Upgrading is magnitudes faster than building new. Apparently the current Finnisch idea is to actually build new tracks next to the old one, which requires wider

Upgrading is magnitudes faster than building new. Apparently the current Finnisch idea is to actually build new tracks next to the old one, which requires wider beds, which requires more land, which requires more negotiations. Replacing in situ would be faster, but you would cripple your whole network for the duration. It's a tradeoff and worthy of deliberation.