Estonia's National Broadcasting News Portal (ERR) writes that Rail Baltic wants to build initially only one tunnel  under the railway to connect Ülemiste with the city center (these tunnels are short ones, you can guess). The Tallinn city had planned to build 5 tunnels with EU money. Rail Baltic does not want to build the remaining 4 because the street network in the area are not known. It means, the tunnels could be useless in the future. Only the westernmost tunnel connecting St. Petersburg Road and Suur-Sõjamäe Street will be built.

Importance of Ülemiste is; if the Helsinki-Tallinn tunnel is ever built, the terminus is planned in Ülemiste.

https://www.err.ee/1608349781/rail-baltic-kriipsutas-nelja-ulemiste-tunneli-rajamise-projektist-maha