N.J. Stat. Ann. § 39:6A-4.1

When a named insured is the owner and only designated operator of two or more automobiles and the only licensed driver residing in the household, he shall be charged a reduced personal injury protection premium for each automobile listed in addition to the principal automobile on the policy in an amount determined by the commissioner for the benefits provided in section 4 of P.L.1972, c. 70 (C. 39:6A-4). Three years after the initial reduction in such premiums the personal injury protection premium for such additional automobiles shall be determined by the loss experience of the rate filer with respect to the payment of personal injury protection benefits which are attributable to such additional automobiles.