The construction of the European route E 661 Gradiška – Banja Luka was contracted in December 2002, and the first works began in the fall of 2004. The section of the highway from Glamočani to the Banja Luka Airport, or to Mahovljani, was built, with a length of 5.7 kilometers. In the mentioned section, 2 tunnels, two bridges and viaducts, an overpass, 2700 meters of service roads were built, and a closed water drainage system from the highway was installed.

This was just the beginning, because in the future, the road to Gradiška, or to the location of the new bridge over the Sava River, in the town of Čatrnja, was to be built. The remaining part of the highway was built through three LOTs, with a length of 26 kilometers.

The first LOT is characterized by the construction of a complete highway, with all accompanying elements, an overpass, and a pair of bridges. In this section, the "Čatrnja" loop was built for the connection to Gradiška and Kozarska Dubica, the "Lužani" rest area, and the Jurkovica bridge. The contractor was a consortium consisting of the companies "Konstruktor" Split and "Integral Engineering" Laktaši.

The second section is characterized by three pairs of bridges, four overpasses, two bridges on local roads, as well as one underpass and the "Nova Topola" loop, while the third section has two bridges and a loop, and the "Aleksandrovac" rest area.

However, the most significant and, according to many, the most beautiful facility on the E 661 Gradiška - Banja Luka highway is the "Mahovljani" loop. This is a grandiose facility, connecting two highways – the E 661 Gradiška-Banja Luka highway and the “9. January” Banja Luka-Doboj highway, which was not yet under construction at the time of the opening of the “Mahovljani” Loop.

The E 661 Gradiška-Banja Luka highway, with a total length of 34 kilometers, was opened to traffic on November 30, 2011, and the “Mahovljani” Loop on July 15, 2012.

Since no toll collection was planned on the E 661 highway, the Public Enterprise “Autoputevi Republike Srpske” carried out activities in 2014 to design, build, and equip a front toll station “Jakupovci” on the busiest section – the bypass around Laktaš. It was an open toll collection system, put into operation on 16.03.2015.

With the construction and opening of the Banja Luka - Doboj motorway, the conditions were created for the construction of a closed toll collection system, and to that end, the design, provision of building permits and contracting for the construction of side toll stations on the "Aleksandrovac" loop and the "Nova Topola" loop were carried out, as well as the front toll station on the motorway in the town of Čatrnja. With the opening of these toll stations, this section of the motorway is charged according to the kilometers traveled.

With the introduction of toll collection, the activities of the public company have expanded significantly, and, in addition to significantly increased revenues, which enable further investments in the design and construction of new sections, it has also enabled the employment of a larger number of people, mainly local residents from Laktaš, Prnjavor, (Gradiška), and Doboj. This, in addition to better connectivity, faster and safer travel, has also achieved direct benefits for local communities in the form of employment of local labor and small and large local companies that worked on the construction.

Two rest areas, "Aleksandrovac" and "Lužani", have been built on the Gradiška - Banja Luka section. The "Lužani" rest area was given under concession, a gas station with accompanying facilities was built, and it was put into operation in June 2025.

As a natural continuation (or completion) of this project, a new interstate bridge was built on the Sava River near Gradiška, completed in October 2022. The bridge is 426 m long and 22.5 m wide, with a steel span structure, 2 + 2 lanes, which, on the Republika Srpska side, continues onto the constructed Gradiška - Banja Luka highway.

The new border crossing and customs terminal on the Bosnian side was built by the ITA in 2018, but until the construction of the access, expressway, and border crossing on the Croatian side was completed, it was in operation only as a customs terminal.

By the end of 2025, all works on the construction of the access, expressway, as well as works on the construction of the new border crossing on the Croatian side, were completed, thus creating the conditions for the new bridge to be fully functional. Since, due to political reasons, the opening of the new border crossing was postponed, the new bridge, as well as a part of the highway from Čatrnja to the border, was only opened to traffic in May 2026.