Trucks that haul gaseous hydrogen are called tube trailers. Gaseous hydrogen is compressed to pressures of 180 bar (~2,600 psig) or higher into long cylinders that are stacked on a trailer that the truck hauls. This gives the appearance of long tubes, hence the name tube trailer.
Tube trailers are currently limited to pressures of 250 bar by U.S. Department of Transportation (DOT) regulations, but exemptions have been granted to enable operation at higher pressures (e.g., 500 bar or higher). Steel tube trailers are most commonly employed and carry approximately 380 kg onboard; their carrying capacity is limited by the weight of the steel tubes. Recently, composite storage vessels have been developed that have capacities of 560–900 kg of hydrogen per trailer. Such tube trailers are currently being used to deliver compressed natural gas in other countries.