The incredibly deep £3.9bn tunnel riddled with delays that could solve traffic problems

The project could cost upwards of €4.7 billion (Image: Getty)

The £3.9billion Stockholm Bypass has been tipped to be able to solve Sweden's traffic issues - but its construction has been riddled with delays.

Running through one of the fastest-growing cities in the continent, when it is completed it will be one of the longest road tunnels in the world. 

The increasing population in Stockholm has seen the demand for this new infrastructure, which the government hopes will ease pressure on the capital's traffic issues.

Known for its strong economic prosperity, the region has become an attractive destination for young professionals - meaning more cars are getting on its streets.

Over the next 75 years, the city's population is projected to increase by over 43 percent, to nearly 3.5 million residents. Despite Stockholm's sophisticated public transport network, driving remains one of the most popular modes of transportation.

The city is known for its economic prosperity (Image: Getty)

The E4 Bypass (Förbifart) is Stockholm's answer to its congestion problems. The nearly £4bn project, which starts in Skärkholem, spans over 21km, and includes a huge 18km tunnel. 

The bypass will continue up north to Häggvik, and move the traffic west and away from the city centre, where traffic is a large issue.

Traffic will be carried through a twin set of tunnel tubes, which will carry three lanes of cars each, as well as six interchanges that will connect the flow of vehicles to existing roads around Stockholm. 

The tunnels will take drivers at nearly 100m below ground level at its deepest point, and upon its completion in 2030, it will be one of the longest road tunnel systems in the world. However, completing the project has not been easy.

Due to Stockholm's complex make-up, constructing the bypass has been extremely complicated. Engineers have faced issues navigating through the city's waterways and deep underground.

Workers pushed to clear the way for the tunnel systems by drilling rings of holes into the rock, which were injected by cement and water so that water could not seep in through the cracks and flood the system. Further holes were then drilled and filled with blasting material, which were exploded and scraped out to make space for the tunnel network. 

There are 22 million tonnes of rock and sand that need to be excavated for the tunnel system, which will be reinforced with rock bolts, sprayed with concrete and cladded after it is carved out. However, as the underground is made of different types of rock, different challenges were faced by workers at each point. 

Weaker rocks need more reiforcement, whereas other types need more sealing, both slowing down the building process, reports The B1M. In order to protect the workers as they tunnel underground, extensive ventilation systems have been installed, which will also help to protect people in the case of a fire.