Is the train from Interlaken to Lauterbrunnen covered by the Swiss Pass......How can I find out if a particular route is covered?
Yes, it is covered. There are some details about the coverage here on Rick Steves' website in the "Railpasses" section up above. Click here for a direct link.
Not only does the Swiss Pass cover the train from Interlaken to Lauterbrunnen, but the 100% coverage goes BEYOND Lauterbrunnen all the way to:
1)Stechelberg at the end of the valley
2)Wengen up from the valley floor
3)Muerren up from the valley floor opposite side
In addition you get substantial discounts if you go higher up in the Alps beyond Wengen and Muerren.
Thanks so much!