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I played tourist on Google street view. The large green road signs on highway 90 say "Iddan" with two "d"s before the turn-off in both directions. The white signs at the intersection pointing to the place also have "Iddan" in both directions. These are ordinary road signs. The Central Bureau of Statistics also uses IDDAN, see for example this and many other documents at CBS. I don't see any case for IDAN. Zerotalk14:11, 28 January 2013 (UTC)[reply]
Which isn't really an answer, since the issue is one of spelling not of name. But I don't feel like arguing. I've added the alternative spelling so that searches find it, and created redirects. Zerotalk13:57, 2 February 2013 (UTC)[reply]