N.J. Stat. Ann. § 27:14-38

If all the owners of property abutting on any road or highway which has not been improved or is not undergoing improvement, desire the road or any section thereof to be improved, and shall certify in writing to the board of chosen freeholders of the county, that they are willing to bear the entire expense thereof, the county engineer or another competent engineer, shall prepare plans, cross sections and specifications for the work and shall submit them to the property owners. If the property owners are satisfied with the plans, cross sections and specifications they may enter into contract for such work, but the contract shall first be submitted to the board of chosen freeholders for its approval.