N.J. Stat. Ann. § 39:4-98.1

In accordance with the provisions of section 39:4-98 of the Revised Statutes, the State Highway Commissioner may, by regulation and identification by appropriate signs, designate lower maximum speed limits for trucks of a registered gross weight of 10,000 pounds and over, at a differential of 5 miles per hour, on State highways, or appropriate portions thereof, having 4 or more traffic lanes, where the legal speed limit is 50 miles per hour or greater.