Na ulazu na autocestu platili smo cestarinu, a rampa se otvorila tek nakon nekoliko sekundi.

Because the two na phrases do two different jobs:

• na ulazu = at the entrance
• na autocestu = onto the motorway

So the sentence is literally structured like:

• at the entrance
• onto the motorway

In English we would usually say at the entrance to the motorway, but Croatian often uses na in both places here.

Because Croatian changes case depending on meaning, and na can take different cases.

1. na + locative = location, no movement

   • na ulazu = at the entrance
   • ulazu is locative singular of ulaz

2. na + accusative = motion toward something

   • na autocestu = onto the motorway
   • autocestu is accusative singular of autocesta

So:

• na ulazu answers where?
• na autocestu answers onto what?/to where?

This is a very common Croatian pattern.

Platili smo means we paid.

It is the Croatian perfect tense, made with:

• the past active participle: platili
• the auxiliary to be: smo = we are/have in this tense structure

So literally, it is something like paid we-have, but in natural English: we paid.

Why is smo after the participle?
In Croatian, short unstressed words called clitics often come in the second position of the clause. So Croatian word order is more flexible than English.

You can think of:

• Platili smo cestarinu = normal and natural
• Mi smo platili cestarinu = also possible, with mi adding emphasis

Because it is the direct object of platili smo.

• dictionary form: cestarina = toll
• accusative singular: cestarinu

Since they paid the toll, Croatian uses the accusative:

• platiti što? → cestarinu

This is very common with feminine nouns ending in -a:

• knjiga → knjigu
• kava → kavu
• cestarina → cestarinu

Here a means something like and, but with a slight sense of contrast or shift.

The sentence has two parts:

• platili smo cestarinu
• a rampa se otvorila tek nakon nekoliko sekundi

So a links them, but it also suggests a change in focus:

• we paid the toll, and then / but
• the barrier opened only after a few seconds

It is not as strongly contrastive as ali (but), but it is not exactly the same as simple i (and) either.

A good feel for a here is:

• and
• while
• but then

depending on context.

Se here makes the verb mean opened in the sense of opened by itself / became open, rather than someone actively opening it.

• otvoriti = to open
• otvoriti nešto = to open something
• otvoriti se = to open / to become open

So:

• Otvorili su rampu. = They opened the barrier.
• Rampa se otvorila. = The barrier opened.

In English, we often do not mark this difference clearly, but Croatian often uses se for this kind of intransitive or middle meaning.

Because the verb agrees with rampa, and rampa is a feminine singular noun.

So the past participle must also be feminine singular:

• rampa → otvorila se

Compare:

• prozor se otvorio = the window opened
  (prozor is masculine)
• vrata su se otvorila = the door / doors opened
  (vrata is plural in form)

Agreement in Croatian past tense is very important.

Tek adds the meaning of only, not until, or only then.

So:

• nakon nekoliko sekundi = after a few seconds
• tek nakon nekoliko sekundi = only after a few seconds

It suggests delay. The speaker is implying that the barrier did not open immediately.

So tek gives the sentence a nuance like:

• only after several seconds
• not until several seconds later

Because nakon requires the genitive case, and nekoliko is also followed by genitive.

Break it down:

• nakon = after
• nekoliko = several / a few
• sekundi = genitive plural of sekunda

So:

• nakon nekoliko sekundi = after several seconds

This is a useful pattern to remember:

• nakon jednog dana = after one day
• nakon nekoliko minuta = after a few minutes
• nakon nekoliko sekundi = after a few seconds

Because Croatian does not have articles like a and the.

So Croatian simply says:

• rampa
• ulaz
• cestarina

and the listener understands from context whether the meaning is:

• a barrier or the barrier
• an entrance or the entrance
• a toll or the toll

In this sentence, English naturally uses the because the objects are specific in context:

• the entrance
• the toll
• the barrier

But Croatian does not need an article to show that.

Both platili smo and se otvorila are in the Croatian perfect tense, which is the most common way to talk about past events in everyday language.

Forms:

• platili smo = we paid
• se otvorila = it opened

The Croatian perfect is formed with:

• a past participle
• a present-tense form of biti (to be) as auxiliary

Examples:

• radio sam = I worked
• došla je = she came
• platili smo = we paid

In everyday Croatian, this tense often covers what English might express as simple past.

Yes, both are perfective here, and that matters.

• platiti is perfective: to pay as a completed action
• otvoriti se is perfective: to open as a completed event

That fits the sentence because both actions are seen as finished, whole events:

• they paid the toll
• the barrier opened

If you used imperfective verbs, the meaning would shift toward process, repetition, or ongoing action.

For example:

• plaćali smo would suggest repeated or ongoing paying
• otvarala se would suggest repeated opening or an unfolding process in the right context

So the perfective forms are exactly what you would expect in a sentence describing completed events in sequence.

Yes, Croatian word order is flexible, though some versions sound more natural than others.

The original sentence is very natural:

• Na ulazu na autocestu platili smo cestarinu, a rampa se otvorila tek nakon nekoliko sekundi.

But you could also hear things like:

• Cestarinu smo platili na ulazu na autocestu, a rampa se otvorila tek nakon nekoliko sekundi.
• Na ulazu na autocestu smo platili cestarinu...

The meaning stays basically the same, but the focus changes slightly.

Croatian often moves words around for:

• emphasis
• rhythm
• topic vs. new information

Still, the original version is a very good neutral model for learners.