New Jersey Transit's director defended the use of audio surveillance systems on some of its trains Tuesday, as some questioned the monitoring's legal and ethical underpinnings.

Audio and video recording currently is in use on the agency's River Line between Trenton and Camden and will be in use on similar light rail trains in Newark and in Hudson County, NJ Transit said Tuesday.

Interim Executive Director Dennis Martin, who will be replaced by a new executive director in two weeks, said the agency is using whatever tools at its disposal to "deter criminal activity" and keep passengers safe, citing global terror attacks.

"In light of terrorist attacks on mass transit facilities around the world, New Jersey Transit is availing itself of the latest technology to deter that, always keeping in mind the privacy rights of our customers," he said.

Martin declined to answer questions about how the audio data is stored and for how long, who reviews it and how it is disposed of. He only added that "there are laws that govern that and we're in compliance."

The American Civil Liberties Union of New Jersey has raised questions about the monitoring, though it has not formally challenged it.

"There are laws that say you can't surveil conversations that you aren't a part of, when a person has a reasonable expectation of privacy," said Ed Barocas, ACLU New Jersey legal director. "If you get a call from your doctor or from children or a spouse and you look for an isolated area of the train where you no one can hear you, you don't expect the government to be listening in."

A New Jersey Transit spokeswoman said the agency has no plans to put audio and video monitoring on its heavy rail lines. NJ Transit's buses are equipped with audio and video surveillance systems but those have to either be activated by the driver or are activated by a collision, a spokesman said Tuesday.

Barocas was skeptical of the utility of monitoring potentially thousands of conversations to combat terrorism.

"Terrorism is really a red herring," he said. "You don't look for a needle in a haystack by just creating an immeasurably larger haystack."