It seems to just double the track points. From the base game rulebook:
RRR Rulebook, p.19 wrote:
Important note for this railroad: when a player reaches space 7 of this railroad with his gray rail and a locomotive, the value of all scored spaces on his St.Petersburg railroad are doubled.
The spaces on this (Kiev) railroad are scored like those on the other two railroads. The special spaces of the Kiev railroad are spaces 1 through 4 and space 8. A player that reaches theses spaces with
his black rail and a locomotive will also score the points noted in the stars.
So, the extra points are not attached to the "scored spaces". The tracks are just the precondition.