Hydraulic modular trailer

There is a limited number of manufacturers who produce these heavy-duty trailers because the market share of oversized loads is very thin when we talk about the over all transportation industry.

There are self powered units of hydraulic modular trailer which are called SPMT which are used when the ballast tractors can not be applied due to space.

[3] In 1962 Cranes Trailers limited developed two four-axle 32-wheel modules for Pickfords, a London based heavy haulage company, with combined payload capacity of 160 tons on a total of eight axles and 64 wheels the modules incorporated hydraulic suspensions and each axle interlinked with mechanical steering system at an operational height varied from 2.9 to 3.11ft.

These trailers had independent suspension and steering abilities via the Petter twin-cylinder diesel engine used as a PPU.

To comply with new regulations and keeping safety in mind, the industry knew that they needed more axles to distribute the payload and the ultimate solution for the demand would be HMTs.

Manufacturers chose high-tensile steel instead of aluminum because when it comes to HMTs and oversize loads, the minimizing the weight of the HMT is not relevant when they have their own payload capacity excluding the ballast tractor.

The number of axles on a HMT is not specified; two-, three-, four-, five-, six-, and eight-axle units are manufactured.

PPU, which powers the steering, suspension to and fro flow of hydraulic fluid from hydraulic tank to suspensions and steering cylinders, puts out about 18 to 25 hp of power and are available in both diesel and petrol variants manufactured by renowned brands like Kohler, Yanmar and Hatz.

HMTs can not move themselves, so There are two ways by which a HMT can be coupled with a tractor unit which can push and pull the trailer, these are gooseneck and drawbar.

[citation needed] Since 2005 in the United States of America, HMT have extra features and design changes which include widening axles, and half way folding system.