The 7.2km double-track underground line would have branched off the existing line to Helsinki Central south of Pasila, with three new stations serving Töölö, City Centre and Hakaniemi. Construction of the loop would enable the diversion of some commuter services away from the Pasila – Helsinki Central line, easing congestion on the existing line and improving rail access to the central districts of Töölö and Hakaniemi.

The Finnish Transport Agency and the City of Helsinki have completed a general plan and an environmental impact assessment, and an initial public consultation has also been carried out. In 2013 the European Union allocated €5m from the TEN-T programme to fund more detailed studies.

The decision not to proceed with the project could be reversed if there is a change of government following Finland's forthcoming general election, which will be held in May.