Menurut saya, nekat berkendara saat hujan deras itu tidak bijak.

Menurut saya means in my opinion or according to me.

• menurut = according to
• saya = I / me

So this phrase introduces a personal opinion. It is a very common and natural way to begin a sentence when you want to sound polite or neutral.

A more casual version would be menurutku.

Nekat is a useful word that means something like:

• reckless
• rash
• bold in a dangerous way
• doing something even though you know it is risky

So nekat berkendara is not just driving. It means going ahead and driving anyway, despite the danger.

That is why nekat adds a strong negative sense here.

It is basically an adjective, but in Indonesian adjectives can often appear before a verb and describe the way an action is done.

So nekat berkendara feels like:

• to recklessly drive
• or more literally, to be reckless enough to drive

This is very normal in Indonesian. You do not need a special adverb ending like -ly in English.

Berkendara means to travel by vehicle / to operate a vehicle. It is fairly general.

It can refer to things like:

• driving a car
• riding a motorcycle
• using a vehicle in general

Mengemudi is closer to to drive in the sense of steering or operating a vehicle, especially a car.

So:

• berkendara = more general
• mengemudi = more specifically driving

In this sentence, berkendara works well because it is broad and fairly neutral in style.

Saat means when or during.

Hujan deras means heavy rain.

So saat hujan deras means:

• when it is raining heavily
• during heavy rain

A few close alternatives are:

• ketika hujan deras
• waktu hujan deras

All are understandable, though saat sounds a bit neat and standard.

Deras is a common adjective for something that falls or flows strongly. With hujan, it means heavy or intense rain.

So hujan deras = heavy rain.

Another common phrase is hujan lebat, which also means heavy rain. Both are natural.

This itu points back to the whole action before it and helps make that action the topic or subject of the sentence.

So:

• nekat berkendara saat hujan deras itu
  = that act of recklessly driving in heavy rain

It does not translate neatly word-for-word, but in English it is a bit like saying:

• Doing that is not wise
• That kind of action is not wise

In Indonesian, itu often helps package a whole phrase into something the speaker can comment on.

Yes. You could say:

Menurut saya, nekat berkendara saat hujan deras tidak bijak.

That is still understandable and natural.

Adding itu makes the sentence feel a little more clearly structured, because it marks the earlier phrase as the thing being judged. In many cases, both versions are possible.

Because bijak is an adjective.

In Indonesian:

• tidak negates verbs and adjectives
• bukan usually negates nouns or noun phrases

So:

• tidak bijak = not wise
• bukan bijak would be wrong here

This is a very important Indonesian pattern.

Because Indonesian often does not use a copula like English is/are in simple present statements.

So:

• itu tidak bijak literally looks like that not wise
• but it naturally means that is not wise

This is completely normal Indonesian grammar.

A simple way to break it down is:

• Menurut saya = in my opinion
• nekat berkendara saat hujan deras itu = the act of recklessly driving in heavy rain
• tidak bijak = is not wise

So the sentence structure is basically:

In my opinion + [that action] + is not wise

The subject is not one word; it is the whole action phrase.

They are very close.

• bijak = wise, prudent
• bijaksana = wise, judicious, often a bit more formal or fuller-sounding

In this sentence, tidak bijak sounds very natural.
You could also say tidak bijaksana, and the meaning would stay almost the same.

It sounds neutral to slightly formal, mainly because of words like:

• menurut saya
• berkendara
• bijak

A more casual version might be:

Menurutku, nekat nyetir waktu hujan deras itu nggak bijak.

Differences:

• menurutku = more casual than menurut saya
• nyetir = casual for driving
• nggak = casual for tidak

So the original sentence is perfectly natural, but it sounds more careful and standard than everyday casual speech.