chaseoneul bakkugi jeone banghyangjisideungeul kyeopnida.

차선 means lane (as in a traffic lane).

The -을 is the object marker, so 차선을 means the lane as the thing being acted on.

In this sentence:

• 차선 = lane
• 차선을 바꾸다 = to change lanes / to change the lane

Even though English says change lanes, Korean often treats lane as the direct object:

• 차선을 바꾸다 = literally change the lane

Because 차선 ends in a consonant, it takes -을 rather than -를.

In Korean, when a verb comes before 전에 (before), it usually has to be turned into a noun-like form. That is what -기 does.

So:

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

You generally cannot say 바꾸다 전에 here.

A useful pattern is:

• Verb stem + 기 전에 = before doing something

Examples:

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

전에 means before.

In this sentence, it marks that one action happens earlier than another:

• 차선을 바꾸기 전에 = before changing lanes
• 방향지시등을 켭니다 = turn on the turn signal

So the order is:

1. turn on the signal
2. then change lanes

You may also see 전 without 에 in some contexts, but 전에 is very common and natural in this pattern.

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

It breaks down roughly like this:

• 방향 = direction
• 지시 = indication
• 등 = light

So it is literally something like direction-indicating light.

In everyday speech, many Koreans also say:

• 깜빡이

That is a much more casual, spoken word for turn signal/blinker.

So:

• 방향지시등 = formal, official, textbook, driving-related language
• 깜빡이 = casual everyday speech

켜다 means to turn on something like a light, machine, or device.

Since a turn signal is a light, Korean uses 켜다 naturally:

• 방향지시등을 켜다 = to turn on the turn signal

In this sentence:

• 켭니다 is the formal polite present form of 켜다

Conjugation:

• dictionary form: 켜다
• formal polite: 켭니다

This form is very common in instructions, rules, manuals, and driving guidance.

Yes, 켭니다 is grammatically present tense in the formal polite style.

But in Korean, this form is often used not only for plain statements, but also for:

• instructions
• rules
• announcements
• manual-style directions

So 방향지시등을 켭니다 can sound like:

• You turn on the turn signal
• Turn on the turn signal
• One should turn on the turn signal

The exact English wording depends on context. In driving instructions, it is naturally understood as an instruction or guideline.

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

In a sentence like this, the listener already understands that the instruction is aimed at the driver, so there is no need to say you explicitly.

If you added a subject, it might sound unnecessary unless you were emphasizing it.

So this is normal:

• 차선을 바꾸기 전에 방향지시등을 켭니다.

The implied subject is something like:

• you
• the driver
• one

Korean relies heavily on context for this.

Korean word order is generally Subject-Object-Verb, and important time or condition phrases often come before the main action.

So this sentence is structured like:

• 차선을 바꾸기 전에 = before changing lanes
• 방향지시등을 = the turn signal
• 켭니다 = turn on

Literally, it is closer to:

• Before changing lanes, turn on the turn signal.

This is very normal Korean structure: background information first, main verb at the end.

For changing lanes, 바꾸다 is the natural verb.

• 차선을 바꾸다 = to change lanes

Other verbs would usually not fit:

• 갈아타다 means something like transfer or change to another vehicle (for example, changing trains or buses), so it is not used for traffic lanes.
• 변경하다 means to change/modify and is more formal or bureaucratic. It can appear in very official writing, but 차선을 바꾸다 is much more natural in everyday Korean.

So for learners, 차선을 바꾸다 is the best expression to remember.

Because the turn signal is the direct object of 켜다 (to turn on).

So:

• 방향지시등을 켭니다 = turn on the turn signal

If you used 은/는, it would mark the noun as a topic or contrast:

• 방향지시등은 켭니다 could sound like as for the turn signal, (I/you) turn it on or imply contrast with something else.

That is possible in the right context, but the neutral, standard sentence uses -을.

A rough pronunciation guide is:

• 바꾸기 ≈ bak-ku-gi
• 전에 ≈ jeo-ne

So together:

• 바꾸기 전에 ≈ bak-ku-gi jeo-ne

The ㄲ in 바꾸기 is a tense consonant, so it is stronger and tighter than a regular ㄱ sound. It is not exactly like English, but it should sound firmer than 가.

Also:

• 전 is pronounced with the vowel ㅓ, which is like uh in many learning guides, not o.

Yes, this sentence is in the formal polite style:

• 켭니다

This style is common in:

• instructions
• announcements
• textbooks
• driving rules
• public information

More casual versions could be:

• 차선을 바꾸기 전에 방향지시등을 켜요.
  Polite everyday style

• 차선 바꾸기 전에 깜빡이 켜.
  Casual speech

Notice that in casual speech:

• 방향지시등 may become 깜빡이
• particles may sometimes be dropped in conversation
• the verb ending becomes less formal

Yes. In practice, 차선을 바꾸다 is understood as to change lanes.

Even though 차선 is singular in form, Korean often does not mark singular/plural the way English does. So depending on context, it can correspond to:

• change the lane
• change lanes
• switch to another lane

In a driving context, English naturally translates it as before changing lanes.

So you do not need to worry about adding a plural marker here.