Piles are being sunk into the river bed at the site, which is just downstream from O'Connell Bridge.
Dublin City Council is proceeding with the construction that will allow the Red and Green Luas lines to be linked -- despite uncertainty about the project. The new structure will also be open to buses and cyclists.
The bridge was due to begin in late 2009, but was delayed because of funding concerns.
The council said the new Marlboro Street Bridge is needed, in any event, for the bus network.
"It will have cycleways and generous footpaths that will open Marlborough Street and Hawkins Street to greater footfall, prospective development and create a new north-south link from Abbey Street to Pearse Street," said the city council.
The design is described as "elegant contemporary" with the underside as high above the water as possible so river traffic is not impeded.
An Bord Pleanala is due to give a decision by late summer on the Luas BXD. It's been told it would cost nearly €19m to have the line running without overhead cables in the city centre.
Recently, fresh details on plans to link the Dublin city centre Luas tracks were submitted to An Bord Pleanala. The lack of a connection between the Red and Green lines has long been considered one of the most glaring shortfalls in the transport network.
The works comes as the National Transport Authority warned that there is little point in carrying out underground works on the Metro and DART due to uncertainty over funding.