SPECIAL machines that will build the Mersey Gateway road deck between the three bridge pylons are taking shape.

The giant blue form traveller machines are being assembled at the north and south cofferdams in the Mersey estuary.

They will act as movable concrete moulds for the bridge deck spans and work in a similar way to the movable scaffolding system, which is building the elevated approach viaducts.

Once built, the machines will be lifted by a hydraulic system and fixed into place at either side the bridge pylons to cast the first part of the deck.

The form travellers will then separate and move to the next span position and the process will be repeated, allowing the deck to ‘grow' from each side of the pylon until the main bridge deck is complete.

After the third deck segment has been cast from the bridge pylon, it will then be connected to a stay cable and the upper pylon for support.

Three pairs of form travellers are being assembled, one for each bridge pylon.

The machines are expected to start work in the spring.