Я тебя предупреждал, что на этой дороге легко проехать нужный поворот.

Both are possible, but they feel a little different.

Предупреждал is the imperfective past. Here it often means something like:

• I had warned you
• I did warn you
• I told you before

It can sound like the speaker is reminding the other person of an earlier warning, sometimes with a slight I told you so tone.

Предупредил is perfective and would focus more on one completed act of warning: I warned you once, and that warning was delivered.

So Я тебя предупреждал... is very natural if the speaker is referring back to a previous warning.

Because предупреждать takes a direct object: you warn someone.

• ты = you as the subject
• тебя = you as the object

So:

• Я предупреждал тебя = I warned you

This is just the normal accusative form of the pronoun.

Russian commonly uses this pattern:

предупреждать / предупредить кого-то, что...

So the structure is:

• Я тебя предупреждал = I warned you
• что... = that...

Together:

Я тебя предупреждал, что... = I warned you that...

You can also sometimes hear a slightly fuller version like предупреждать о том, что..., but in everyday Russian, что by itself is very common.

Because что introduces a subordinate clause.

Russian punctuation requires a comma before a subordinate clause introduced by words like:

• что = that
• когда = when
• если = if
• потому что = because

So:

Я тебя предупреждал, что...

is punctuated the normal Russian way.

На этой дороге means on this road in the sense of on this stretch of road / on this road as a location or setting.

That works well here because the sentence is describing a general characteristic of the road:

• На этой дороге легко... = On this road, it’s easy to...

По этой дороге would emphasize movement along the road:

• По этой дороге легко проехать нужный поворот is also understandable and possible.

The difference is subtle:

• на этой дороге = on this road, in this place/situation
• по этой дороге = while going along this road

In this sentence, на этой дороге sounds very natural.

Because Russian often uses impersonal constructions without a dummy subject like English it.

So English says:

• It is easy to miss the turn

Russian simply says:

• Легко проехать нужный поворот

Literally, that is more like:

• Easy to drive past the needed turn

This is completely normal in Russian. Words like легко, трудно, можно, нельзя often work this way.

Because the sentence is talking about a single result: ending up past the turn.

Проехать is perfective, so it fits the idea of:

• to drive past it
• to miss it in one instance

The focus is on the completed outcome: you were supposed to turn, but now you have already gone past it.

If you used проезжать, that would sound more like a repeated or habitual action, or it would shift the nuance away from one completed miss.

So:

• легко проехать нужный поворот = easy to drive past / miss the turn
• легко проезжать... would not fit as naturally here

Literally, it means to drive past the turn you need.

In more natural English, that is:

• to miss the right turn
• to drive past your turn

This use of проехать is very common with places or points on a route:

• проехать остановку = go past the bus stop
• проехать дом = go past the house
• проехать поворот = go past the turn

So the idea is not just drive through a turn, but fail to take it and continue past it.

Very often, yes.

Many learners first meet:

• пропустить поворот = to miss the turn

That is extremely common and very natural.

Проехать поворот is also natural, but it is a bit more literal from the driving perspective: to drive past the turn.

So the two are close:

• пропустить нужный поворот = miss the turn
• проехать нужный поворот = drive past the turn

In this sentence, проехать emphasizes the physical idea of continuing along the road and passing the turn without taking it.

Yes, literally нужный means needed, but in context it often means:

• the one you need
• the correct one
• the right one

So нужный поворот means:

• the turn you need to take
• the right turn

This is very natural Russian. English often says right turn in this kind of situation, but Russian can use нужный to mean the one required for your route.

Yes. It is the direct object of проехать.

The verb here works like:

• проехать что? = drive past what?

Answer:

• нужный поворот

So it is accusative.

However, поворот is a masculine inanimate noun, and in the singular its accusative looks the same as the nominative:

• nominative: поворот
• accusative: поворот

The adjective matches it:

• нужный поворот

That form also looks the same in nominative and accusative because the noun is masculine inanimate.

Yes. Russian word order is flexible.

The given sentence:

Я тебя предупреждал, что на этой дороге легко проехать нужный поворот.

is natural and neutral.

This order gives a smooth flow:

1. the warning
2. the setting — на этой дороге
3. the evaluation — легко
4. the key result at the end — нужный поворот

Putting нужный поворот at the end makes that final idea stand out a bit.

Other orders are possible, for example:

• Я тебя предупреждал, что нужный поворот на этой дороге легко проехать.

That is grammatical, but it sounds a bit less natural in everyday speech.

So the original word order is a good, idiomatic choice.