Buying Guide For DOT 406 Compliant Tank Trailers

DOT 406 tank trailers are typically used for hauling and transporting gasoline and other highly flammable liquids. These tank trailers are usually composed of aluminium and have a heavily constructed top that is excavated to hold small spills. These tanks are generally separated into three to four compartments, with one hatch per compartment in the tank, and they feature one or more domes or hatches and dome coverings. DOT 406 tank trailers are elliptical when looking from the rear and have an oval shape with flat and nearly flat ends and have a maximum hauling capacity of 9000 gallons.

What is DOT 406 certification/compliance?

Certification is a very essential asset for DOT 406 tank trailers, at or before the time of delivery, the manufacturer of DOT 406 tank trailers must provide documents to the owner of the tank trailer. This certificate should carry important information such as manufacturer registration number, design certifying engineer and the registered inspector. A certificate is signed by a manufacturer's supervisory official and a Design Verifying Engineer for each and every variant type, certifying that the tank trailer design fulfils the relevant DOT 406 compliance specification.

How to test for DOT 406 compliance

DOT 406 compliance test is an essential part of making the certification documents. This test mainly includes pressure test, material thickness test and other advanced level tests such as hydrostatic and pneumatic tests.

  • Pressure test: The MAWP (Maximum allowable working pressure) of each tank trailer must be no lower than 2.65 psi and no higher than 4 psi. Pressure tests are a non-harmful way to assure the integrity of the tank trailer. The piping codes demand that a piping system is to be strong to sustain its rated pressure and has no leaks. The ASME B31 Pressure Piping Code is the most extensively used code for pressure and leak testing.
  • Material thickness test: This test identifies the quality and the thickness of the material that is used in the construction of the tank trailer. Therefore, material thickness is required to fulfil the equivalent DOT406 specification's structural strength and accident damage standards.

Hydrostatic and pneumatic tests are the advanced level pressure testing of tank trailers which are done by the manufacturers, once the trailers are over with the typical testings.

Types of DOT 406 trailers?

  • Straight Bottom / Elliptical Trailers: Straight bottom tank trailers are used to haul low consistency items like fuel and different flammable liquids in almost any kind of environment. These tanks can be filled more quickly, and several compartments can be loaded at the same time.
  • Double Taper Trailers: This design allows the trailer to drain completely and quickly in level environments. It is multi-functioned enough to be used in hauling different fluids, the double taper design is best in unloading high viscosity products, like lubricants.
  • Trough Bottom Trailers: This type of trailer is designed to drain quickly in the most challenging environments. The surge baffles act as dams that slow the flow of liquid in a conventional straight bottom or double taper trailer. The trough bottom trailer excels in the unloading of low viscosity fluids such as gasoline, ethanol, diesel and solvents as it bypasses the surge baffles present in most compartments by allowing the product to flow unobstructed to the unloading sump.

Types of loading systems in DOT 406 Trailers?

DOT 406 tank trailers have two types of loading systems. Fuel or liquid can be loaded from either the top or bottom. Each option has advantages and disadvantages.

  • Top Loading:It is unsafe and dangerous to load fuels or liquids from the top. When gasoline is loaded from the top, it evaporates into the atmosphere. The presence of vapor or fumes at the filling station raises the danger of explosions. That is why top loading is not recommended for flammable liquids.

    Furthermore, the gas that has evaporated represents a reduction in the tank's overall volume. Top loading is equally hazardous to employees or workers and should be avoided under all circumstances for safety concerns. Additionally, top-loading takes time as compared to bottom loading.
  • Bottom Loading:Bottom loading is advised for all forms of fuel such as petrol, diesel and other flammable liquids. Bottom loading is faster, safe and more reliable than top-loading. It has a low risk of any incident and explosion at the filling station. Gasoline vapor remains within the internal circulation. Bottom loading is considered the safer loading for the workers.

Design Configuration

Tanker trailer design is one of the vital aspects when it comes to safety and stability. DOT 406 tank trailers come in different types of shapes, such as circular, ellipses and rectangular. Because of the necessity for stability, Large DOT 406 tank trailers have an elliptical and circular rectangular form. These shapes have a low centre of gravity which makes the tank trailer stable. The ratio of their height to gravity is 1:0.79:0.65. On the other hand, high-pressure tanks are constructed in the shape of a circle which enhances the stability of the trailers.

Products suitable to haul in a DOT 406 trailer?

The DOT 406 tank trailer is meant to transport low-flashpoint fuels and flammable liquids, including gasoline, diesel, biodiesel, E85, ethanol, methanol, racing fuel, aviation fuel, AvGas, and Jet-A, as well as chemicals like alcohol. DOT 406 is a perfect choice for hauling these types of products.

What are the inspection requirements of the DOT 406 tank trailer?

A tank trailer built in accordance with a DOT 406 compliance standard that has become due for a test or inspection specified in this section may not be filled and offered for transportation or moved until the test or inspection has been successfully performed. There are types of inspection measures such as FHWA inspection (tires, brakes, and lights), Internal visual inspection (baffles and other internal compartment), vapor tightness inspection, pressure test, leakage test and external visual testing. After all these inspections, the inspector records all the results and approves the tank trailer and gives the green light for transportation.

What are the specifications of DOT 406 Tank Trailers?

The DOT 406 tank trailers are usually used for transporting fuel and other flammable liquids. These trailers are usually built with two types of materials which are aluminium and stainless steel which provides high built quality to the tank trailers. These trailers are divided into 3-4 compartments for better stability in transportation. The general specification of DOT 406 compliant are as follows:

  • Maximum operating pressure of up to 4 psi
  • Oval or a curved cross-section
  • Flat or almost flat ends
  • The primary material is aluminium in construction
  • Typically Multi-compartmented
  • One manhole for each compartment
  • Emergency shutoff
  • Rollover protection
  • Average a maximum capacity 9,000-9500 gallons for a tandem

All these specifications can make a perfect DOT 406 tank trailer that meets the federal specification requirements for the transportation of fuel and other gasoline liquids.

What are the federal requirements of DOT 406 Trailers?

A DOT 406 tank trailer specification complies with the federal guidelines for transporting gasoline and avgas on public highways in bulk quantity, as defined by the government. There are some federal specification requirements for DOT 406 such as It should operate at a maximum pressure of 4 psi and must fulfil a variety of different requirements that help in the prevention of major accidents. A separate hatch for each compartment, an immediate cutoff on the driver's side front, and rollover prevention to prevent the hatch from opening during a rollover. DOT 406 compliant is authorized for the hauling of Gasoline and other fuels on public roadways as per federal transportation requirements. The US transport legislation governs the transport of flammable products, such as fuel and gasoline, specifies that the transportation of Gasoline including other fuels with flashpoints lower than 38-degree Celsius are suitable with DOT 406 tank trailers.

What are the safety features loaded in DOT 406 trailer?

Nowadays manufacturers are continuously improving tank trailer safety equipment for the prevention of road accidents and contributing safety to the hazardous cargo sectors.

Several manufacturers, including Civacon, Emco Wheaton, Girard Devices, Alpeco, Betts Industries, Dixon Bayco, and Scully, have designed safety equipment for tank trailers, this equipment includes,

  • Highly engineered manlids/manholes
  • Vapor recovery system
  • Foot, emergency, and internal valves
  • Electronic stability control (ESC) systems


Roll-over mechanisms are installed in the manlids on the top of the tanker, which close the aperture in the case of a rollover. The risk on the top of the tanker is that the expansion and contraction of the gasoline liquids imply that each compartment must be allowed to breathe, otherwise the pressure in the tank would catastrophically shatter it.

There would be an apparent leak channel for the liquid to escape if the tanker rolled over, which might result in a fire or an environmental disaster. This rollover mechanism in the manlids can stop the leakage of liquid which prevents environmental disasters or tanker explosions.


Gasoline compounds are flammable which requires the use of a vapor recovery system in the tank trailers. The vapor recovery system is a set-up designed to remove harmful and unwanted vapor from the fuels, rather than causing build-ups in tanks. It also increases purity and prevents hazardous pollutants from entering the environment.


These valves transfer the product into the tank trailers as part of the product transfer process. They're also meant to act as 'weak or break' points below road tank trailers, shearing off and securing the liquid load in the occurrence of a rollover or other accident.


ESC systems have been applied to the tank trailers industry in recent years. These intelligent systems can detect a rollover or lose directional control and can apply the tanker's brakes safely to prevent an accident.

To conclude, when it comes to DOT 406 tank trailers, there are different types of trailers in the list such as the straight bottom, double taper and trough bottom trailers. These trailers have their own specific designs to meet various customer and business requirements. The customer needs to fully understand all the vital considerations and specifications, federal requirements, certificates, inspection approvals, compliance tests and safety features in the process of purchasing the DOT 406 tank trailer. These documents and information is a very essential part of buying any type of DOT 406 tank trailer. If you have all this information about DOT 406 specifications, you can choose to pick a type as per your business requirements. If you want to know more information about tank trailers or if you’re ready to check out some of the best fuel tank trailers for sale in Houston, Texas, get in touch with the sales department at Trailers of Texas.

Call Now