Read the info via this link ( see Port Authority Carpool Plan section )
http://www.panynj.gov/commutingtravel ... tml/ezpass.html#discounts

The carpool plan allows you to cross major bridges/tunnels between NJ/NY and pay $2.00 when you have at least 3 people in the car. You must use the cash lane and inform the toll collector that you have carpool plan.

You need to call ezpass customer service: 1-800-333-TOLL (8655) to enroll in the plan.