Unfortunately I have no time to code this up but things that I would try to make it fast:

- Read with O_DIRECT (but compare it with the mmap approach). I know O_DIRECT gets much hate, but this could be one of the rare cases where it helps.

- Use a simple array with sentinel and linear search for the station names. This is dumb, but if the number of stations is small enough this could beat the hash. (In the back of my head I have a rule of thumb that linear search is faster for up to 1000 elements, but I'm not sure anymore where I got this from).