All vehicular access to and from any lot on which a business or commercial building or use is located (including accessory off-street parking spaces) shall be through designated driveway openings having a width of not more than 20 feet at the exterior line of the public or private way, and not more than one opening for entrance and one opening for exit (which may be contiguous with a total width of 40 feet) shall be permitted along any way for each 200 feet of lot frontage on said way, if in a General Business District, or for each 300 feet of lot frontage on said way, if in a Commercial & Industrial District. In the case of a lot having less than the specified frontage along the exterior line of way, a total of not more than two designated driveway openings shall be permitted (one of which shall be for entrance and the other for exit), provided that:
A. Said lot was laid out by deed or conveyance or shown on a duly recorded plan prior to the effective date of this bylaw (October 1, 1958), provided that on such date said lot did not adjoin other land of the same owner available for use in connection with said lot; or
B. Said driveway openings are used or to be used in common by two or more lots having a total continuous frontage on the way of at least the amount specified for a single lot; or
C. Said driveway openings are at the exterior line of a private way whose primary function, in the opinion of the Zoning Board of Appeals, is to provide access to premises located in nonresidential districts, and a variance from these requirements is accordingly authorized by said Board.