The income remaining after allocation for the following companies must be apportioned using the following factors:

(1)(a) Railroad companies shall use a fraction in which the numerator is railway operating revenue from business done within this State during the taxable year and the denominator is total railway operating revenue from all business done by the taxpayer as shown by its records kept in accordance with the Uniform System of Accounts prescribed by the Interstate Commerce Commission.

(b) If the department finds that the accounting records of a taxpayer do not accurately reflect the division of revenue by state lines as to each transaction involving interstate revenue, the department may adopt rules and promulgate regulations which determine averages which approximate with reasonable accuracy the proportion of interstate revenue actually earned upon lines in this State.

(c) For purposes of this item:

(i) "Railway operating revenue from business done within this State" means railway operating revenue from business wholly within this State, plus the equal mileage proportion within this State of each item of railway operating revenue received from the interstate business of the taxpayer.

(ii) "Equal mileage proportion" means the proportion which the distance of movement of property and passengers over lines in this State bears to the total distance of movement of property and passengers over lines of the taxpayer receiving the revenues.

(iii) "Interstate business" means railway operating revenue from the interstate transportation of persons or property into, out of, or through this State.

(2) Motor carriers of property and passengers shall use a fraction in which the numerator is vehicle miles within this State during the taxable year and the denominator is total vehicle miles everywhere during the taxable year.

(3) Telephone service companies shall use a fraction in which the numerator is gross receipts in this State during the taxable year and the denominator is total gross receipts everywhere. The term "gross receipts in this State" includes gross revenues derived from services rendered wholly within this State, plus that portion of the company’s interstate revenues attributable to this State in accordance with the Federal Communications Standard Classification of Accounts.

(4) Pipeline companies shall use a fraction in which the numerator is the revenue ton miles (one ton of solid property transported one mile), revenue barrel miles (one barrel of liquid property transported one mile), or revenue cubic foot miles (one cubic foot of gaseous property transported one mile) within this State during the taxable year and the denominator is the total revenue ton miles, revenue barrel miles, or revenue cubic foot miles, of the taxpayer everywhere during the taxable year.

(5) Airline companies shall use a fraction in which the numerator is revenue tons loaded and unloaded in this State during the taxable year, and the denominator is revenue tons loaded and unloaded everywhere during the taxable year. A revenue ton is a short ton (two thousand pounds) and is computed by using a standard weight of one hundred ninety pounds a passenger (including free baggage) multiplied by the number of passengers loaded and unloaded plus the tons of airmail, express, and freight loaded and unloaded within and without this State.

(6) Shipping lines. Where the income is derived principally from the operation of a shipping line, the corporation shall apportion its net apportionable income to South Carolina on the basis of the ratio of revenue tons loaded and unloaded within and without the State for such year. A revenue ton is a short ton (two thousand pounds) and must be computed using a standard weight of one hundred ninety pounds per passenger (including free baggage) multiplied by the number of passengers loaded and unloaded.