Na drugim rondzie nie widziałam znaku i pojechałam nie tam, gdzie trzeba.

Because na drugim rondzie describes the location/situation where something happened: at the second roundabout.

In Polish, na can take different cases depending on the meaning:

• na + accusative = motion toward a place
  
  • wjechałam na rondo = I drove onto the roundabout
• na + locative = being at/in that place
  
  • na rondzie = on/at the roundabout

So in this sentence, the speaker is saying where the problem happened, not emphasizing movement onto the roundabout.

Also:

• drugim is the locative singular form of drugi (second)
• rondzie is the locative singular of rondo

So:

• na drugim rondzie = at the second roundabout

Because after na in this meaning, Polish uses the locative case, and rondo changes form in the locative:

• nominative: rondo
• locative: rondzie

This kind of change is normal. Many neuter nouns ending in -o change to -e or -ie in certain cases.

So:

• to jest rondo = this is a roundabout
• na rondzie = at/on the roundabout

The ending -am shows that the speaker is female and is talking about the past.

In Polish past tense, verbs agree with the gender of the speaker:

For a woman:

• widziałam = I saw / I was seeing
• pojechałam = I went / drove

For a man:

• widziałem
• pojechałem

So this sentence was said by a woman.

Because after negation, Polish often uses the genitive instead of the accusative for the direct object.

Here:

• positive: widziałam znak = I saw the sign / a sign
• negative: nie widziałam znaku = I didn’t see the sign / a sign

So znaku is the genitive singular of znak.

This is a very important pattern in Polish:

• mam czas = I have time
• nie mam czasu = I don’t have time

With widzieć, the genitive after negation is very common and standard.

Here znak most naturally means a road sign or traffic sign.

In general, znak can mean:

• sign
• symbol
• mark
• signal

But in the context of driving and a roundabout, nie widziałam znaku is best understood as I didn’t see the sign.

Because pojechałam is perfective, and it presents the action as a completed event: the speaker ended up going in the wrong direction.

Compare:

• jechałam = I was driving / I drove (focus on the process)
• pojechałam = I went / drove off (focus on the completed action or result)

In this sentence, the important idea is not just that she was driving, but that she took the wrong way. So pojechałam fits well.

Because the sentence describes two different kinds of actions:

1. nie widziałam znaku
   This is about perception — the speaker failed to see something. Polish often uses the imperfective here: widzieć.

2. pojechałam nie tam
   This is a completed event with a clear result: she ended up going the wrong way. That is why pojechałam (perfective) works well.

So the aspect choice reflects the meaning:

• widzieć = ongoing/general perception
• pojechać = one completed movement/action

Literally, it means:

• nie tam = not there
• gdzie = where
• trzeba = it is necessary / one must

So literally: not there, where it is necessary

But in natural English, it means:

• not where I should have gone
• not where I was supposed to go
• the wrong way

It is a very natural Polish way to express the idea of doing something incorrectly or going to the wrong place.

Trzeba is an impersonal word in Polish. It means:

• it is necessary
• one must
• you have to (in a general sense)

It does not have a normal personal subject like I, you, or he.

Examples:

• Trzeba iść. = One has to go. / It’s necessary to go.
• Trzeba uważać. = You have to be careful.

So gdzie trzeba literally means where it is necessary, but idiomatically it means where one should or where you’re supposed to.

Because gdzie trzeba is a very natural, idiomatic, and slightly more general expression.

Compare:

• pojechałam nie tam, gdzie trzeba
  = I went not where I should have / I went the wrong way
• pojechałam nie tam, gdzie powinnam była
  = I went not where I should have gone

The version with powinnam była is more explicit and more personal, but also heavier.
The version with trzeba sounds smoother and more idiomatic in everyday speech.

Because the speaker is negating the destination/location:

• tam = there
• nie tam = not there

So the idea is: I went not there where I should have
= I went somewhere else, not the correct place/direction

This is the natural way to say it in Polish.

I simply means and. It joins the two parts of the sentence:

• nie widziałam znaku = I didn’t see the sign
• pojechałam nie tam, gdzie trzeba = and I went the wrong way

So the whole sentence is a sequence of cause and result:

• I didn’t see the sign,
• and then I went the wrong way.

In English, the most natural translation is usually at the second roundabout.

Polish na rondzie literally uses na, which often corresponds to on, but with roundabouts English normally says at.

So:

• na drugim rondzie = at the second roundabout

Sometimes in context it may feel close, but literally it means I didn’t see the sign.

If you specifically wanted to say I couldn’t see the sign, Polish might use something like:

• nie mogłam zobaczyć znaku
• nie było widać znaku (depending on context)

In your sentence, nie widziałam znaku most directly means that the speaker simply failed to notice or see it.

Because gdzie trzeba introduces a subordinate clause.

The structure is:

• nie tam = main part
• gdzie trzeba = dependent clause explaining where

Polish normally uses commas before clauses introduced by words like:

• gdzie = where
• który = which/who
• że = that
• bo = because

So the comma here is standard and necessary.

Yes, but the verb forms would change:

• Na drugim rondzie nie widziałem znaku i pojechałem nie tam, gdzie trzeba.

The only difference is the masculine past tense endings:

• widziałem instead of widziałam
• pojechałem instead of pojechałam

Yes, very common.

You can use this pattern in many situations, not only for driving:

• Usiadłem nie tam, gdzie trzeba.
  = I sat in the wrong place.
• Wpisała adres nie tam, gdzie trzeba.
  = She entered the address in the wrong place.
• Kliknąłem nie tam, gdzie trzeba.
  = I clicked in the wrong place.

It is a useful idiomatic expression meaning not where one should / in the wrong place / the wrong way.