Quando piove, bisogna rallentare e non accelerare troppo.

Because piove is an impersonal verb. In Italian, weather verbs like piove, nevica, and grandina usually appear without a subject pronoun.

So:

• Piove = It’s raining / It rains
• not esso piove or anything similar

English needs the dummy subject it, but Italian does not.

Quando means when or whenever, while se means if.

In this sentence, Quando piove gives a general rule:

• Quando piove, bisogna rallentare... = Whenever it rains, you need to slow down...

If you said Se piove, that would sound more like a specific condition:

• Se piove, restiamo a casa. = If it rains, we’ll stay home.

So quando works well here because the sentence is giving general advice for rainy conditions.

Bisogna means something like:

• it is necessary
• one must
• you have to

It comes from the verb bisognare, which is often used impersonally.

So:

• Bisogna rallentare = You have to slow down / One must slow down

It is a very common way in Italian to express a general necessity without naming a specific person.

Because bisogna is general and impersonal.

Compare:

• Bisogna rallentare = One must slow down / You have to slow down in general
• Devi rallentare = You must slow down addressed directly to one person
• Dovresti rallentare = You should slow down, which sounds softer

In your sentence, the speaker is giving a general rule about driving in the rain, not talking to one specific person, so bisogna is the most natural choice.

Because after bisogna, Italian normally uses an infinitive to express the action that is necessary.

Structure:

• bisogna + infinitive

Examples:

• Bisogna studiare. = You have to study.
• Bisogna aspettare. = You have to wait.
• Bisogna rallentare. = You have to slow down.

So rallentare and accelerare stay in their basic dictionary form.

In Italian, non normally goes before the verb it negates.

So:

• non accelerare = not to accelerate
• non parlare = not to speak
• non correre = not to run

In this sentence:

• rallentare e non accelerare troppo

means:

• to slow down and not accelerate too much

The non applies only to the second action, accelerare.

Here troppo means too much, too fast, or excessively, depending on context.

So:

• accelerare troppo = to accelerate too much / to speed up too much

In Italian, adverbs like troppo often come after the verb, especially in simple expressions like this.

Compare:

• mangiare troppo = to eat too much
• parlare troppo = to talk too much
• correre troppo = to run too much / too fast

So the word order is normal.

They are opposites:

• rallentare = to slow down
• accelerare = to accelerate / speed up

In a driving context, rallentare is very common when talking about reducing speed for safety.

So the sentence gives a clear contrast:

• when it rains, you should slow down
• and not speed up too much

The present tense is used because the sentence expresses a general truth or habitual situation.

• Quando piove, bisogna rallentare. = When it rains, you need to slow down.

This is not describing just one specific moment. It is stating a rule that applies whenever that situation happens.

Italian often uses the present tense this way, just like English does in sentences such as When it rains, the roads get slippery.

Because Quando piove is an introductory subordinate clause, and in Italian it is very common to separate it from the main clause with a comma.

So the structure is:

• Quando piove, = introductory clause
• bisogna rallentare... = main clause

This is similar to English punctuation in a sentence like:

• When it rains, you need to slow down.

The comma helps make the sentence easier to read.

Yes, depending on context, Quando piove can be understood as either:

• When it rains
• When it’s raining

In this sentence, the idea is general safety advice, so When it rains or Whenever it’s raining both work well.

Italian piove does not force exactly the same distinction that English sometimes makes between it rains and it’s raining. Context decides the most natural translation.

Yes. Bisogna usually sounds stronger than a simple suggestion. It expresses necessity, good practice, or a rule.

So this is closer to:

• You have to slow down
• One must slow down

rather than:

• It would be better to slow down
• You should maybe slow down

That makes sense here, because the sentence is giving safety advice.