Se não usares os piscas, os outros condutores não adivinham para onde vais.

Because after se meaning if, Portuguese often uses the future subjunctive when talking about a possible future situation:

• Se não usares... = If you don’t use...

This is very common in European Portuguese for real future conditions.

A quick comparison:

• Se estudas, aprendes. = If you study, you learn.
  This sounds more like a general truth.
• Se estudares, passas. = If you study, you’ll pass.
  This refers to a future possibility.

So in your sentence, usares fits because it means if you don’t use them in a future or situational sense.

Here, no. In this sentence, usares is the future subjunctive of usar for tu.

However, it looks exactly the same as the personal infinitive form for tu:

• para usares = for you to use → personal infinitive
• se usares = if you use → future subjunctive

So the form is the same, but the grammar is different. You tell them apart by the structure:

• after se → usually future subjunctive
• after para → often personal infinitive

Because Portuguese often drops subject pronouns when the verb form already makes the subject clear.

In this sentence:

• usares clearly shows tu
• vais also clearly shows tu

So tu is understood:

• Se não usares os piscas... = If you don’t use your indicators...
• ...para onde vais. = ...where you are going.

European Portuguese especially tends to omit subject pronouns unless they are needed for emphasis or contrast.

Os piscas means the indicators / turn signals / blinkers on a vehicle.

In Portugal, pisca is a very common everyday word for a turn signal. It comes from the idea of something that blinks.

Related terms:

• pisca = indicator, turn signal
• pisca-pisca = blinking light, also used informally
• indicador de mudança de direção = more formal/technical term

So usar os piscas means to use your turn signals / indicators.

Because Portuguese often refers to them as a pair or as the signaling system in general:

• usar os piscas = use your indicators

This is similar to English, where people often say use your indicators rather than use your indicator.

Even if only one side flashes at a time, the plural is very natural because the car has left and right indicators, and the phrase refers to the system as a whole.

Yes, it is especially common in Portugal.

A learner who knows Brazilian Portuguese might expect something else, especially:

• seta in Brazil = turn signal / indicator

Also:

• Portugal: condutor
• Brazil: motorista is more common for driver

So this sentence sounds clearly European Portuguese in vocabulary and style.

Because os outros condutores means the other drivers — the specific other drivers around you, such as the ones on the road with you.

• os outros condutores = the other drivers
• outros condutores = other drivers, more general

The definite article os makes it sound more specific and natural in this context.

In European Portuguese, condutor is the normal general word for driver.

• condutor = driver
• motorista in Portugal often sounds more like a professional driver, chauffeur, bus driver, etc.

In Brazilian Portuguese, motorista is the everyday word for driver, but in Portugal condutor is usually the better choice for ordinary road-use contexts.

Because Portuguese often uses the simple verb adivinhar directly, where English might prefer something like can’t guess or can’t know.

So:

• os outros condutores não adivinham literally = the other drivers do not guess
• but in natural English it often means the other drivers can’t tell / can’t guess / can’t know

The idea is that other drivers are not mind readers. Portuguese does not always need to add podem or conseguem for that meaning.

Literally, adivinhar means to guess.

In this sentence, it means something like:

• guess
• figure out
• tell
• know without being told

So the sense is:

• If you don’t use your indicators, the other drivers can’t guess where you’re going.

It is slightly stronger than just know. It suggests that without a signal, they would have to guess your intention.

Because this is about destination — where you are going to — not just location.

• onde = where
• para onde = to where / where to

Since the verb is ir para in this idea of direction, para onde is the natural choice:

• para onde vais = where you’re going

If you said just onde vais, some speakers might still understand it, but para onde is clearer and more standard for movement toward a destination.

Because vais is the present indicative, and that is what Portuguese uses here.

This part:

• para onde vais = where you are going

is an indirect question, not a wish, doubt, or command, so there is no need for the subjunctive.

• vais = indicative
• vás = subjunctive

You would use vás in sentences like:

• Espero que vás com cuidado. = I hope you go carefully.

But here it is simply stating the destination that others cannot figure out:

• não adivinham para onde vais

Because Portuguese, like English, often uses the present tense for:

• general truths
• habits
• warnings
• likely future situations

This sentence is basically a general rule:

• If you don’t use your indicators, other drivers can’t guess where you’re going.

So the present tense makes perfect sense. It gives the sentence a general, practical, rule-like meaning.

Yes, absolutely.

A very literal translation is:

• If you don’t use the indicators, the other drivers don’t guess where you’re going.

But more natural English would usually be:

• If you don’t signal, other drivers can’t tell where you’re going.
• If you don’t use your turn signals, other drivers can’t guess where you’re going.

So the Portuguese is straightforward, but the best English translation may be a little less literal.

Yes. It sounds natural in European Portuguese.

A few things make it feel very Portuguese from Portugal:

• usares with implied tu
• os piscas
• condutores

It is the kind of sentence you might hear in driving advice, road safety discussions, or everyday criticism of bad driving.