Learn Hardcore Croatian: Vlak vozi prebrzo kroz grad. - The train goes too fast through the city.

Vlak means train.
It is a masculine noun in Croatian.
In the nominative singular (the dictionary form), it is simply vlak.
You can tell it’s masculine because it usually takes masculine endings and masculine adjectives: e.g. brzi vlak = fast train.

What exactly does vozi mean here, and what is its infinitive form?

Vozi comes from the verb voziti, which literally means to drive / to transport / to carry (by vehicle).
In this sentence, vlak vozi is best translated as the train is going / runs / travels, even though the literal sense is “drives”.
Vozi is the 3rd person singular, present tense form:

ja vozim
ti voziš
on/ona/ono vozi
mi vozimo
vi vozite
oni/one/ona voze

Why is vozi used instead of a verb that literally means “to go” like ići?

In Croatian, voziti is often used for vehicles (trains, buses, cars) in the sense of to run / to operate / to travel.
While ići means to go, it’s more general and often used for people going somewhere.
Saying vlak ide prebrzo is understandable, but vlak vozi prebrzo is more natural, because trains are typically said to voze (they “drive/run”) along tracks.

What does prebrzo mean exactly, and how is it formed?

Prebrzo means too fast / excessively fast.
It is an adverb, formed from the adjective brz (fast).
The prefix pre- often has the meaning too / overly / excessively, so:

brzo = fast / quickly
prebrzo = too fast / too quickly

What is the difference between brzo and prebrzo?

brzo = fast, quickly (neutral, just says the speed is high)
prebrzo = too fast, excessively fast (adds a negative or critical nuance)

So:

Vlak vozi brzo kroz grad. = The train goes fast through the city.
Vlak vozi prebrzo kroz grad. = The train goes too fast through the city.

Is prebrzo an adjective or an adverb here, and what does it modify?

In this sentence, prebrzo is an adverb.
It modifies the verb vozi (how the train is going).
If you wanted an adjective describing the train itself, you’d use prebrz:

prebrz vlak = a too-fast train (adjective)
vlak vozi prebrzo = the train goes too fast (adverb)

What does the preposition kroz mean, and what case does it require?

Kroz means through.
It always takes the accusative case.
Here, grad is in the accusative singular: kroz grad = through the city.
You’ll see the same pattern with other nouns: kroz šumu (through the forest), kroz tunel (through the tunnel), etc.

Why is it kroz grad and not something like kroz grada?

The noun grad (city/town) is a regular masculine noun.
Its accusative singular form is the same as the nominative: grad.
So:

Nominative: grad (subject)
Accusative: grad (object, used after kroz)

Grada would be genitive singular, used for “of the city” (e.g. centar grada = the center of the city), not after kroz.

What does grad mean exactly? Is it “city” or “town”?

Grad generally means city, but it can also be used for town, depending on size and context.
Croatian doesn’t always distinguish strictly between city and town the way English sometimes does.
In this sentence, kroz grad can naturally be translated as through the city or through town, depending on what sounds more natural in English.

Why doesn’t Croatian use an article like “the” before vlak or grad?

Croatian has no articles (no equivalents of “a/an” or “the”).
Definiteness or indefiniteness is understood from context, word order, or extra words, not from articles.
So vlak can mean a train or the train, and grad can mean a city / town or the city / town, depending on context.
In English, we add the to make the sentence sound natural: The train goes too fast through the city.

Is the word order Vlak vozi prebrzo kroz grad fixed, or can it change?

The given word order is natural and neutral: Subject – Verb – Adverb – Prepositional phrase.
However, Croatian allows some flexibility for emphasis. For example:

Vlak prebrzo vozi kroz grad. (emphasis on “too fast”)
Prebrzo vlak vozi kroz grad. (stronger emphasis on “too fast”, a bit more stylistic)

But the original Vlak vozi prebrzo kroz grad. is the most straightforward, neutral version.

Can you omit vlak and just say Vozi prebrzo kroz grad?

Yes, you can omit the subject when it’s clear from context, because the verb ending already shows person and number.
If it’s obvious you’re talking about the train, Vozi prebrzo kroz grad. would mean It goes too fast through the city.
However, if there was no prior context, including Vlak makes the sentence clearer.

What is the basic word-for-word breakdown of the sentence?

Vlak – train (subject, nominative singular, masculine)
vozi – goes / drives / runs (3rd person singular, present, from voziti)
prebrzo – too fast / too quickly (adverb from brz, with prefix pre-)
kroz – through (preposition, governs accusative)
grad – city / town (object of the preposition, accusative singular, masculine)

Altogether: Vlak vozi prebrzo kroz grad. = The train goes too fast through the city.

How would you say “The train goes fast through the city” without the “too”?

You simply drop the prefix pre- from prebrzo:

Vlak vozi brzo kroz grad. = The train goes fast through the city.
Brzo is the neutral adverb “fast / quickly”, without the meaning of “too”.