Umferðarljósin við skólann virka ekki í morgun.

The ending -in is the definite article, attached to the noun itself. So:

• umferðarljós = traffic lights / a traffic light (indefinite, depending on context)
• umferðarljósin = the traffic lights

In Icelandic, the word for the is usually added to the end of the noun instead of written as a separate word.

It can be a little confusing because ljós has the same basic form in both singular and plural in some cases.

Here, umferðarljósin is plural definite: the traffic lights.

Related forms:

• umferðarljós = a traffic light or traffic lights (indefinite, depending on context)
• umferðarljósið = the traffic light (singular definite)
• umferðarljósin = the traffic lights (plural definite)

So in this sentence, the meaning is definitely plural.

It is a compound word:

• umferð = traffic
• ljós = light

So umferðarljós literally means traffic light(s).

Compound nouns are very common in Icelandic, and English speakers often need a little time to get used to reading them as one word.

Because við is a preposition, and it requires the noun after it to be in the accusative case here.

The noun is:

• nominative: skólinn = the school
• accusative: skólann = the school as an object / after certain prepositions

So:

• við skólann = by the school / near the school

This is a very common thing in Icelandic: prepositions often control a specific case.

Here við means by, near, or at in the sense of location.

So við skólann means:

• by the school
• near the school
• at the school (in the sense of being next to it, not inside it)

It does not mean with here, even though við can sometimes look confusing to learners because prepositions do not always match English one-to-one.

Virka means to work, to function, or to be working.

So:

• virka = work / function
• virka ekki = not work / not be working

This is a very natural verb for machines, devices, systems, traffic lights, phones, computers, and so on.

Examples:

• Síminn virkar ekki. = The phone isn’t working.
• Ljósin virka ekki. = The lights aren’t working.

Ekki means not, and in a simple sentence like this it usually comes after the finite verb.

So:

• Umferðarljósin virka ekki = The traffic lights are not working

This is normal Icelandic word order.

Compare:

• Hann kemur ekki. = He is not coming.
• Ég skil ekki. = I do not understand.

So English speakers should get used to seeing not after the verb much of the time.

Í morgun means this morning.

This is an idiomatic time expression in Icelandic.

So:

• í morgun = this morning
• í dag = today
• í kvöld = this evening / tonight

Even though í often means in, you should learn í morgun as a fixed expression meaning this morning.

This is a very important distinction:

• í morgun = this morning / earlier today in the morning
• á morgun = tomorrow

So the sentence means the traffic lights are not working this morning, not tomorrow.

This is a very common thing for learners to mix up, so it is worth memorizing early.

Because Icelandic often uses a simple lexical verb where English uses be + -ing.

Here:

• virka ekki = do not work / are not working

Icelandic does have ways to express ongoing action, but very often the simple present tense covers what English would express with either:

• work
• are working

So virka ekki í morgun naturally means aren’t working this morning.

It is present tense.

The basic idea is:

• virka = work / are working

Because of the time phrase í morgun, the sentence is understood as referring to the present situation this morning.

So even though English uses are not working, Icelandic simply uses the present tense form virka.

Not this exact Icelandic sentence, because umferðarljósin is plural definite: the traffic lights.

If you wanted singular definite, you would expect:

• umferðarljósið

So this sentence specifically refers to the traffic lights, not the traffic light.

Yes. Icelandic usually follows the verb-second pattern, which means the finite verb tends to stay in the second position.

So you can say:

• Umferðarljósin við skólann virka ekki í morgun.
• Í morgun virka umferðarljósin við skólann ekki.

When Í morgun comes first, the verb virka comes next.

That is a very common Icelandic pattern and an important one to notice.

Yes. It specifies which traffic lights:

• umferðarljósin = the traffic lights
• við skólann = by the school

Together:

• umferðarljósin við skólann = the traffic lights by the school

So this phrase narrows down the reference to a particular set of traffic lights.

A learner should especially notice these:

• Definite article attached to the noun
  umferðarljósin = the traffic lights

• Preposition + case
  við takes accusative here, so skólann

• Negation after the verb
  virka ekki

• Idiomatic time expression
  í morgun = this morning

• Simple present used naturally
  virka ekki = are not working

This is actually a very useful everyday sentence because it shows several basic Icelandic patterns at once.