I found a Guardian article [1] which quotes one of the people involved:

  "We started to think about how it would work with different typefaces, then started mood boards with different fonts and pictures – especially of old Swedish signs we'd seen from the 1940s and 50s," said Jesper Robinell, Söderhavet’s head of design.

[1] https://www.theguardian.com/world/2014/nov/14/sweden-sans-de...

I was originally thinking of the old Stockholm subway signage typeface. But it does not look similar

https://en.m.wikipedia.org/wiki/Esseltub

https://fontsgeek.com/fonts/Esseltub-Regular