Antes da ultrapassagem, é importante usar os piscas e olhar para o retrovisor.

Because da is the contraction of de + a.

After antes, Portuguese normally uses de, and when the next noun has the definite article a, they contract:

• antes de + a ultrapassagem → antes da ultrapassagem

So antes da ultrapassagem means before the overtaking manoeuvre.

Antes de ultrapassagem sounds incomplete and unnatural here. If you do not want to use the noun ultrapassagem, the natural alternative is:

• Antes de ultrapassar... = Before overtaking...

Ultrapassagem is the noun form of ultrapassar.

In driving context, it means overtaking or passing another vehicle. It is the manoeuvre itself, not just the idea of going faster.

So:

• ultrapassar = to overtake
• ultrapassagem = overtaking, the overtaking manoeuvre

This is a very common word in road-safety language and driving rules in Portugal.

Yes, absolutely. Both are correct.

• Antes da ultrapassagem, é importante...
• Antes de ultrapassar, é importante...

The difference is mainly one of structure:

• antes da ultrapassagem uses a noun
• antes de ultrapassar uses a verb

For many learners, antes de ultrapassar feels more direct because it matches English more closely: before overtaking.

Because after é importante, Portuguese normally uses the infinitive directly, without de.

So you say:

• É importante usar os piscas
• É importante olhar para o retrovisor

Not:

• É importante de usar
• É importante de olhar

This is a common pattern in Portuguese:

• É bom descansar
• É necessário estudar
• É importante verificar

So the structure is:

• é + adjective + infinitive

In European Portuguese, os piscas means the indicators / turn signals / blinkers on a vehicle.

The singular is pisca, but in practice the plural piscas is very common because cars have signal lights on both sides.

Examples:

• Liga o pisca = Turn on the indicator
• Usa os piscas = Use your indicators

This is very natural in Portugal.

A useful note: in Brazilian Portuguese, people often say seta instead.

Yes, usar os piscas is natural and correct.

In driving contexts, you may also hear:

• ligar os piscas = to switch on the indicators
• fazer sinal = to signal
• dar o pisca = to indicate, to put the blinker on

So usar os piscas is a general and perfectly acceptable way to say that you should use them properly before overtaking.

Because the verb olhar normally uses para when you say what you are looking at.

So:

• olhar para o retrovisor = to look at the mirror

This is different from English, where look can go directly before the object in some expressions.

In Portuguese, the normal pattern is:

• olhar para alguém
• olhar para alguma coisa

Examples:

• Olha para a estrada
• Olha para o lado
• Olha para o espelho

The singular is possible because it refers to the mirror in a general or relevant sense, often the rear-view mirror.

But in real driving instructions, you may also hear the plural:

• olhar para os retrovisores

That can sound even more practical, since drivers often check more than one mirror.

So:

• o retrovisor = the mirror / the rear-view mirror
• os retrovisores = the mirrors

The singular in your sentence is not wrong at all; it is just slightly more general or simplified.

Both exist.

• retrovisor is very common on its own
• espelho retrovisor is the fuller expression

In everyday Portuguese, especially in driving contexts, people often just say retrovisor because the meaning is obvious.

So:

• olhar para o retrovisor is completely normal
• olhar para o espelho retrovisor is also correct, but a bit more explicit

Because this is an impersonal structure.

Portuguese often uses é importante + infinitive to give general advice without naming a specific person:

• É importante estudar
• É importante descansar
• É importante usar os piscas

It works like English It is important to...

So the sentence means something general, like a rule or recommendation for anyone driving. There is no need to say você or tu.

The comma separates the introductory phrase from the main clause.

• Antes da ultrapassagem = introductory time expression
• é importante usar os piscas e olhar para o retrovisor = main statement

This comma is very natural in writing and helps readability. You may sometimes see short introductory phrases without a comma in informal writing, but here the comma is standard and clear.

Yes.

The sentence has two infinitives coordinated by e:

• usar os piscas
• olhar para o retrovisor

Both depend on é importante. In other words:

• It is important to use the indicators
• and to look at the mirror

Portuguese often avoids repeating the structure when two infinitives share the same idea:

• É importante usar os piscas e olhar para o retrovisor instead of
• É importante usar os piscas e é importante olhar para o retrovisor

Both are grammatical, but the first is much more natural.