The Social Democrat and Green Party government had earlier wanted to delay the project until 1 May, in order to negotiate financing and the role of public transport.
But now the project will begin 1 January, say Social Democrat Infrastructure Minister Anna Johansson and Green Party Environment Minister Åsa Romson, at a press conference Thursday morning.
Left Party leader Jonas Sjöstedt is disappointed with the Green Party.
"Sad that the Greens capitulated on the bypass, when we need to switch from roads to rail. The government's climate policy is a big disappointment," Sjöstedt wrote on Twitter.
Last week a majority in the parliament's traffic committee - consisting of the conservative Alliance parties and the xenophobic Sweden Democrats - supported a motion to resume construction on the bypass by 1 January 2015.