Atentu la trafikon, kiam vi transiras la straton.

The ending -u is the Esperanto verb ending for a command, request, or exhortation. So atentu means something like pay attention or be careful.

This form does not change for singular or plural, because Esperanto uses vi for both you and you all.

The -n shows the direct object. In this sentence, the thing you are being told to pay attention to is la trafiko, so it becomes la trafikon.

A useful point for English speakers: Esperanto atenti normally takes a direct object. English says pay attention to traffic, but Esperanto does not usually need a word corresponding to to here.

Because atenti is usually a transitive verb in Esperanto. That means it directly takes an object.

So the normal pattern is:

• atenti ion = pay attention to something

not usually:

• atenti al io

English often uses a preposition where Esperanto does not, so this is a very common adjustment for learners.

Only the main clause is a command here: Atentu la trafikon.

The clause kiam vi transiras la straton is not a command. It simply tells when the action happens. So it uses the ordinary present-tense form transiras.

In other words:

• atentu = command
• vi transiras = statement about the situation

Esperanto often uses the present tense in time clauses when English might also use the present, as in when you cross the street.

Here the idea is general or habitual: whenever/when you cross the street. It is not pointing to one single specifically future crossing, but giving a general instruction.

So kiam vi transiras la straton is very natural.

Again, the -n marks the direct object. The verb transiri means to cross, and the thing being crossed is the street.

So:

• transiri la straton = cross the street

This is a very common Esperanto pattern: the place or thing crossed is treated as the direct object.

Yes. It is the standard and natural way.

The verb transiri means go across or cross, and it directly takes the thing crossed as its object. So transiri la straton is exactly the structure Esperanto normally uses.

La is the definite article, meaning the.

In this sentence, both nouns are understood as specific in context:

• la trafikon = the traffic around you
• la straton = the street you are crossing

Esperanto often uses la when the situation makes the thing definite and identifiable, even if English might sometimes be a little looser.

Literally, kiam means when. But in a sentence like this, it often has a more general sense, close to whenever.

So the sentence can be understood as a general rule: Pay attention to traffic whenever you cross the street.

That broader meaning comes from the context, not from a different word.

In Esperanto, subordinate clauses are very often separated by commas. The part beginning with kiam is a subordinate time clause, so the comma is normal.

So the structure is:

• main clause: Atentu la trafikon
• subordinate clause: kiam vi transiras la straton

The comma helps show that division clearly.

Yes, absolutely. That version is also correct and natural.

The difference is mainly one of emphasis:

• Atentu la trafikon, kiam vi transiras la straton puts the command first.
• Kiam vi transiras la straton, atentu la trafikon puts the situation first.

Both mean essentially the same thing.

Vi can mean:

• you singular
• you plural
• formal you
• informal you

Esperanto does not normally distinguish those meanings. In this sentence, vi is just a general you, like in English safety instructions.

Yes, Dum vi transiras la straton, atentu la trafikon is also possible.

The difference is small:

• kiam = when
• dum = while / during the time that

In this sentence, kiam is a little more neutral and general. Dum emphasizes the time span of crossing a bit more. Both are understandable and natural.