Merko has made its contribution to the development of the public transport network of Tallinn through several projects. The extension of tram line 4, which was completed in November 2017, provides rapid connection between the city centre and the airport and, in the future, the Rail Baltic passenger terminal at Ülemiste. The extension to the tram track begins with a turning canyon at St. Petersburg Road, continues through the tunnel under the railway and Suur-Sõjamäe Street, rises to the surface at Keevise Street and ends with a turning loop at the airport. To build the first tram tunnel in Estonia with a 150-metre long covered part and a 125-metre long ramp, 10,000 m³ of limestone and 6,000 m³ of soil was displaced, a total of 1,000 m³ of concrete was cast or installed; an additional 700 m³ of concrete was used for building the tram tracks and load-bearing constructions.