The three opposition parties want to push through a law change requiring a referendum even if the centre-right majority wins the upcoming election.
“I am presuming that the centre-right politicians will respect what Stockholm residents think in a referendum,” Social Democrat leader Mona Sahlin said.
Left Party leader Lars Ohly went as far as to threaten to freeze state funds to the project, reported to be earmarked at around 5 billion kronor, if a centre-right controlled Stockholm did not follow a referendum decision to spend the money on public transport instead.
The proposal is part of a broader package of compromises announced by the parties covering infrastructure investments in the Stockholm region.
According to their agreement, a referendum would be held on September 23rd 2012.
The proposal intends to give Stockholm residents two alternatives – to expand public transport with new rail tracks, metro lines and stations, or to build a north-south motorway route around Stockholm, the so-called Bypass Stockholm.
The compromise signals a new retreat by the Social Democrats in Stockholm who have previously stated their intention to push through the bypass in defiance of opposition from the Green and Left parties.
“The slapdash construction continues,” Prime Minister Fredrik Reinfeldt said in response to the opposition agreement.
“They put inability to work together properly and reach compromises ahead of the Stockholm region’s and Sweden’s important investments in the future,” he said.
The project was given the green light by the centre-right government last September after the completion of an environmental review. Construction of the road is scheduled to commence in 2010 and be completed in approximately eight years.
The road link will span 20 kilometres of roadway, 17 kilometres of which will be by tunnel, and will connect the Stockholm region’s southern and northern areas – from Skärholmen, south of Stockholm, to Häggvik in the north – passing to the west of the city and designed to relieve the heavy traffic around Essingeleden.
The bypass project has been heavily criticised on environmental grounds over the years of its planning. Aside from the Green and Left parties, the Swedish Environmental Protection Agency (Naturvårdsverket) is among those critical of the plan, arguing that it would lead to an 80 percent increase in carbon dioxide emissions in the Stockholm region by 2030.