tezpur:
Also see the timetable of the present pair of trains, which run from Dekargaon which is now the station for Tezpur. The original station at Tezpur may have been abandoned as there was not enough space for a BG terminus there.
Passenger services on this line must have started in the last couple of years, but without the publicity that accompanied the line to Naharlagun which served the state capital. This line connects a town which may not be that important in AP.
These are some of the stations on this route:
And finally Bhalukpong in metre gauge days and the present. Note that the sign has English and Hindi, but not Assamese. This appears to mean that it is located in Arunachal and not Assam.
So you have now seen the full extent of the railway system in Arunachal Pradesh. Perhaps one day the rails will reach the borders of Tibet and Myanmar.
Footnote 1: Anyone from the rest of India wishing to enter Arunachal Pradesh needs a permit. This is apparently available online as well as from various offices of the AP government in Delhi, Kolkata and several cities in the Northeast.
It is not clear where the checking of the permit is done. Logically it should be at Harmuti (which is somewhat larger than Gumto, the first station in AP).
Footnote 2: see this map extract:
It can be seen that the Rangiya-Murkong Selek railway line briefly enters AP between the small stations of Dimow and Dipa. This stretch may be around 500 metres long, and presumably the AP authorities do not bother about “outsiders” passing through their state this way.