Tomgangsgebyret er høyt.

Because Norwegian usually writes compound nouns as one word, where English often uses two or more words.

So:

• tomgang = idling / running idle
• gebyr = fee
• tomgangsgebyr = idling fee
• tomgangsgebyret = the idling fee

This is very common in Norwegian. English speakers often want to separate compounds, but in Norwegian they are normally joined.

The ending -et marks the noun as definite singular for a neuter noun.

Here is the pattern:

• et gebyr = a fee
• gebyret = the fee

So:

• et tomgangsgebyr = an idling fee
• tomgangsgebyret = the idling fee

Unlike English, Norwegian often adds the directly onto the noun as an ending.

That -s- is a linking s used in many Norwegian compounds.

So the compound is built like this:

• tomgang
• linking -s-
• gebyr

giving tomgangsgebyr

The -s- does not usually have a separate meaning by itself. It is just a common way of connecting parts of a compound. English learners often notice this because English does not really do the same thing in the same way.

Because the adjective agrees with the noun gebyret, and gebyr is a neuter noun.

With predicate adjectives after er, Norwegian still shows agreement:

• Avgiften er høy. = The charge/fee is high.
  (if the noun is common gender)
• Gebyret er høyt. = The fee is high.
  (because gebyr is neuter)

So the -t in høyt is there because the thing being described is et gebyr, a neuter noun.

The base dictionary form is høy.

Common forms are:

• høy = used with common gender singular nouns
• høyt = used with neuter singular nouns
• høye = plural and often definite forms

Examples:

• en høy pris = a high price
• et høyt gebyr = a high fee
• høye priser = high prices

In your sentence, høyt is correct because gebyr is neuter.

No, this is a very basic Norwegian sentence pattern:

• Tomgangsgebyret = subject
• er = verb
• høyt = adjective / subject complement

So the structure is:

Subject + verb + complement

This is the same basic order as in English:

The idling fee + is + high

Er is the present tense of å være, which means to be.

So:

• jeg er = I am
• du er = you are
• han/hun er = he/she is
• det er = it is
• vi er = we are

In this sentence, er simply means is.

Because in Norwegian, the definite form is often built into the noun itself.

Compare:

• English: the fee
• Norwegian: gebyret

This is one of the first big differences English speakers notice. Norwegian can also use an extra determiner in some cases, especially with adjectives, for example:

• det høye gebyret = the high fee

But in your sentence there is no adjective directly before the noun, so the noun just takes the definite ending:

• tomgangsgebyret

Yes, grammatically you could, but it means something a little different.

• Tomgangsgebyret er høyt. = The idling fee is high.
  This refers to a specific fee.
• Et tomgangsgebyr er høyt. = An idling fee is high.
  This sounds more general or less tied to a specific situation.

So the choice between them depends on whether you mean a specific known fee or just an idling fee in general.

A rough guide is something like hoyt, but with the Norwegian vowel ø, which does not exist in standard English.

A few notes:

• høy has a diphthong somewhat like the vowel movement in English boy, but starting from ø
• the final -t is pronounced in høyt

If you already know Norwegian sounds a bit, think of:

• høy
  • t = høyt

The hardest part for English speakers is usually the ø sound.

Yes, it is a normal and useful word, especially in formal, official, or financial contexts.

It often means fee, charge, or sometimes administrative fee.

Examples:

• et gebyr = a fee
• et parkeringsgebyr = a parking fee / parking penalty, depending on context
• et purregebyr = a reminder fee
• et tomgangsgebyr = an idling fee

So it is a good word to learn if you read signs, rules, bills, or official information.