The extension of or addition to a private way constructed on or before June 9, 1998, which provides vehicular access to serve additional lots or additional principal uses which were not served by the existing private way, in combination with an existing private way, which is more than 500 feet in length (such length shall be measured from the terminus of the portion of an existing private way which meets the approval criteria set forth in this chapter in Article XIV, § 290-14.4, or, in the event that no portion of the existing private way meets those approval criteria, then such length shall be measured from a Town road or approved subdivision right-of-way which does meet the approval criteria set forth in that section of this chapter).