An annual franchise tax is hereby levied upon all railroads operating within this State, which shall be assessed at the rate of 10% upon the net railway operating income of the preceding year, computed and allocated in the manner hereinafter provided, of each system and of each railroad not part of a system, provided, however, that the minimum franchise tax payable by any taxpayer shall be $100 as to taxpayers having total railway operating revenues of the preceding year allocated under section 14 not in excess of $1 million and $4,000 as to all other taxpayers.
N.J.S. § 54:29A-13