Saat hujan deras, sopir angkot mengurangi kecepatan di jalanan licin.

Saat introduces a time expression, so here it means when or during.

In many contexts, saat and ketika are very similar and both can mean when. In this sentence, either would work:

• Saat hujan deras...
• Ketika hujan deras...

A small nuance:

• saat often feels a bit shorter and slightly more neutral/formal
• ketika can feel a bit more narrative or literary in some contexts

For everyday understanding, you can treat them as near-equivalents here.

Hujan deras is a very common Indonesian combination meaning heavy rain.

• hujan = rain
• deras = heavy, strong-flowing, intense

Indonesian often forms phrases simply by putting a noun and an adjective together:

• hujan deras = heavy rain
• air dingin = cold water
• jalan licin = slippery road

A useful note: deras is especially common with things like rain, water flow, or wind-like force. So it is a very natural word choice here.

Angkot is short for angkutan kota, a type of shared public minibus/van used for local transportation in Indonesia.

So sopir angkot means an angkot driver or a public minibus driver.

This is also a cultural vocabulary item: it refers to a very specific Indonesian kind of transportation, not just any bus.

Yes, sopir is the standard Indonesian spelling.

You may also see supir in informal writing, signs, chats, or older usage, because it is very common in real life. But if you are learning standard Indonesian, use sopir.

So in formal writing:

• sopir = preferred standard form

Mengurangi comes from the base kurang, which relates to being less or lacking.

The verb is formed with:

• meN-
  • kurang
    • -i → mengurangi

This gives an active transitive verb meaning to reduce something.

A very useful contrast:

• berkurang = to decrease, to become less
• mengurangi = to reduce something

So:

• Kecepatan berkurang = The speed decreases
• Sopir mengurangi kecepatan = The driver reduces the speed

Also notice the spelling change: when meN- is added to a root beginning with k, the k usually disappears:

• kurang → mengurangi

Because kecepatan is a noun, while cepat is usually an adjective.

• cepat = fast
• kecepatan = speed

The verb mengurangi normally takes a thing as its object, and here that thing is speed:

• mengurangi kecepatan = reduce speed

This is a very common pattern in Indonesian:

• cepat → kecepatan = fast → speed
• tinggi → ketinggian = high → height/altitude
• dalam → kedalaman = deep → depth

Here di is a preposition, meaning in, on, or at.

So:

• di jalanan licin = on the slippery road / on slippery streets

This is not the passive prefix di-.

A very important spelling rule in Indonesian:

• di as a preposition is written separately
• di- as a passive verb prefix is written attached

Compare:

• di jalan = on the road
• dikurangi = reduced

So in your sentence, di jalanan licin is a location phrase.

Jalan means road, street, or way.

Jalanan often refers more to the road/street area in a broader or more physical sense, and can sound a bit like the roadway, the streets, or the road surface/road area, depending on context.

So:

• di jalan licin = on a slippery road
• di jalanan licin = on slippery roads / on the slippery roadway / in slippery street conditions

In this sentence, jalanan helps give a natural sense of real road conditions, not just an abstract road.

Because Indonesian commonly puts a noun directly before an adjective:

• jalanan licin = slippery road(s)
• mobil baru = new car
• rumah besar = big house

You do not need yang here.

Using yang is possible in some contexts, but it usually makes the phrase more explicit or descriptive:

• jalanan yang licin

That is grammatical, but in this sentence it is more natural and efficient to say simply jalanan licin.

Because Indonesian usually does not mark articles the way English does.

There is no direct equivalent that must always be used for:

• a
• an
• the

And nouns often do not have to show plural unless the speaker wants to emphasize it.

So:

• sopir angkot can mean an angkot driver, the angkot driver, or just angkot drivers in another context, depending on context
• jalanan licin can mean a slippery road, the slippery road, or slippery roads/streets, depending on context

English requires those choices more explicitly; Indonesian often leaves them to context.

Yes, the word order is flexible.

The sentence starts with the time phrase:

• Saat hujan deras, ...

This is very natural because it sets the scene first.

You could also say:

• Sopir angkot mengurangi kecepatan di jalanan licin saat hujan deras.

That is also understandable and grammatical.

The main difference is emphasis:

• Saat hujan deras, ... emphasizes the situation first
• putting saat hujan deras later gives the main action first

When the time phrase comes first, a comma is commonly used in writing.

Yes, this is an active sentence.

The subject is the doer of the action:

• sopir angkot = the driver
• mengurangi = reduces

Indonesian does allow passive sentences, but the active form is the most natural here because the driver is the clear actor.

A passive version is possible, such as:

• Saat hujan deras, kecepatan dikurangi oleh sopir angkot di jalanan licin.

That is grammatical, but it sounds less natural in ordinary conversation because it focuses on the speed rather than the driver.

So for everyday usage, the active sentence is the better model.

Yes, it could.

• mengurangi kecepatan = reduce speed
• memperlambat = slow down something / make something slower

So you could say:

• Saat hujan deras, sopir angkot memperlambat kendaraan di jalanan licin.

But in your original sentence, mengurangi kecepatan is very straightforward and natural, especially because the object is explicitly speed.

So both are fine, but they are structured slightly differently:

• mengurangi kecepatan focuses on speed
• memperlambat kendaraan focuses on the vehicle becoming slower