Polisi mengawasi jalan.

Indonesian normally does not use articles the way English does. So polisi can mean the police, a police officer, or police officers, depending on context. Likewise, jalan can mean the road, a road, or the street.

So Polisi mengawasi jalan could be understood in English as:

• The police are monitoring the road
• A police officer is watching the street
• Police are watching the road

Context tells you which one is most natural.

It can mean either. Indonesian nouns usually do not change form for singular vs. plural.

So polisi may refer to:

• a police officer
• the police
• police officers

If the speaker wants to make plurality very clear, they might use context, a number, or sometimes reduplication in some cases. But in a sentence like this, polisi is naturally ambiguous.

Because awas by itself is not the normal finite verb meaning to monitor/watch over something in this sentence.

The form mengawasi is built from:

• meng- = an active verb prefix
• awas = a base related to being alert/watchful
• -i = a suffix often used when the action is directed toward an object or location

So mengawasi means to watch over, to supervise, or to monitor something.

In this sentence, jalan is the thing being watched, so mengawasi is the correct verb form.

The suffix -i often gives a verb the sense of acting on, toward, or over an object, sometimes especially a place, target, or repeated focus.

With mengawasi, it helps form the meaning to keep watch over or to monitor something.

So:

• mengawasi jalan = to monitor/watch the road

You do not need to translate -i as a separate English word every time, but it is part of what makes the verb mean what it does.

Yes. This sentence follows the common Indonesian pattern:

Subject + Verb + Object

So:

• Polisi = subject
• mengawasi = verb
• jalan = object

That makes it very similar to English word order:

• Police watch the road

Not by itself. Indonesian verbs do not change form for tense the way English verbs do.

So mengawasi could mean:

• watch
• is watching
• are watching
• was watching
• will watch

The time is usually understood from context or from time words such as:

• sekarang = now
• kemarin = yesterday
• besok = tomorrow

Without extra context, English often translates this kind of sentence in the present: The police are monitoring the road or Police monitor the road.

Because jalan is the direct object of the verb mengawasi. In Indonesian, transitive verbs usually take their object directly, without a preposition.

So:

• Polisi mengawasi jalan = The police monitor the road

You do not need something like to or at here.

It can mean different things depending on how it is used.

As a noun, jalan often means:

• road
• street
• way

As a verb, jalan can also mean:

• to walk
• to run/function/go, depending on context

In Polisi mengawasi jalan, it is clearly a noun, because it comes after the transitive verb mengawasi as the object. So here it means the road/street.

A simple pronunciation guide is:

mengawasi ≈ muh-ngah-WAH-see

A few helpful notes:

• ng is like the sound in English sing
• a is usually like a in father
• the final i sounds like ee

So try something close to: muh-ngah-WAH-see

Yes, depending on context, that can be a natural translation. But mengawasi is usually closer to:

• monitor
• watch
• keep an eye on
• supervise

If you specifically want guard in the sense of protecting, Indonesian might also use other verbs depending on context, such as menjaga.

So:

• mengawasi jalan = watching/monitoring the road
• menjaga jalan = guarding the road

They are related, but not exactly the same.

Yes. Adding sedang makes the ongoing aspect clearer, similar to English is/are ...-ing.

So:

• Polisi mengawasi jalan = Police monitor the road / are monitoring the road
• Polisi sedang mengawasi jalan = The police are currently monitoring the road

The version without sedang is still perfectly normal, especially when context already makes the time clear.