Jeg går altid over vejen ved fodgængerfeltet, når trafikken er tæt.

In Danish main clauses, the finite verb usually comes in second position. This is often called the V2 rule.

So in Jeg går altid over vejen ...:

• Jeg = subject
• går = finite verb
• altid = adverb

That is why går comes before altid.

A rough pattern is:

• Subject + finite verb + adverb + rest

Examples:

• Jeg kommer ofte her. = I often come here.
• Hun spiser aldrig kød. = She never eats meat.

So Jeg altid går sounds wrong in normal Danish word order.

Literally, går over vejen means walks over/across the road.

• går = walk / go on foot
• over = over / across
• vejen = the road

In natural English, you would usually translate it as cross the road rather than walk over the road.

So Danish often uses:

• gå over vejen = cross the road
• gå over gaden = cross the street

Vejen is the definite form of vej:

• en vej = a road
• vejen = the road

In Danish, the definite article is often attached to the end of the noun:

• bil → bilen
• gade → gaden
• vej → vejen

Here, vejen refers to the road being crossed in the situation, so the road is more natural than a road.

In this sentence, ved means at or by:

• ved fodgængerfeltet = at the pedestrian crossing / by the crosswalk

It shows the place where the action happens.

Why not i?

• i usually means in
• A crossing is not something you are really inside

Why not på?

• på can mean on, and in some contexts Danish does use it with places or surfaces
• But with fodgængerfelt, ved is the normal choice when you mean at the crossing

So ved fodgængerfeltet is the natural expression.

Fodgængerfeltet is a compound noun, which is very common in Danish.

It consists of:

• fodgænger = pedestrian
• felt = field, marked area, lane-like area
• -et = the definite ending for a neuter noun

So:

• et fodgængerfelt = a pedestrian crossing / a crosswalk
• fodgængerfeltet = the pedestrian crossing / the crosswalk

Danish often builds long nouns this way:

• togstation = train station
• cykelsti = bike lane
• fodboldbane = football field

Når is used for something that happens whenever, when, or under a general condition. It is often used for repeated situations or general truths.

Here the meaning is something like:

• when traffic is heavy
• whenever traffic is dense/heavy

So når fits because this is a general habit.

Da is more often used for:

• a specific moment in the past
• when in the sense of at the time when

Examples:

• Når jeg er træt, går jeg tidligt i seng. = When I am tired, I go to bed early.
• Da jeg var barn, boede jeg i Odense. = When I was a child, I lived in Odense.

So in your sentence, når is the correct choice.

Literally, trafikken er tæt means the traffic is dense.

In natural English, this usually becomes:

• traffic is heavy
• there is a lot of traffic

So:

• tæt trafik = heavy traffic / dense traffic

Tæt often means:

• close
• dense
• thick
• packed

Examples:

• tæt skov = dense forest
• tæt tåge = thick fog
• tæt trafik = heavy traffic

Both forms can exist, but they are used a little differently.

• trafik = traffic in a general sense
• trafikken = the traffic, meaning the traffic in the situation being discussed

In your sentence, trafikken er tæt refers to the traffic around the speaker at that time or in that context, so the definite form sounds natural.

Compare:

• Der er meget trafik i København. = There is a lot of traffic in Copenhagen.
• Trafikken er tæt i morges. = The traffic is heavy this morning.

Yes. You can also say:

Når trafikken er tæt, går jeg altid over vejen ved fodgængerfeltet.

That means the same thing.

But notice what happens in the main clause after the subordinate clause: Danish keeps the verb in second position, so you get:

• Når trafikken er tæt, går jeg ... not
• Når trafikken er tæt, jeg går ...

This inversion is very important in Danish word order.

Because går is not an infinitive here. It is a present tense finite verb.

• at gå = to walk / to go on foot
• jeg går = I walk / I am walking

Danish uses at for the infinitive:

• Jeg kan lide at gå. = I like to walk.

But in your sentence, the verb is the main action of the clause, so it appears as:

• Jeg går ...

Gå often means walk, but it can also mean go in contexts where movement on foot is understood.

In this sentence, because of over vejen and ved fodgængerfeltet, the idea is clearly walking across the road, so walk/cross is the best sense.

Compare:

• Jeg går hjem. = I walk home / I go home on foot.
• Vi går til skole. = We walk to school.
• Hvordan går det? = How are things going?

So gå is a very flexible verb, but here it is definitely about going on foot.

Sometimes adverbs can move for emphasis, but altid normally appears after the finite verb in a main clause like this:

• Jeg går altid over vejen ...

That is the most neutral and natural order.

If another element comes first, the verb still stays second:

• Ved fodgængerfeltet går jeg altid over vejen ...

But this sounds more marked, because now ved fodgængerfeltet is being emphasized.

For a learner, the safest default is:

• Subject + finite verb + altid + rest

Usually yes, in everyday meaning.

• fodgængerfelt = pedestrian crossing / crosswalk
• In British English, this may often be called a zebra crossing, depending on the exact type of crossing.
• In American English, crosswalk is usually the best match.

So the Danish word is broader and corresponds most safely to pedestrian crossing or crosswalk.