Meanwhile, Premier Paolo Gentiloni said the collapse showed the need for tighter "controls", but that overall the Italian road motorway system was "good".
The premier voiced the hope that a probe into the collapse would clarify accountability for the accident.
The bridge collapsed onto the A14 motorway near the central Italian city of Ancona, killing two people and injuring three others.
The victims were identified as Emidio 'Mimmo' Diomedi, 60, and his wife Antonella Viviani, 54, who had been married for 36 years.
Autostrade said it had "asked with extreme urgency the firms that designed and carried out the works on the bridge for a detailed report on what happened, to establish possible human errors and weigh possible legal action".
The bridge was a temporary structure to support an overpass that had been closed to traffic during works to broaden the highway between the South Ancona and Loreto exits to three lanes.
Opposition politicians said the collapse, which followed others in recent years, was "unacceptable", and that traffic should have been stopped beneath the bridge while the work was being carried out.
With ANSA
