N.Y. Comp. Codes R. & Regs. tit. 21, § 1025.10 – Compressed gases.

(a) No vehicle shall enter the Queens Midtown Tunnel, the Brooklyn-Battery Tunnel or the Verrazano-Narrows Bridge Lower Level if its load includes any flammable compressed gas or nonflammable compressed gas listed in section 1025.27 of this Part and referenced to this subdivision, unless such compressed gas is in a tube or cylinder two inches or less in outside diameter and four fluid ounces or less in capacity. Empty containers which last contained--a compressed gas referenced to this subdivision are not allowed passage when the quantity and/or container size limitations exceed those described above. No empty tank vehicle is allowed passage if the vehicle is used for the transportation of any compressed gas referenced to this subdivision.
(b) Except as set forth in subdivision (h) of this section, compressed gases listed in section 1025.27 of this Part and referenced to this subdivision are restricted to a maximum quantity per vehicle of 100 pounds gross weight; provided, however, that the gross weight of each cylinder or tube is 10 pounds or less, and except that cyclopropane or ethylene for hospital use is restricted to a maximum quantity per vehicle of 20 tubes or cylinders measuring 20 inches or less in length, and 4 ½ inches or less in outside diameter. Empty containers which last contained a compressed gas referenced to this subdivision are not allowed passage when the quantity and/or container size limitations exceed those described above. No empty tank vehicle is allowed passage if the vehicle is used for the transportation of any compressed gas referenced to this subdivision.
(c) Pressurized vessels (aerosol or similar type containers) containing a flammable liquid mixture (flash point at or below 100°F) or a combustible liquid mixture (flash point at or above 100°F and at or below 200°F), or a liquefied flammable compressed propellant gas, are prohibited from entering the Queens Midtown Tunnel, the Brooklyn Battery Tunnel or the Verrazano-Narrows Bridge Lower Level, unless such vessel or container be of metal, of 19.3 fluid ounces capacity or less, and have an absolute pressure of 75 pounds or less; and, when so packed in an outside container, the quantity of the total load shall not exceed 4,000 pounds gross weight per vehicle. Vessels containing nondangerous materials that are propelled by nonflammable compressed gases are not restricted, regardless of quantity or size of containers.
(d) Compressed gases listed in section 1025.27 of this Part and referenced to this subdivision are not restricted, regardless of quantity or size of containers. No tank vehicle, loaded or empty, is allowed passage if the vehicle is used for the transportation of any compressed gas referenced to this subdivision.
(e) Liquefied argon, liquefied helium or liquefied nitrogen, when transported in specially constructed tank vehicles under self-refrigeration with less than 40 psi absolute pressure, are not restricted.
(f) Compressed gases listed in section 1025.27 of this Part and referenced to this subdivision are not restricted, regardless of quantity or size of container, or when transported in tank vehicles.
(g) Any article listed in section 1025.27 of this Part and referenced to this subdivision may or may not be a compressed gas. When it is not identified by the prescribed U.S.D.O.T. caution label for hazardous materials—and is known not to meet the description of a hazardous material—the article is allowed passage, provided the shipping order, bill of lading or other shipping paper shows the following certification:
This shipment conforms to Triborough Bridge and Tunnel Authority rules for the transportation of explosives and other hazardous materials via the Queens Midtown Tunnel, the Brooklyn-Battery Tunnel and the Verrazano-Narrows Bridge Lower Level.
(h) Compressed natural gas carried by a motor vehicle for the sole purpose of providing fuel for the vehicle in which it is carried shall not be subject to the limitations of subdivision (b) of this section, provided:
1. (1) such compressed natural gas is stored and carried only in a tank or tanks connected to and forming a part of the fuel system for such vehicle, or in other components of the fuel system of such vehicle; and
2. (2) such vehicle, and each of its component parts, has been designed, fabricated, assembled, maintained, and marked in accordance with all applicable requirements of Federal, State and local laws, rules, regulations, and directives, and industry standards.