Whether the entire island of Manhattan can be enclosed by an eruv remains a controversial question. The issues are whether the eighteen bridges around the island that can transport in excess of 600,000 people to and fro are considered directly connected to the highways running through Manhattan, so as to render them mefulash and thereby make the island a reshut harabim. If they indeed do, then traffic transporting in excess of 600,000 people in one day through mefulash highways means the island cannot be enclosed by the unobtrusive device of tzurat hapetach, and the impractical device of gates capable of being closed at night would be required.
Many poskim, starting in 1949 with the Amshinover Rebbe, endorsed the enclosure of Manhattan by a tzurat hapetach eruv. Rabbi Moshe Feinstein, in a 1951 teshuvah concerning Manhattan addressed to Rabbi Tzvi Hirsch Eisenstadt and in a 1981 teshuvah concerning Brooklyn, questions the halachic basis of such an eruv. Rav Feinstein’s main concern is that the access to and from Manhattan of numbers of people far in access of 600,000, through bridges that connect to the highways, renders Manhattan a reshut harabim. Some poskim of great stature disagree, however.