Are chemicals in a tank car exempt from threshold determinations under 40 CFR Part 68?

The definition of stationary source does not apply to transportation, including storage incident to transportation (40 CFR Section 68.3).  Are chemicals in a tank car (e.g., tanker truck or rail car) therefore exempt from threshold determination?

The chemicals in the tank car are exempt only if the tank car is in transportation. EPA considers a container to be in transportation as long as it is attached to the motive power (e.g., truck or locomotive) that delivered it to the site (63 FR 643, January 6, 1998). If the tank car is detached from the motive power, and therefore no longer in transportation, the contents of the tank car must be considered in the threshold determination.