Outline

Kehä I is a congestion-sensitive main traffic route in the Helsinki metropolitan area, with normal daily traffic ranging from 45,000 to 50,000 vehicles. Traffic volumes are expected to continue increasing. In a project that began in 2019, improvements were made to enhance the flow and safety of traffic on Kehä I, particularly in the Laajalahti area. This project also enabled the implementation of the Raide-Jokeri express tram, an important cross-traffic connection for the Helsinki metropolitan area, near Kehä I. Objectives were also to improve safety and noise protection for transportation and to consider environmental values. The project was completed in September 2021.

The project is located by the sea close to a natural reserve. Due to these characteristics, special attention was paid to natural conservation and flood protection. Since the route is one of the main traffic routes climate bound hazards were considered including frost protection, protection against falling rocks and storm water management.

Resilience assessment

In the project planning, the typical cross-factors of the area were considered, such as flood risk areas, heavy rainfall, extreme weather events, freeze-thaw impacts on structures and the changes caused by the project to the nearby nature conservation area. Various risk factors were considered in the sizing of structures, including stormwater management and roadway drainage, as part of the resilience assessment.

How are adaptation solutions considered?

Stormwater and heavy rainfall management involved the use of stormwater depressions. These depressions were also utilized for temporary water management during construction and to prevent runoff from affecting the maritime nature conservation area.

The purpose is to regulate water flow, delay stormwater, and minimize flood risk for properties downstream of the ditch. This measure also ensures that the pedestrian and cycling connections of Ruukinranta’s underpass remain accessible even during heavy rainfall. The required retention volume for the constructed depressions has been calculated based on a once-a-year recurring heavy rain situation, which amounts to approximately 280 m3. The upper edges of both stormwater depression slopes and the basin bottoms will be allowed to naturally vegetate.

The hazards associated with the freeze-thaw cycle on steep rock excavations were identified in the vicinity of a pedestrian pathway. It was observed that a rock wall was susceptible to the effects of climatic variations, potentially leading to a deterioration in its structural integrity, thereby posing a hazard to users of the pathway. To address this issue, a 300-meter-long and up to 6-meter-tall rock wall was safeguarded and reinforced with a stone retaining wall. This measure aimed to safeguard pedestrians from the risk of falling rocks and to mitigate the adverse effects of climatic conditions.