chaseoneul bakkugi jeone banghyangjisideungeul kyeoyaman hapnida.

A natural breakdown is:

• 차선을 = 차선 (lane) + -을/를 (object marker)
• 바꾸기 전에 = before changing
• 방향지시등을 = turn signal/indicator + -을/를 (object marker)
• 켜야만 합니다 = must turn on

So the structure is basically:

[Before changing lanes] [the turn signal] [must be turned on].

Korean often puts the time/condition part first and the main action last.

Because there are really two verbs in the sentence:

1. 차선을 바꾸다 = to change lanes
2. 방향지시등을 켜다 = to turn on the turn signal

So each verb has its own object:

• 차선을 belongs to 바꾸기 전에
• 방향지시등을 belongs to 켜야만 합니다

This is very normal in Korean when one clause is embedded inside another.

Because 전에 usually attaches to a noun-like form, and -기 turns a verb into a noun-like expression.

• 바꾸다 = to change
• 바꾸기 = changing / the act of changing
• 바꾸기 전에 = before changing

This -기 전에 pattern is very common:

• 먹기 전에 = before eating
• 자기 전에 = before sleeping
• 출발하기 전에 = before departing

So 바꾸다 전에 is not the normal form here.

전에 means before.

In this sentence, 차선을 바꾸기 전에 means before changing lanes or before you change lanes.

It tells you that the action of turning on the signal should happen earlier than the lane change.

방향지시등 is the formal word for a turn signal / indicator.

It is understandable and correct, but in everyday conversation many Koreans often say:

• 깜빡이 = blinker / turn signal

So in casual speech, people might say:

• 차선 바꾸기 전에 깜빡이 켜야 해요.

That sounds more conversational.

Because 켜다 means to turn on something like a light, device, or electrical function.

Common examples:

• 불을 켜다 = turn on the light
• 에어컨을 켜다 = turn on the air conditioner
• 방향지시등을 켜다 = turn on the turn signal

Since a turn signal is treated like something you activate electrically, 켜다 is the natural verb.

It breaks down like this:

• 켜다 = to turn on
• 켜야 하다 = have to turn on / must turn on
• 켜야만 하다 = must turn on, with extra emphasis
• 켜야만 합니다 = formal/polite style

So -아/어야 하다 expresses obligation, and -아/어야만 하다 makes that obligation sound stronger.

This sentence has the feeling of a rule, instruction, or safety requirement.

Not in the simple literal sense of only.

In many situations, 만 does mean only, but in the pattern -아/어야만 하다, it works more as an emphatic marker. It strengthens the idea of necessity.

So:

• 켜야 합니다 = you have to turn it on
• 켜야만 합니다 = you absolutely must turn it on

The second one sounds stronger and more forceful.

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

Here, the implied subject is something like:

• you
• the driver
• one

So the sentence does not need to say 당신은 or 운전자는 unless the speaker wants to emphasize it.

That is completely normal Korean.

Because Korean very often puts time, condition, or background information before the main clause.

So this order is very natural:

• 차선을 바꾸기 전에 = before changing lanes
• 방향지시등을 켜야만 합니다 = you must turn on the signal

In English, this is also possible: Before changing lanes, you must turn on your signal.

Korean strongly prefers this kind of setup, where the context comes first and the main statement comes later.

This sentence is formal and polite, especially because of 합니다. It sounds like something you might see in:

• a driving manual
• a test question
• a public safety notice
• an instructional explanation

More casual versions could be:

• 차선을 바꾸기 전에 방향지시등을 켜야 해요.
• 차선 바꾸기 전에 깜빡이 켜야 해요.

The meaning stays the same, but the tone becomes more conversational.