Αν δεν είχα βάλει ζώνη, θα είχα φοβηθεί περισσότερο όταν πάτησα απότομα φρένο.

This is the Greek way to express a past unreal condition:
If I hadn’t ..., I would have ...

The pattern here is:

• Αν + past perfect in the if-clause
• θα + past perfect in the result clause

So:

• Αν δεν είχα βάλει ζώνη = If I hadn’t put on a seat belt / If I hadn’t been wearing a seat belt
• θα είχα φοβηθεί περισσότερο = I would have been more frightened

A very important point for English speakers:

• Greek does not use θα in the αν-clause
• So Αν δεν θα είχα βάλει... would be wrong here

This is one of the standard ways to form the equivalent of the English third conditional.

Είχα βάλει is the past perfect of βάζω.

• βάζω = I put / I put on
• έβαλα = I put
• έχω βάλει = I have put
• είχα βάλει = I had put

In this sentence, είχα βάλει ζώνη means:

• literally: I had put on a seat belt
• more naturally in English: I had been wearing a seat belt

Greek often uses βάζω for clothing or things you put on your body, including a seat belt.

Because Greek commonly expresses this idea with the verb βάζω (put on).

So:

• βάζω ζώνη = I put on / wear a seat belt
• φόρεσα ζώνη may also be heard, but βάζω ζώνη is extremely natural and common

This is one of those places where Greek and English choose different everyday verbs:

• English: wear a seat belt
• Greek: put on a seat belt

Even if the English translation uses wear, the Greek phrasing is perfectly normal.

In Greek, some everyday expressions often omit the article, especially in fixed or common collocations.

So both of these can be natural depending on context:

• έβαλα ζώνη
• έβαλα τη ζώνη

But they do not feel exactly the same in every context.

Here:

• ζώνη without an article sounds general and idiomatic, like wear a seat belt
• τη ζώνη could sound more like a specific belt that is understood in the situation

Since seat belt language is often formulaic, βάζω ζώνη is very common.

Θα είχα φοβηθεί points to a completed reaction in the past:
I would have gotten more scared / I would have been more frightened

The verb is φοβάμαι, but its aorist/perfect system looks different:

• φοβάμαι = I am afraid / I fear
• φοβήθηκα = I got scared / I was frightened
• έχω φοβηθεί = I have gotten scared / I have been frightened
• θα είχα φοβηθεί = I would have gotten more scared / would have been more frightened

If you said θα φοβόμουν, that would usually sound more like:

• I would be afraid
• or a more repeated/ongoing kind of feeling in the past, depending on context

Here the speaker is talking about a specific past moment and the reaction to it, so θα είχα φοβηθεί fits very well.

Because πάτησα presents the action as a single, complete event:

• πάτησα φρένο = I hit the brake / I slammed on the brakes

That matches the context very well: it was one sudden action.

By contrast:

• πατούσα would suggest something more ongoing, repeated, or descriptive
• it would not fit as naturally with a sudden one-time event

So:

• όταν πάτησα απότομα φρένο = when I suddenly hit the brakes

The aorist is the normal choice for a single event in the past.

Because όταν πάτησα απότομα φρένο refers to the actual past event that happened.

The logic of the sentence is:

• I did suddenly hit the brakes
• I did feel fear
• but if I had not been wearing a seat belt, I would have felt even more fear

So the braking event is treated as a real past occurrence, not as something unreal. That is why simple past (πάτησα) is natural.

In other words:

• the if-clause is hypothetical/counterfactual
• the when-clause refers to the real moment being discussed

Απότομα is an adverb meaning:

• suddenly
• abruptly
• sharply

Here it modifies πάτησα φρένο, so the idea is:

• I braked suddenly
• I hit the brakes sharply
• I slammed on the brakes

It describes the manner of braking.

This is a very common idiomatic expression.

• πατάω φρένο literally = I press brake
• naturally = I brake / I hit the brakes

Even though English often says the brakes in the plural, Greek very often uses singular φρένο in this expression.

So a learner should think of πατάω φρένο as a chunk meaning:

• brake
• hit the brakes
• slam on the brakes

It is much more idiomatic than translating word by word.

Both can be possible in many contexts, but περισσότερο is very natural and standard here.

• περισσότερο = more
• πιο πολύ = also more, often a bit more conversational depending on context

In this sentence, θα είχα φοβηθεί περισσότερο means:

• I would have been more frightened
• I would have gotten even more scared

So περισσότερο is simply the adverbial comparative of much/more here.

The word order is natural, but Greek has some flexibility.

The sentence begins with the condition:

• Αν δεν είχα βάλει ζώνη, ...

That is very common, just like English often starts with If...

Then comes the result:

• θα είχα φοβηθεί περισσότερο ...

And then the time clause:

• όταν πάτησα απότομα φρένο

This order makes the logic very clear:

1. hypothetical condition
2. hypothetical result
3. real moment being referred to

You could sometimes rearrange parts of the sentence in Greek, but the given order is smooth and easy to follow.

Yes, ζώνη by itself can mean belt in general. But in this context, it is clearly understood as seat belt.

Why?

Because of the surrounding words:

• Αν δεν είχα βάλει ζώνη
• όταν πάτησα απότομα φρένο

The mention of suddenly braking makes the meaning seat belt obvious.

In everyday Greek, people often just say ζώνη when the situation already makes it clear they mean seat belt.