Interfax reports, a deep tunnel under the central part of Moscow needs to be built for MCD-5 line. Agency quotes Denis Vlasov, deputy head of the transport and engineering center of the Institute of the General Plan of Moscow. "The main difficulty in organizing a transit route is associated with the need to build a deep and long railway tunnel in the city center," Vlasov told.

According to the official, final decision to build the costly tunnel is not there yet.

MCD is a new transport system of the Moscow metropolitan area to connect the city with the environs. The routes will connect the territories of Moscow and the nearest Moscow region. 52 km MCD-1 "Odintsovo-Lobnya" ("Belorussko-Savelovsky")  and 80km MCD-2 "Nakhabino-Podolsk" ("Kursk-Rizhsky") opened in 2019. Three more diameters to be launched by the end of 2024.

https://www.interfax.ru/moscow/718538

graphic: Government of Moscow press office