Abnormal and escorted loads

How does Abnormal and escorted loads work, step by step?

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   Step 1: Survey the route before the component is designed

   A physical route survey is carried out from the factory to the site, usually by the specialist haulier, covering restricted widths, headroom under bridges and overhead services, the capacity and condition of structures, turning radii and swept paths at junctions and roundabouts, gradients, street furniture, and anything on the route that would have to be moved or lifted. The survey produces an envelope - a maximum width, height, length and weight that can realistically reach the gate - and that envelope goes to the designer as a design constraint. Doing this early is the whole discipline: the route is designed before the module is.

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   Step 2: Design the component inside the envelope

   The designer works to the envelope, deciding how the building is divided into modules, where the joints fall, and how each module is proportioned. Where the envelope is tight the answer may be narrower modules and more of them, or splitting a module and completing the joint on site. The lifting points, the temporary stiffening needed to keep the module square in transit, and the transport restraint arrangement are designed at the same time, because a module that is adequate in the building can be a flexible box on a trailer.

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   Step 3: Let the haulier and the authorities determine the permissions

   The specialist haulier assesses the completed load - dimensions, mass, axle arrangement and vehicle configuration - and applies for the permissions that movement requires. The relevant highway and police authorities determine what notice is needed, what conditions attach, whether escorts are required and of what kind, what route must be followed and at what times it may be travelled. The operators of bridges and other structures on the route determine what they will accept and on what terms. None of this is assumed or carried over from a previous project, and the programme allows for the process taking time.

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   Step 4: Plan the movement in detail

   The agreed route is planned movement by movement: the departure time, the running speed, the holding points where the load can stand safely, the junctions requiring a manoeuvre, the points where street furniture must be removed and reinstated, and the arrangements with any utility operator whose overhead lines must be lifted or isolated. Communications are set up between the escort, the driver and the receiving site so the project knows where the load is. A contingency plan covers breakdown, an obstruction on the route and a delay that pushes the movement outside its permitted window.

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   Step 5: Prepare the receiving end

   The site prepares for a vehicle that cannot improvise. The gate, the approach and the standing position are checked against the swept path of the actual vehicle, temporary works are provided where the vehicle must stand on made ground or near an excavation, and the crane is positioned and its lift plan prepared for that specific component. Where a self-propelled transporter is to be used on site, the surfaces it will run on and the bearing capacity beneath them are designed. Everything that can be done before the load arrives is done before the load arrives, because a large module standing on a public road is a problem measured in minutes.

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   Step 6: Load, restrain and check at the factory

   The module is loaded at the factory using its designed lifting points, positioned on the trailer as the transport arrangement requires, and restrained to the haulier's scheme. Protection, sheeting and any temporary stiffening is fitted and checked. Dimensions and mass are verified against what the permissions were applied for, because a load that has grown since the application is an unpermitted load. Markings, lighting and any required signage are fitted before departure.

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   Step 7: Move the load, commonly at night

   The movement runs to the permitted route and timing, which for large loads frequently means overnight or in the early hours when traffic is light and junctions can be worked. Escorts control traffic at the points identified in the plan, street furniture is removed and reinstated as agreed, and progress is reported to the site so that the crane and gang are called in at the right time rather than standing from midnight. The driver and escort stop the movement if anything on the route differs from the survey.

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   Step 8: Receive, inspect and lift

   On arrival the module is checked against the paperwork and inspected for transit damage and distortion before restraints are released, with particular attention to squareness, to glazing and finishes, and to the lifting points. The lift then proceeds under the lift plan prepared for that component, and the vehicle is released and taken off the highway as quickly as the operation allows. Any damage or dimensional change found is recorded and referred to the designer before the module is built into the works.