Brilliant! Thank you Bob G! And yes, you are correct Sarushka, it is the building you identified on Akademicheski. The building still stands albeit in a poor state of repair and, sadly from the point of view of photographs, has a bright blue 8 foot high metal fence all of the way around. There is a typical tent roof to the entrance hall with a frescoed dome inside and ornate doorways and windows. A friend found for me an article in the www.tsarselo.ru
website which gives a lot more information and a map. This map shows the line continuing further than the dead end shown on the 1901 map, looping around on the Petersburg side of the Egyptian Gates and joining the town line into Vitebskiy Vokzal. There is no date on this map, which is hand drawn, and as the article amounts to a dozen or so pages of technical Russian I must await my next trip to Petersburg in August to get my friend to read it to me and find out more. The line as shown on the 1901 map joined the Gatchina line at Alexandrovskiy Vokzal to the south and presumably ran north into Varsharvskiy.
The hand drawn map shows two bridges over the Kuzmenka, one on the south spur, the other to the north. On Tuesday evening I explored in the company of two 'guides', members of the English Club from the adjacent Agricultural University. It is not a particularly exciting expedition unless you have good company and an appropriate Russian picnic on a pleasant evening! Only two pillars remain standing in the water of the bridge to the north. The bridge to the south, very close to Alexandrovskiy Vokzal, is intact. It is very plain with a little decoration at the top of the arch. There is still track over this bridge which runs into a nearby industrial site but it does not show signs of recent use.. Considering the fighting which took place in this area it is remarkable it has survived.... unless of course it has been rebuilt. I will know more when I have read the article. I will post more in late August if anyone is interested. Thank you all for your replies.