Na bilheteria, a moça disse que o próximo vagão costuma ficar mais lotado.

Because na is the contraction of em + a.

• em = in / at
• a = the

So:

• em a bilheteria → na bilheteria

This kind of contraction is very common in Portuguese:

• em + o = no
• em + a = na
• em + os = nos
• em + as = nas

Here, na bilheteria means at the ticket office or at the ticket counter, depending on context.

Bilheteria usually means the place where tickets are sold: ticket office, ticket booth, or ticket counter.

It comes from bilhete, which often means ticket or note, depending on context. In this sentence, since we are talking about a train and a vagão, bilheteria is clearly the place where someone buys transit tickets.

Not exactly. Moça can mean young woman, girl, or sometimes just the lady / the woman, depending on context.

In everyday Brazilian Portuguese, a moça is often used for a female worker or attendant in a neutral, polite, conversational way. In this sentence, it probably refers to the woman at the ticket office rather than a literal child or teenager.

So although girl is sometimes possible, young woman or the woman is often better.

Using a moça makes the person sound identifiable in the situation: the woman, meaning the one at the ticket office.

Portuguese often uses definite articles in places where English might not emphasize them as much. Since the listener can infer which woman is being talked about, a moça sounds natural.

Compare:

• Uma moça disse... = A woman said...
  This introduces her as new or unspecified.
• A moça disse... = The woman said...
  This assumes the context makes clear who she is.

Disse is the preterite form of dizer (to say / to tell).

• eu disse = I said
• ela disse = she said

In the sentence, a moça disse means the woman said.

The preterite is used because this was a completed action in the past: she said it at that moment.

Here que means that and introduces reported speech or a reported statement.

So:

• A moça disse que... = The woman said that...

Just like in English, that can sometimes be omitted in translation, but in Portuguese que is very commonly kept.

Examples:

• Ele falou que ia chegar tarde. = He said that he was going to arrive late.
• Ela disse que estava cansada. = She said that she was tired.

O próximo vagão means the next train car or the next carriage.

• próximo = next
• vagão = train car / railcar / carriage

In Brazilian Portuguese, vagão is commonly used for one section/car of a train or subway.

So if someone is talking about where to board, o próximo vagão would be the next car along the train.

Before the noun, próximo usually means next in sequence:

• o próximo vagão = the next car

If you put it after the noun, vagão próximo, it more naturally suggests nearby / close, though that phrasing is less natural in this exact context.

So position matters:

• próximo vagão = next car
• vagão próximo = nearby car / close car

In this sentence, next is clearly the intended meaning.

Costumar + infinitive means to usually, to tend to, or to be in the habit of doing something.

So:

• costuma ficar = usually gets / tends to be / is usually

This adds the idea of a general pattern, not a guaranteed fact.

Compare:

• O próximo vagão fica mais lotado.
  = The next car gets more crowded.
  This sounds more direct, almost like a plain statement of fact.

• O próximo vagão costuma ficar mais lotado.
  = The next car usually gets more crowded / tends to be more crowded.
  This sounds more natural when talking about what generally happens.

Ficar has several meanings, and one very common one is to become, to end up, or to get.

So ficar lotado means to get crowded or to become packed.

That is why:

• costuma ficar mais lotado
  means something like
  usually gets more crowded or tends to be more crowded

Portuguese often uses ficar + adjective for changes of state:

• ficar cansado = get tired
• ficar nervoso = get nervous
• ficar pronto = get ready / become ready
• ficar cheio = get full

Yes, but the meaning would shift a little.

• costuma ficar mais lotado = usually gets / tends to become more crowded
• costuma estar mais lotado = is usually more crowded
• é mais lotado = is more crowded

In real usage, both ficar and estar can work in similar contexts, but ficar often gives a sense of how things end up during the rush or over the course of boarding. It feels dynamic.

So the original sentence sounds very natural for public transit: the next car tends to end up more crowded.

Lotado literally means full, packed, or crowded.

When talking about transportation, rooms, restaurants, etc., it often means:

• crowded
• packed
• full

Examples:

• O ônibus está lotado. = The bus is crowded / packed.
• O show estava lotado. = The concert was full / packed.

In this sentence, mais lotado means more crowded or more packed.

Mais lotado is a comparative: more crowded.

• lotado = crowded / packed
• mais lotado = more crowded

Lotadíssimo is an intensifier meaning something like extremely crowded or super packed, not a comparison.

So:

• mais lotado compares one train car with another
• lotadíssimo just says something is very crowded

Since the sentence compares the next car to another one, mais lotado is the right choice.

It is very common and natural, especially in speech.

You may also hear:

• mais cheio = fuller / more full
• mais movimentado = busier
• mais congestionado = more congested, though this fits traffic more than people inside a car

For trains, buses, and subways, mais lotado is very natural.

Starting with Na bilheteria sets the scene first: At the ticket office...

Portuguese often moves time/place expressions to the front of the sentence for context. It is similar to English sentences like:

• At the station, the clerk said...
• At the ticket office, the woman said...

It is not required, but it is very natural.

The sentence could also be rearranged:

• A moça disse na bilheteria que o próximo vagão costuma ficar mais lotado.

But the original version sounds smoother because it introduces the setting before the action.

It is neutral, everyday Brazilian Portuguese.

Nothing in it is especially slangy or especially formal. It sounds like a normal spoken or written sentence you might hear in a travel situation.

A few features that make it sound natural and conversational:

• a moça instead of a very official term
• costuma ficar to describe a usual pattern
• simple, direct word order

So it is a good example of standard everyday Brazilian Portuguese.