Det tager længere end et kvarter at komme hjem, hvis trafikken står stille.

In Danish, det tager ... is a very common way to say it takes ... for time.

So:

• Det tager fem minutter = It takes five minutes
• Det tager lang tid = It takes a long time
• Det tager længere end et kvarter = It takes longer than a quarter of an hour

The det here is a dummy subject, just like English it in it takes 10 minutes. It does not refer to a specific thing.

Yes. Længere is the comparative form of lang:

• lang = long
• længere = longer
• længst = longest

Danish often uses long/longer for duration, just like English can:

• Det tager lang tid = It takes a long time
• Det tager længere tid = It takes longer

In this sentence, længere end et kvarter means longer than a quarter of an hour.

A learner might also expect mere end et kvarter. That is also possible in many contexts, but længere feels very natural when talking about duration.

End means than after a comparative.

So:

• længere end = longer than
• større end = bigger than
• mindre end = smaller than

In this sentence:

• længere end et kvarter = longer than a quarter of an hour

This is directly parallel to English.

Because kvarter is a neuter noun in Danish, so it takes et.

• et kvarter = a quarter of an hour / fifteen minutes

Danish nouns are common gender or neuter gender, and the indefinite article must match:

• en bil
• en dag
• et hus
• et kvarter

This is something you simply have to learn with each noun.

In everyday Danish, et kvarter normally means a quarter of an hour, so 15 minutes.

Examples:

• Jeg kommer om et kvarter = I’ll come in 15 minutes
• Det tager et kvarter = It takes 15 minutes

You can also say 15 minutter, which is completely normal. Et kvarter is just a very common and natural time expression.

At komme hjem is the infinitive phrase, meaning to get home or to come home.

• komme = come / get
• at komme = to come / to get
• hjem = home

After det tager ..., Danish commonly uses an infinitive phrase to say what takes time:

• Det tager fem minutter at lave kaffe = It takes five minutes to make coffee
• Det tager lang tid at lære dansk = It takes a long time to learn Danish
• Det tager længere end et kvarter at komme hjem = It takes longer than a quarter of an hour to get home

So the at is there for the same reason English uses to.

This is a very common question.

• hjem usually expresses movement toward home
• hjemme usually expresses location at home

So:

• Jeg går hjem = I’m going home
• Jeg er hjemme = I’m at home

In your sentence, there is movement: at komme hjem = to get home / to come home, so hjem is correct.

You would not say at komme hjemme here.

Hvis means if.

So:

• hvis trafikken står stille = if the traffic is at a standstill

This gives a condition: under that condition, getting home takes longer.

Could you use når? Usually no, not if you mean a condition like English if.

• hvis = if
• når = when

So:

• Hvis trafikken står stille, tager det længere tid = If traffic is at a standstill, it takes longer
• Når trafikken står stille, tager det længere tid = When traffic is at a standstill, it takes longer

The second version sounds more like something that happens whenever that situation occurs, almost as a general repeated fact. Hvis is the normal choice for if.

Literally, står stille means stands still.

So:

• trafikken = the traffic
• står stille = is standing still / is not moving

This is a normal Danish expression for traffic that is not moving because of congestion, a jam, or a complete standstill.

It is very similar to English expressions like:

• traffic is at a standstill
• traffic isn’t moving

So although it may sound slightly odd if translated word for word, it is completely natural Danish.

Because trafikken is the definite form: the traffic.

• trafik = traffic
• trafikken = the traffic

Danish often puts the definite article at the end of the noun instead of using a separate word like English the.

Compare:

• en bil = a car
• bilen = the car
• en vej = a road
• vejen = the road
• trafikken = the traffic

Here it is talking about traffic in general in the situation described, so trafikken is natural.

Danish often uses the present tense for general truths, habits, and also for future meaning when the context is clear.

So:

• Det tager længere end et kvarter ... can mean it takes longer than 15 minutes
• It can also naturally be understood as it will take longer than 15 minutes

Likewise:

• hvis trafikken står stille = if the traffic is at a standstill

This is very similar to English, which also often uses the present in if-clauses:

• If traffic is bad, it takes longer
• not usually If traffic will be bad...

So the present tense here is completely normal.

In the clause hvis trafikken står stille, the word order is normal for a subordinate clause:

• hvis
  • subject + verb + other elements

Here there is no extra adverb causing anything noticeable, so it looks quite similar to English.

A useful thing to know is that Danish subordinate clauses do differ from main clauses when sentence adverbs are present. For example:

• Han kommer ikke = He is not coming
• ... hvis han ikke kommer = ... if he is not coming

In subordinate clauses, adverbs like ikke usually come before the finite verb.

But in your sentence there is no such adverb, so the clause simply appears as:

• hvis trafikken står stille

Yes, many Danes would understand it, and mere end et kvarter is also natural in many situations.

But there is a slight difference in feel:

• mere end et kvarter = more than a quarter of an hour
• længere end et kvarter = longer than a quarter of an hour

When talking specifically about duration, længere often sounds especially natural because it focuses on time being longer. Mere end is more general and often focuses on quantity.

So both are possible, but længere is a very good choice here.

In many contexts, komme hjem corresponds more naturally to English get home, especially after det tager:

• Det tager 20 minutter at komme hjem = It takes 20 minutes to get home

A very literal translation would be to come home, and that is not wrong, but in English get home often sounds more idiomatic in time expressions.

So for learning Danish grammar, the important point is:

• komme hjem = motion toward home

And in natural English it will often be translated as get home.

Yes, it is natural and grammatical.

A Dane might also say things like:

• Det tager mere end et kvarter at komme hjem, hvis trafikken står stille
• Det tager over et kvarter at komme hjem, hvis trafikken står stille

But your original sentence is perfectly good Danish.

A small nuance is that trafikken står stille suggests traffic is really not moving, so it describes a pretty serious slowdown or standstill, not just ordinary heavy traffic.