The Lahti southern ring road on main road No 12 improves the flow of traffic and the comfort of the residential environment

The safety of the road and street network and the flow of traffic in Lahti and Hollola improved significantly when the Lahti southern ring road was completed. The new highway between Soramäki and Okeroinen diverted long-distance heavy traffic away from the streets in the city. The environmental impact was also significant. The risks of groundwater contamination were substantially reduced as transit traffic was diverted away from the extremely important groundwater area of Salpausselkä.

The road we built in completely new terrain enables the development of land use in central Lahti and Hollola and the development of the diverse environment around the station of the Lahti Travel Centre, which supports the region and international traffic. The new road connection is an important part of the road network for special transport, and it also significantly improves the accessibility of the Nostava logistics area.

We built approximately 9 kilometres of new national highway around eight kilometres of which as single-lane and one kilometre as two-lane road. The project included the construction of 18 new bridges and grade-separated junctions in Soramäki, Nostava and Okeroinen. We also improved noise protection and traffic connections for pedestrians and cyclists.

Large overall responsibility made it possible to find optimal solutions

We executed the project as a Design and Build (DB) contract. Since we were also responsible for the design, the contract type meant greater overall responsibility for us. This provided more opportunities than usual to explore the most optimal solutions for project implementation. Model-based production played a key role in the project. It enabled the successful completion of the project, both in terms of scheduling and quality.

We also took into account the environmental impact and biodiversity. We built sunlit slopes for endangered plant and butterfly species and a nature-like underpass pipeline for small animals. We minimised emissions from the transportation of surplus soil by, for example, good construction design and active work planning.

We made extensive use of our diverse expertise in the project. Our road designers were in charge of designing the road alignment, and our bridge designers designed six new bridges, two bridges to be repaired and three pile slabs.

Our expertise in geotechnical design was also actively used. Our central insight was to partly replace the pile slabs with preloading and loading embankments and lightening measures. This was enabled by extensive additional studies carried out to determine the exact soil parameters and to check the calculations. The preloaded embankments already settled during the work, which will prevent the road from settling in the future, even though we left out some of the pile slabs. Bridge geotechnology was also challenging with regard to steep elevation differences in terrain and demanding bridge piles.

The project 1A we executed was part of a group of projects, which included the construction of the Lahti southern ring road on main road No 12 (projects 1A and 1B) and the improvement of the southern access road to Lahti on regional road 167. Work on regional road 167 begun in spring 2017 and on main road No 12 in spring 2018. Main road No 12 was opened to traffic at the end of 2020 in accordance with the target schedule. Finishing work was carried out in 2021 and the final surface layer will be completed in 2023.