lichvoid haGa’on shlit”a vechol chevrayo kadishat hodayn
The question concerning the difference between GG and yerusholayim is very very valid, especially as the BaDatz Eida hachareidis and haGaon r; Chayim wosner shlit”a clearly spoke out against the GG eiruv despite the eiruvin in their pwn towns.
1) R’ meir Rosner has made his feelings clear that one may not carry on most the main roads in yerushalayim, including recently the sheaf Chayim road. As such one is limited to the loacal eiruvin, I think many are makpid not to carry on Shmuel hanovi or Bar ilan etc.
2) Even the eida hachareidis eiruv excludes kvish one, kvish nine [except for the tunnel to ramat shlomo] etc… the other rads have police barriers in place on Shabbos, as such at least on Shabbos they are very different and possibly this effects their denim even when the barriers are not in place. The same applies to b’nei b’rak, there are barriers by the coca cola bridge on kahaneman and in other places.
3) as far as I heard R’ ehrentrau shlit”a said that even with a tzuras hapesach at Spaniards inn he agrees that it is not a rambam eiruv.
4) R’ Yosef Babad – belzer dayan of Stamford hiil has said that it is unfair to compare townhouses with front and backyards to e”y where people live in 50 or 70 sq mr with a large number of children, many windowless machsanim, and many do not use electricity on Shabbos. as such he has said that the leniencies in place in e”y cannot be used in London.
5) Rabbi Roberts says that r’ shimon eider told him that the a406 and a1 are undoubtedly reshuyois harabbim, and cannot be compared to Israeli roads. he has expressed himself extensively on the subject, and repeatedly said that there are questions of de’oiraysa involved.