There is no violation of the the Establishment Clause of the Constitution in permitting an eruv to be placed in the public "right of way". This is an accommodation under the law, not an endorsement of religion.  The items being accommodated are virtually identical and indistinguishable from items found on ordinary utility poles.
The Church / State argument has also been litigated at length.  In discussing this issue in the Tenafly action, the US Court of Appeals for the Third Circuit said they found the "the Borough's claim that it can remove the eruv because of its religious nature" to be "unpersuasive".
In that case, the Borough of Tenafly argued that the decision to remove the eruv was "justified by its "compelling" interest in avoiding "an Establishment Clause controversy."
The Court declared:
"Contrary to the Borough's position, however, a government interest in imposing greater separation of church and state than the federal Establishment Clause mandates is not compelling in the First Amendment context."
For a more detailed analysis, you may read the opinion here, which is binding on the Court hearing the lawsuits for USR, Mahwah, Montvale and Jackson.