Begitu jalanan licin, dia langsung mengurangi kecepatan dan menekan rem lebih hati-hati.

In this sentence, begitu means as soon as, when, or once.

So Begitu jalanan licin means something like:

• As soon as the road became slippery
• When the road was slippery
• Once the road got slippery

This is different from other uses of begitu, which can also mean like that or that way in other contexts.

Indonesian often leaves out the verb to be.

So:

• jalanan licin = the road is slippery
• literally: road slippery

You do not need adalah here. In fact, adalah would sound unnatural in this kind of everyday descriptive sentence.

Both relate to road/street, but jalanan often feels more like the roadway / the streets / the road surface, and it can sound a bit more colloquial or concrete than plain jalan.

In this sentence, jalanan licin sounds very natural for the road is slippery.

Very roughly:

• jalan = road, street, way
• jalanan = roadway / street area / roads, often in a more everyday tone

Langsung means immediately, right away, or straightaway.

So dia langsung mengurangi kecepatan means:

• he/she immediately reduced speed
• he/she slowed down right away

It shows a quick reaction to the slippery road.

Mengurangi kecepatan literally means to reduce speed.

It is a very natural way to say slow down, especially when talking about driving.

Compare:

• mengurangi kecepatan = reduce speed
• melambat = slow down, become slower
• memperlambat = slow something down

So this sentence focuses on the driver's action of lowering speed.

Yes, both are possible.

• menekan rem = press the brake
• mengerem = brake

In this sentence, menekan rem is very literal and clear: the person physically presses the brake.

So:

• dia menekan rem = he/she pressed the brake
• dia mengerem = he/she braked

Both are natural, but menekan rem highlights the actual action more directly.

Lebih hati-hati means more carefully or more cautiously.

The comparison does not always need to be stated explicitly in Indonesian. It often means:

• more carefully than before
• more carefully than usual
• more carefully because of the situation

So here it suggests that, because the road was slippery, the person pressed the brake with extra caution.

It can be dengan lebih hati-hati, and that would also be correct.

Indonesian often omits dengan when using expressions like this adverbially.

So both are possible:

• menekan rem lebih hati-hati
• menekan rem dengan lebih hati-hati

The version without dengan is very common and natural.

Grammatically, it most directly modifies the nearest verb phrase, which is menekan rem.

So the most direct reading is:

• he/she immediately reduced speed
• and pressed the brake more carefully

However, in real context, listeners may understand the whole reaction as cautious. If you wanted to make it clearly apply to both actions, you could restructure the sentence.

Both dia and ia can mean he or she.

The difference is mainly style and grammar:

• dia is very common in everyday Indonesian
• ia is a bit more formal or literary

Also, ia is mainly used as a subject, while dia is more flexible.

So dia is the most natural choice in a sentence like this.

Indonesian usually does not mark tense the way English does.

This sentence could mean different things depending on context:

• past: when the road got slippery, he immediately slowed down...
• present/general: whenever the road is slippery, he immediately slows down...
• narrative: as soon as the road was slippery, he...

So the time reference comes from the wider context, not from the verb forms themselves.

Yes, the comma is helpful because Begitu jalanan licin is an introductory clause.

It separates:

• the trigger/situation: Begitu jalanan licin
• the main action: dia langsung mengurangi kecepatan dan menekan rem lebih hati-hati

Without the comma, the sentence may still be understandable, but the punctuation with the comma is clearer and more natural in writing.