gyotongsagoga namyeon gyeongcharege baro singohaeya haeyo.

Because 나다 is an intransitive verb, so the accident is treated as the subject, not the object.

• 교통사고가 나다 = a traffic accident occurs / happens
• So 교통사고가 uses the subject particle 가

A very literal breakdown is:

• 교통사고가 = a traffic accident
  • subject marker
• 나면 = if/when it happens

English often says have an accident, but Korean commonly says an accident occurs:

• 사고가 나다 = an accident happens

So 교통사고를 나다 would not be correct here.

Here, 나다 means to occur, to happen, or to break out.

This verb is used in many expressions where something comes up or happens unexpectedly. For example:

• 불이 나다 = a fire breaks out
• 문제가 나다 = a problem occurs
• 사고가 나다 = an accident happens

So in 교통사고가 나면, 나다 does not mean to come out in the physical sense. It means that a traffic accident occurs.

-면 means if or when, depending on context.

In this sentence:

• 교통사고가 나면 = if a traffic accident happens / when a traffic accident happens

Korean often uses -면 in situations where English could use either if or when. Here, both work naturally because the sentence is talking about what you should do in that situation.

Structure:

• 나다 → verb stem 나-
• 나 + 면 → 나면

에게 marks the target/recipient of an action, often translated as to.

So:

• 경찰에게 신고하다 = report to the police

Here, the reporting is directed to the police, so 에게 shows who receives the report.

A note for learners: with organizations like 경찰, Korean also very commonly uses 에:

• 경찰에 신고하다 = also very natural

So 경찰에게 신고하다 is understandable and grammatical, but 경찰에 신고하다 may sound a bit more common in everyday usage.

Korean often leaves out objects when they are already understood from context.

Here, the thing being reported is obviously the traffic accident, so Korean does not need to repeat it.

English usually requires it:

• You must report it to the police immediately.

But Korean can simply say:

• 경찰에게 바로 신고해야 해요
• literally: must report to the police immediately

The omitted object is understood automatically.

바로 here means right away, immediately, or without delay.

So:

• 경찰에게 바로 신고해야 해요 = You must report it to the police immediately

In other contexts, 바로 can also mean things like:

• right/correctly
• just/exactly
• directly

But in this sentence, the time meaning immediately is the important one.

신고해야 해요 expresses obligation: must, have to, or should depending on context.

Breakdown:

• 신고하다 = to report
• 신고해야 = have to report / must report
• 해요 = polite present-style ending

More grammatically:

• -아/어야 하다 = must / have to

So:

• 신고해야 해요 = must report / have to report

In this sentence, must report is the best translation because it sounds like a rule or strong advice.

Because 해요 by itself just means do in a polite way, but 해야 해요 means have to do.

Compare:

• 신고해요 = (I/you/we) report
• 신고해야 해요 = (I/you/we) must report

The -아/어야 하다 pattern adds the meaning of necessity or obligation.

So without -야, the sentence would lose the meaning of must.

Korean often omits the subject when it is obvious from context.

In a sentence like this, the implied subject is usually:

• you
• or people in general

So 교통사고가 나면 경찰에게 바로 신고해야 해요 naturally means:

• If a traffic accident happens, you should/must report it to the police immediately.

Korean does this very often. A full version with the subject included might be:

• 교통사고가 나면 우리는 경찰에게 바로 신고해야 해요
• If a traffic accident happens, we must report it to the police immediately

But normally the subject is left out.

해요 is the polite style, often called the 요-form.

So this sentence is polite and appropriate for:

• general conversation
• instructions
• everyday announcements
• speaking politely to someone

Compare levels:

• 신고해야 해 = casual
• 신고해야 해요 = polite
• 신고해야 합니다 = more formal

So the original sentence sounds polite but not overly stiff.

Yes. -면 can often be understood as either if or when.

So this sentence can be read as:

• If a traffic accident happens, you must report it to the police immediately
• When a traffic accident happens, you must report it to the police immediately

The difference depends on how the speaker is framing the situation:

• if = talking about a possible situation
• when = talking more generally about what to do in that situation

Both are natural translations here.

The sentence follows typical Korean word order, where the verb comes at the end.

Breakdown:

• 교통사고가 = a traffic accident
• 나면 = if/when it happens
• 경찰에게 = to the police
• 바로 = immediately
• 신고해야 해요 = must report

A very literal order would be:

• Traffic accident if-happens, to-the-police immediately report-must

Natural English reorders this as:

• If a traffic accident happens, you must report it to the police immediately.

So this sentence is a good example of how Korean often puts the main action at the end.

You might be understood, but 교통사고가 나다 is the standard, natural expression for a traffic accident happens.

• 사고가 나다 = the normal collocation
• 사고가 생기다 = less natural in this context

Korean often uses fixed verb pairings, and this is one of them. So it is best to memorize:

• 교통사고가 나다
• 사고가 나다

rather than trying to build it from a more general verb like 생기다.

It can feel like either strong advice or a rule/obligation, depending on context, but the grammar strongly suggests obligation.

Because of -아/어야 하다, the sentence means:

• you must report it
• you have to report it

So if this appears in a safety lesson, public notice, or legal explanation, it sounds like a rule. In ordinary conversation, it can also sound like strong advice.

So the nuance is stronger than just:

• 신고하는 게 좋아요 = it’s good to report it

Instead, it says:

• 신고해야 해요 = you have to report it