Við göngum á gangstéttinni þegar umferðin er mikil.

Við means we, and göngum is the 1st person plural form of the verb að ganga (to walk).

Icelandic often allows the subject pronoun to be included for clarity or emphasis, and in a normal learner sentence like this, Við göngum is the standard way to say we walk or we are walking.

• við = we
• göngum = walk / are walking

So Við göngum means we walk.

Göngum comes from the verb að ganga, which means to walk, to go on foot, and in some contexts to go.

The dictionary form is the infinitive: ganga.
But in the sentence, the verb is conjugated to match we:

• ég geng = I walk
• þú gengur = you walk
• hann/hún/það gengur = he/she/it walks
• við göngum = we walk
• þið gangið = you all walk
• þeir/þær/þau ganga = they walk

The vowel changes are normal in Icelandic verb conjugation, so ganga becoming göngum is something you just learn as part of the verb pattern.

Because after á in this sentence, gangstétt is in the dative singular definite form.

Breakdown:

• gangstétt = sidewalk / pavement
• gangstéttin = the sidewalk (nominative singular definite)
• gangstéttinni = on the sidewalk (dative singular definite)

Here á means on, and when it describes being in a location rather than movement onto something, it usually takes the dative.

So:

• á gangstéttinni = on the sidewalk

This is a very common Icelandic pattern:

• á + dative for location
• á + accusative for motion onto something

In Icelandic, some prepositions can take different cases depending on meaning. Á is one of them.

A very useful rule is:

• location / position → usually dative
• motion toward / onto → usually accusative

In this sentence, the idea is that we are walking on the sidewalk, meaning our location is on it. That gives:

• á gangstéttinni = on the sidewalk

Compare:

• Við erum á gangstéttinni. = We are on the sidewalk.
• Við göngum á gangstéttina. = We walk onto the sidewalk.

So here it is dative because the sidewalk is the place where the action happens.

The -inni ending shows two things at once:

1. the noun is definite = the sidewalk
2. the noun is in the dative singular

Icelandic usually adds the as a suffix to the noun instead of using a separate word like English the.

So:

• gangstétt = sidewalk
• gangstéttin = the sidewalk
• gangstéttinni = to/on/from the sidewalk, depending on the preposition or context

The exact ending depends on the noun’s gender, number, and case.

Þegar means when here. It introduces a subordinate clause:

• þegar umferðin er mikil = when the traffic is heavy

So the whole sentence has two parts:

• Við göngum á gangstéttinni
• þegar umferðin er mikil

Together, the second part explains under what circumstances we walk on the sidewalk.

A useful thing to know is that þegar can also refer to time in other contexts, such as when in past or future situations.

Umferð means traffic.
Umferðin means the traffic.

In this sentence, Icelandic uses the definite form, which is very natural when talking about traffic in a general real-world situation:

• umferð = traffic
• umferðin = the traffic

Just like with gangstéttinni, Icelandic adds the definite article to the end of the noun.

Because mikil has to agree with umferðin.

The noun umferð is:

• feminine
• singular
• here it is in the nominative

So the adjective must match it:

• mikill = masculine singular nominative
• mikil = feminine singular nominative
• mikið = neuter singular nominative/accusative

Since umferðin is feminine singular, the correct form is:

• umferðin er mikil = the traffic is heavy

This kind of adjective agreement is very important in Icelandic.

Not exactly. The basic meaning of mikill / mikil / mikið is more like big, great, much, or large in amount. But in context, it often corresponds to natural English translations like heavy.

So:

• umferðin er mikil literally means something like the traffic is great/large
• natural English: the traffic is heavy

This is a good example of how Icelandic and English use different adjective choices in idiomatic expressions.

Because in Icelandic subordinate clauses introduced by words like þegar, the normal word order places the verb after the subject:

• þegar umferðin er mikil

That is:

• þegar = when
• umferðin = the traffic
• er = is
• mikil = heavy

In main clauses, Icelandic often follows a verb-second pattern, but subordinate clauses usually do not. So this sentence shows a very useful contrast:

• main clause: Við göngum ...
• subordinate clause: þegar umferðin er mikil

Yes. Er is the present singular form of að vera (to be).

Here it agrees with umferðin, which is singular:

• umferðin er mikil = the traffic is heavy

Some common present forms of að vera are:

• ég er = I am
• þú ert = you are
• hann/hún/það er = he/she/it is
• við erum = we are
• þið eruð = you are
• þeir/þær/þau eru = they are

It can mean either, depending on context.

Icelandic often uses the simple present where English may use either:

• we walk
• we are walking

So Við göngum á gangstéttinni þegar umferðin er mikil could describe:

• a habitual action: We walk on the sidewalk when traffic is heavy
• or, in some contexts, a present action

Usually, without extra context, learners should read it as a general statement or habit.

Yes. Að ganga is a very common Icelandic verb with several related meanings depending on context. It can mean:

• to walk
• to go on foot
• sometimes more broadly to go
• in other contexts, it can even mean things like to function, to proceed, or to be happening

But in this sentence, because of á gangstéttinni (on the sidewalk), the meaning is clearly to walk.

Most naturally, it sounds like a general or habitual statement:

• We walk on the sidewalk when traffic is heavy.

That means this is something people do under those circumstances, not necessarily something happening only once.

If Icelandic wanted to make the moment more specific, it would usually rely on extra context, time expressions, or a different construction.

Yes, you could, but it changes the feel slightly.

• á gangstéttinni = on the sidewalk
• á gangstétt = on a sidewalk / on sidewalk, depending on context

Using the definite form gangstéttinni sounds more like referring to the sidewalk as the normal, known place where one walks. That is very natural in a sentence like this.

Using the indefinite form might sound more general or less specific, but the definite form is very idiomatic here.

Here is the case breakdown:

• Við = nominative, because it is the subject
• gangstéttinni = dative, because it follows á in a location sense
• umferðin = nominative, because it is the subject of er

So structurally:

• Við — subject of göngum
• á gangstéttinni — prepositional phrase
• umferðin — subject of er
• mikil — adjective agreeing with umferðin

The sentence has:

1. a main clause

   • Við göngum á gangstéttinni
   • We walk on the sidewalk

2. a subordinate clause introduced by þegar

   • þegar umferðin er mikil
   • when the traffic is heavy

So the pattern is:

[main clause] + [þegar + subordinate clause]

This is a very common and useful sentence structure in Icelandic.