Il traffico è bloccato dalla pioggia.

Because traffico is a masculine singular noun that begins with tr-, and that takes the regular masculine singular article il.

Use:

• il before most masculine singular nouns: il libro, il tavolo, il traffico
• lo before masculine singular nouns beginning with s + consonant, z, ps, gn, x, and a few others: lo studente, lo zaino
• l' before masculine singular nouns beginning with a vowel: l'amico

So il traffico is the correct form.

Traffico is masculine singular.

A useful clue is the ending -o, which often signals a masculine singular noun in Italian:

• il traffico
• il treno
• il problema is an exception, so endings are only a clue, not a guarantee.

You can also see the gender from the words agreeing with it:

• il = masculine singular article
• bloccato = masculine singular past participle/adjective form

È bloccato is a passive structure, meaning is blocked.

Breakdown:

• è = is
• bloccato = blocked

So the sentence literally works like:

• The traffic is blocked by the rain.

Compare:

• blocca = blocks → active, as in La pioggia blocca il traffico
• ha bloccato = has blocked → active past, as in La pioggia ha bloccato il traffico

The sentence you have uses the passive because the focus is on the traffic, not on the rain.

Because it agrees with traffico, which is masculine singular.

In Italian, the past participle in a passive construction behaves like an adjective and agrees with the subject:

• masculine singular: bloccato
• feminine singular: bloccata
• masculine plural: bloccati
• feminine plural: bloccate

Examples:

• Il traffico è bloccato
• La strada è bloccata
• I treni sono bloccati
• Le auto sono bloccate

Dalla means by the here.

It is a contraction of:

• da + la = dalla

In a passive sentence, da introduces the agent or cause:

• Il traffico è bloccato dalla pioggia = The traffic is blocked by the rain

Other common contractions with da:

• dal = da + il
• dallo = da + lo
• dai = da + i
• dagli = da + gli
• dalle = da + le

Because pioggia is a specific noun here and normally takes an article in Italian.

So:

• la pioggia = the rain
• da + la pioggia = dalla pioggia

Italian often uses articles where English does not. English may say by rain only in very special contexts, but Italian naturally says dalla pioggia.

It can feel like both, and that is very common in Italian.

Il traffico è bloccato dalla pioggia can be understood as:

• a passive: the traffic is blocked by the rain
• a resulting state: the traffic is in a blocked condition because of the rain

In everyday usage, Italians often use essere + past participle this way without sharply separating the two ideas.

Yes. That is the active version.

Compare:

• Il traffico è bloccato dalla pioggia = passive
• La pioggia blocca il traffico = active

Both are correct, but they focus on different things:

• passive focuses on the traffic
• active focuses on the rain

Yes, and it is very natural.

There is a small nuance:

• dalla pioggia presents the rain more directly as the thing causing the blockage
• per la pioggia means because of the rain

So both work, but:

• bloccato dalla pioggia sounds more like a passive cause
• bloccato per la pioggia sounds more like a reason or circumstance

In everyday speech, per la pioggia is often very common.

Italian passives are commonly formed with essere:

• Il traffico è bloccato dalla pioggia

You can sometimes also find venire in passive sentences, especially to emphasize the action more than the state:

• Il traffico viene bloccato dalla pioggia

But in this sentence, è bloccato is the most natural and common choice.

Both the verb and bloccato would change to agree with the new subject.

Examples:

• Le strade sono bloccate dalla pioggia = The roads are blocked by the rain
• I treni sono bloccati dalla pioggia = The trains are blocked by the rain

So agreement changes like this:

• è → sono
• bloccato → bloccati / bloccate, depending on gender

No. Like English traffic, Italian traffico is normally an uncountable noun in this meaning.

You say:

• C'è traffico = There is traffic
• Il traffico è bloccato = The traffic is blocked

You would not normally use it like a regular count noun meaning one traffic.

Pioggia is pronounced approximately PYO-jja.

A few pronunciation notes:

• pio- sounds roughly like pyo
• gg before i gives a sound like the j in jam, but stronger/longer
• -ia at the end is part of the final syllable pattern

The double consonant matters in Italian because consonant length can affect pronunciation and rhythm. Even if learners do not fully master consonant length at first, it is good to notice that gg is not accidental.

Yes, but that means something slightly different.

• Il traffico è bloccato dalla pioggia = the traffic is blocked by the rain
• Il traffico si è bloccato = the traffic got blocked / came to a standstill

The si version is not the same passive structure. It suggests that the traffic ended up blocked, often without naming an outside agent. If you want to clearly mention the rain as the cause, the original sentence is better.

Yes. The basic order is:

subject + essere + past participle + da-phrase

So:

• Il traffico è bloccato dalla pioggia

You can move parts around for emphasis, but the basic version is the most neutral and natural.

For example:

• Dalla pioggia, il traffico è bloccato is possible, but much less neutral and more stylistically marked.

For learners, the standard order is the best one to use.