Learn Finnish: Raitiotietä ei jatkettane etelään. - The tramway is unlikely to be extended to the south.

First, find the present passive form: jatketaan (it is extended). Drop the -aan and add the passive potential marker -aneen to get the affirmative jatkettaneen (it is probably extended). For the negative, use ei and remove the personal ending -en, leaving you with ei jatkettane.

Why is the object Raitiotietä in the partitive case here?

Because this is a negative sentence. The object of any negative action in Finnish must be in the partitive case. If this sentence were affirmative, the object of the passive verb would be in the nominative case: Raitiotie jatkettaneen.

Why does the compass direction etelä take the illative ending -än rather than the allative -lle?

In Finnish, compass points typically use the inner location cases (inessive, elative, illative) rather than the outer ones. When expressing movement towards a compass direction, you use the illative case, so etelä becomes etelään.

Can jatkaa mean both 'to continue' and 'to extend'?

Yes. While jatkaa frequently translates to continuing an action, when talking about physical lines or structures like a road, a deadline, or a tramway, it means to extend or lengthen it.