I agree that there appears to be tracks on both bridges crossing the Bug, but why would both be the same gauge, when a branch would do? It seems that if there was a need for two bridges crossing the river, they would be different gauges to accommodate different types of traffic, such as industrial railways which were often narrow gauge.
I'm still not sure where the alleged post-war photo with parallel tracks at post #17 was taken?
This photo was taken circa 1962, which would explain why it does not show up in aerial photographs:
I do not think this was the Treblinka spur due to the fact it is not visible in 1944 aerial photographs. In the Fall 1944 photograph there is a clear path where the Poniatowo "road" turned into the Treblinka spur, which is another reason I believe the spur travelled that route:
That image to me looks like there is a railway coming from Poniatowo which turns into the Treblinka camps.
This photo was taken in 1945:
This photo does not seem to show the spur branching from the main line after the road intersection with Poniatowo. The railway seems to me to be turning from
Poniatowo in accordance with the path visible in the Fall 1944 photograph.
A later photograph of the Treblinka spur rails embedded in the road also seem to suggest that the spur was a narrow gauge railway, this one was taken in 1962: