In a statement, the two partners said they would offer 23 euros a share, which represents a premium of 36.3% over the average share price of Atlantia over the past six months.
The premium stands at 24.4% when calculated over Atlantias share price on April 5, before rumours about the offer fuelled gains. The shares closed up 0.8% at 21.89 euros each on Wednesday, having gained roughly a fifth over the past 10 days.
Shareholders who tender their shares will still receive a proposed dividend of 0.74 euros a share, the bidders said.
The bid comes as Atlantia prepares to pocket 8 billion euros from the sale of its Italian motorway unit, a deal aimed at ending a political dispute sparked by the 2018 deadly collapse of a motorway bridge.
The Benettons, who own 33% of Atlantia, last week said they were in talks with Blackstone after they rejected an approach by Global Infrastructure Partners and Brookfield to acquire Atlantia and hand its motorway concessions to Spains Florentino Perez.($1=0.9163 euros)
