Jeg bliver sur, hvis trafikken er tæt, og bussen er forsinket igen.

Bliver sur means becomes angry / gets annoyed, so it focuses on a change of state.

• Jeg er sur = I am angry
• Jeg bliver sur = I get angry / I become angry

In this sentence, Danish is saying that this situation causes the speaker to get annoyed.

Sur usually means angry, annoyed, or cross.

In everyday speech, it often sounds a bit less dramatic than rasende (furious). In this sentence, Jeg bliver sur is very natural for I get annoyed / I get angry.

Literally, it means the traffic is dense.

In more natural English, that would usually be:

• the traffic is heavy
• there is a lot of traffic

So tæt means close, dense, or packed tightly together, and with traffic it gives the idea of congestion.

In Danish, the definite article is usually added to the end of the noun.

So:

• en trafik is not normally used this way, but trafikken = the traffic
• en bus = a bus
• bussen = the bus

This is one of the big differences from English. Instead of putting the before the noun, Danish often adds -en, -et, or another definite ending to the noun itself.

This is mainly a spelling pattern.

The noun is:

• en bus
• definite singular: bussen

Danish often doubles the final consonant in spelling when an ending is added, especially to keep the short vowel sound clear. So you learn it as the standard definite form: bussen.

Here, forsinket works like an adjective and means delayed.

The full part:

• bussen er forsinket = the bus is delayed

It comes from the verb at forsinke (to delay), and forsinket is the past participle form, which is often used adjectivally.

So in this sentence, it describes the state of the bus.

Danish often uses the present tense for general truths, habits, and typical reactions, just like English does.

So:

• Jeg bliver sur, hvis ... = I get angry if ...

This does not have to mean it is happening right now. It can mean:

• whenever this happens
• in that kind of situation
• as a general reaction

Hvis means if.

It introduces a conditional clause:

• hvis trafikken er tæt = if the traffic is heavy
• hvis ... og ... = if ... and ...

In your sentence, hvis covers both conditions:

• if the traffic is heavy
• and the bus is delayed again

So the speaker gets annoyed in that situation.

Because hvis introduces a subordinate clause, and Danish subordinate clauses normally keep the subject before the verb.

So:

• hvis trafikken er tæt = subordinate clause
• subject: trafikken
• verb: er

That is normal Danish subordinate-clause word order.

By contrast, in a main clause Danish often follows verb-second order.

Because the sentence begins with the main clause:

• Jeg bliver sur
• then the hvis clause comes after it

So the main clause keeps its normal order.

If the conditional clause came first, then the main clause would show inversion:

• Hvis trafikken er tæt, og bussen er forsinket igen, bliver jeg sur.

Notice the difference:

• Jeg bliver sur, hvis ...
• Hvis ..., bliver jeg sur.

That second version is very common in Danish.

Yes. Og means and, and here it joins two coordinated clauses:

• trafikken er tæt
• bussen er forsinket igen

Both belong under the condition introduced by hvis.

So the meaning is basically:

• I get annoyed if the traffic is heavy and the bus is delayed again.

Igen means again.

Here it modifies the idea that the bus is delayed one more time:

• bussen er forsinket igen = the bus is delayed again

Putting igen at the end is very natural in Danish. Adverbs often appear later in the clause, especially in simple statements like this one.

Sometimes, but the meaning changes slightly.

• hvis = if
• når = when / whenever

So:

• Jeg bliver sur, hvis trafikken er tæt ... = I get annoyed if the traffic is heavy ...
• Jeg bliver sur, når trafikken er tæt ... = I get annoyed when/whenever the traffic is heavy ...

Hvis sounds more conditional. Når sounds more like something that actually happens repeatedly or is expected to happen.

Yes, absolutely:

• Hvis trafikken er tæt, og bussen er forsinket igen, bliver jeg sur.

That is fully correct and very natural.

The main difference is word order in the second part:

• after a fronted clause, Danish uses inversion
• so bliver jeg sur, not jeg bliver sur

Yes. Danish can express the same idea in different ways.

For example:

• hvis trafikken er tæt = if the traffic is heavy
• hvis der er tæt trafik = if there is heavy traffic

Both are natural, though der er tæt trafik is often especially idiomatic when talking about traffic conditions.

Yes, it is natural and understandable.

A native speaker might also say things like:

• Jeg bliver sur, hvis der er tæt trafik, og bussen er forsinket igen.
• Jeg bliver irriteret, hvis trafikken er tæt, og bussen er forsinket igen.

But your sentence is perfectly normal Danish.