I don't know St Petersburg. It may be that there is no public transport on that route, but that seems unlikely if it is in the city itself. If you've set your location as said by catymag, have you got all transit types enabled as Giomen suggested? Tools>Settings>Navigiation>Transit Types:

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If that's ok, try the route that i did before. It's much longer than yours but still involved quite some walking at the start and finish:

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