The work in question is included within the more general modernization of the existing two-lane route between Sassari and Olbia (total development of approximately 75 km), with adoption of a section type B according to the DM 05/11/2001.
The Sassari-Olbia road  is the main internal cross-connection between the western and eastern coast of the North of Sardinia. It is strategic for the development and growth prospects of the 'island, considering that it connects two major cities of northern of Sardinia, two ports (Olbia and Porto Torres) and two airports (Olbia and Alghero).
To date, the connection is represented by a single carriageway in two lanes (one for each direction) and lateral margins of different amplitude; it is characterized by rather low traveling speed (up to 80-90 km / h max), with junctions often realized through intersections.
In detail, the fourth lot provides for an adjustment in plano-altimetric variation of the existing road SS 597 for a development of approximately 9.5 km, from km 36 +100 to km 45 +610.
Functional and geometric characteristics
Main road
The rays of the curves, always higher than 1200,00 m, always ensure the maximum design speed Vp, ​​max = 120 Km / h, in addition to the visibility distance in correspondence of the left-hand curves without the need for enlargement of the road platform. The altimetric trend has been defined by grade lines with slopes less than the maximum prescribed.
Sections type B according to the Ministerial Decree 05/11/2001
The road platform has a width equal to 22,00 m., with two lanes from 3.75 m. in each direction, rights roadsides by 1.75 m., left roadsides by 0.50 m. and median strip of 2.50 m.
The main artworks
In the lot in question there are three flyovers, and are planned 7 bridges/ viaducts, including 4 on the main axis and 2 on the secondary roads

Rio Mannu overpass bridge (km 41+181)

The design solution provides for the adoption of a continuous pattern, with steel deck and with calculation lights of (axis support) equal to 41.5 m. The decks are linked to substructures with elastomeric isolators.