Learn Hardcore Indonesian: Ketika lalu lintas macet, klakson mobil terdengar hampir tanpa berhenti. - When traffic is jammed, car horns are heard almost without stopping.

Literally, lalu ≈ to pass by and lintas ≈ to cross/pass through, but in modern Indonesian they almost always function together as a fixed phrase meaning traffic.
You rarely separate them in this sense; you say lalu lintas macet (the traffic is jammed), lalu lintas ramai (the traffic is busy), aturan lalu lintas (traffic rules), etc.
A more colloquial alternative is jalanan (the streets/roads), but lalu lintas is the standard, neutral term for traffic.

Why is there no word like “is” in lalu lintas macet? Shouldn’t it be “lalu lintas is jammed”?

Indonesian normally does not use a verb like “to be” (is/are) between a noun and an adjective.

Lalu lintas macet literally is: traffic jammed
In English we must say: The traffic is jammed.
In Indonesian, the structure [noun] + [adjective] already means [noun] is [adjective] in most cases.

So:

lalu lintas macet = “the traffic is jammed”
air panas = “the water is hot”
rumah besar = “the house is big”

You only use adalah in specific structures (e.g., between nouns: Ayah saya adalah dokter = My father is a doctor), not here.

Is macet an adjective or a verb? Does it mean “jammed” or “to be jammed”?

In practice, macet behaves like an adjective that can also function a bit like a stative verb (“to be jammed”).

As an adjective:
- lalu lintas macet = “the traffic is jammed”
- jalan macet = “the road is congested”
As a kind of stative verb (very similar meaning):
- Lalu lintas macet lagi. = “The traffic is jammed again.”

Indonesian often does not sharply separate adjectives and “stative verbs” the way English does. Words like macet, panas, dingin can cover both “is jammed / hot / cold” and “jammed / hot / cold” depending on context.

What is the difference between ketika, saat, waktu, and kalau for “when”?

All can relate to time, but they differ in tone and usage:

ketika
- Neutral, a bit formal or written.
- Used for specific points/periods in time.
- Ketika lalu lintas macet, … = When the traffic is jammed, …
saat
- Very common in both spoken and written Indonesian.
- Similar to “at the time (when)” or “while”.
- Saat lalu lintas macet, … is a very natural alternative.
waktu
- Literally “time”, but also used as “when” in spoken language.
- Waktu lalu lintas macet, … sounds more conversational/colloquial.
kalau
- Primary meaning: if.
- In everyday speech it can also mean when/whenever, especially for repeated situations.
- Kalau lalu lintas macet, klakson mobil terdengar… ≈ “When(ever) the traffic is jammed, car horns can be heard …”
- It sounds more informal and more like a general condition.

In your sentence, ketika feels slightly more neutral/formal and descriptive; kalau would sound more like talking about a typical repeated situation in everyday speech.

How should I understand klakson mobil? Why is it “car horn” and not “horn car”?

Indonesian noun phrases usually follow the pattern [main noun] + [modifier].

klakson mobil
- klakson = horn
- mobil = car
- So literally: horn (of the) car → “car horn(s)”.

The first noun (klakson) is the main thing; the second noun (mobil) tells you whose/what kind of horn it is.

Other examples:

rumah guru = the teacher’s house
roda mobil = car wheel(s)
pintu rumah = the door of the house / house door

How is plural expressed in klakson mobil? How do we know it’s “car horns” and not just “car horn”?

Indonesian usually does not mark plural on the noun if it’s clear from context.

klakson mobil could mean:
- “a car horn”
- “car horns”
- “the car horn(s)”

In your sentence, because we’re talking about traffic and a general situation, it’s naturally understood as many car horns.

If you really want to emphasize plurality, you can repeat the noun or add a word like banyak (many):

klakson-klakson mobil = horns of the cars (sounds a bit heavy and rarely needed here)
banyak klakson mobil = many car horns

But usually klakson mobil alone is enough; context does the work.

What does terdengar mean, and how is it different from mendengar or kedengaran?

terdengar = can be heard / is heard / audible
- Focuses on the sound existing / being heard, not on the person who hears.
- In your sentence:
  - klakson mobil terdengar ≈ “car horns can be heard / are audible”.
mendengar = to hear (active verb; someone does the hearing)
- Saya mendengar klakson. = I hear a horn.
kedengaran
- More colloquial.
- Can mean to be heard / sound like.
- Klakson mobil kedengaran terus. = The car horns keep being heard (informal).

terdengar is slightly more neutral/formal and impersonal. It suits written or descriptive language well, like in your sentence.

How does hampir tanpa berhenti work grammatically? Why not just hampir tidak berhenti?

Breakdown:

hampir = almost
tanpa = without
berhenti = to stop

So hampir tanpa berhenti = almost without stopping.

You could also say hampir tidak berhenti (“almost do not stop”), which is understandable, but:

tanpa
- verb = “without [doing] …”
  - tanpa berhenti = without stopping
  - Adding hampir sounds a bit more fluent/natural here: “almost without stopping”.

Hampir tanpa berhenti emphasizes the continuous, uninterrupted nature of the sound: the car horns are heard almost continuously, with hardly any pause.

What is the word‑for‑word (literal) breakdown of the sentence?

Ketika = when
lalu lintas = traffic
macet = jammed / congested
, = (comma separating the time clause and the main clause)
klakson mobil = car horn(s)
terdengar = are heard / can be heard / are audible
hampir = almost
tanpa = without
berhenti = stopping

Literal ordering:
When traffic jammed, car horns heard almost without stopping.

Natural English:
When the traffic is jammed, car horns can be heard almost without stopping.

Does this sentence refer to past, present, or future? How is tense understood in Indonesian here?

Indonesian verbs usually do not change form for tense. The same sentence can describe:

A general truth / habitual situation:
- “Whenever the traffic is jammed, car horns can be heard almost non‑stop.”
A specific past event (with context):
- “Yesterday, when the traffic was jammed, car horns were heard almost non‑stop.”
A possible future situation (with context):
- “Later, when the traffic is jammed, car horns will be heard almost non‑stop.”

Tense is inferred from context or from time expressions (like kemarin = yesterday, nanti = later). The sentence itself is tenseless; English translators choose the most suitable tense based on context.