Learn Polish: Najszybsze pociągi nie wożą towaru. - The fastest trains do not transport goods.

wożą comes from wozić, which is the multidirectional or habitual verb for transporting by vehicle. We use it here because the sentence is making a general statement about what fast trains do (or rather, don't do) as a habit. If we were talking about a specific train on a single trip right now, we would use wiozą (from wieźć).

Why is towaru in the Genitive case here? Shouldn't it be Accusative since it's the direct object?

Normally, the direct object is in the Accusative case. However, in Polish, when you negate a verb that takes the Accusative, the object changes to the Genitive case. Because of the word nie, the Accusative towar becomes the Genitive towaru. This rule is called the Genitive of Negation.

The English translation says 'goods' (plural). Is towaru a plural word?

No, towaru is singular here. The base word towar means goods, merchandise, or freight. In Polish, it is often treated as a singular mass noun (just like we say 'merchandise' in English), whereas English uses the plural word 'goods' for this specific translation.

How is the word najszybsze formed?