Ik ga ervan uit dat we op tijd zullen vertrekken, maar ik houd er toch rekening mee dat het in de vertrekhal druk kan zijn.

Ervan uitgaan is a fixed Dutch expression meaning to assume or to proceed on the assumption.

It is built from:

• uitgaan van = to be based on / to start from
• ervan uitgaan = to assume it, to take it for granted

In this sentence, ervan points forward to the whole dat clause:

• Ik ga ervan uit dat we op tijd zullen vertrekken
• literally: I go from it out that...
• natural English: I assume that we will leave on time

This kind of er + preposition combination is very common in Dutch.

Because uitgaan is a separable verb.

In a main clause, the verb splits:

• Ik ga ... uit

The other part, ervan, stays together because it functions as a pronominal adverb.

So:

• Ik ga ervan uit dat... = correct

Compare:

• infinitive: ervan uitgaan
• main clause: ik ga ervan uit
• subordinate clause: dat ik ervan uitga

This split is normal for separable verbs in Dutch.

The dat introduces the content of the assumption.

So:

• Ik ga ervan uit dat... = I assume that...

Dutch often uses dat after verbs and expressions that introduce thoughts, assumptions, statements, or expectations.

Examples:

• Ik denk dat... = I think that...
• Ik hoop dat... = I hope that...
• Ik ga ervan uit dat... = I assume that...

Zullen vertrekken expresses the future: will leave / will depart.

So:

• we vertrekken = we leave / we are leaving
• we zullen vertrekken = we will leave

Dutch often uses the present tense for future meaning, so we vertrekken op tijd could also be possible in many contexts. But zullen vertrekken makes the future idea more explicit.

In this sentence, it sounds slightly more formal or deliberate:

• Ik ga ervan uit dat we op tijd zullen vertrekken

After dat, Dutch uses subordinate-clause word order, which pushes the verbs to the end.

So:

• main clause: We zullen op tijd vertrekken
• subordinate clause: dat we op tijd zullen vertrekken

Structure:

• dat
  • subject + other elements + verbs at the end

Here:

• dat = that
• we = subject
• op tijd = on time
• zullen vertrekken = verb cluster at the end

Op tijd usually means on time, meaning not late.

So:

• op tijd vertrekken = leave on time

It is not always the same as English in time. English in time often means early enough before something happens.

Dutch distinction:

• op tijd = on time, punctually
• op tijd voor... can sometimes overlap with in time for...

In this sentence, the basic sense is clearly:

• we will depart on time
• not: we will depart early enough for something else

Rekening houden met means to take into account or to keep in mind.

When the thing being referred to is not a noun but a clause or general idea, Dutch often uses a pronominal adverb:

• met iets rekening houden = to take something into account
• er rekening mee houden dat... = to take into account that...

So:

• ik houd er rekening mee dat het ... druk kan zijn
• natural English: I do take into account that it may be busy...

Again, the er points forward to the dat clause.

Mee is the form of met used inside a pronominal adverb.

Dutch often combines:

• er + preposition
  into forms like:
• eraan = at/on it
• ervoor = for it
• ervan = of/from it
• ermee = with it

Because the expression is rekening houden met, the met becomes mee in this construction:

• ik houd rekening met het weer
• ik houd er rekening mee dat het kan regenen

So mee is there because of met.

Toch is hard to translate with just one English word. Here it adds a sense like:

• still
• nevertheless
• all the same
• even so

The sentence contrasts two ideas:

• I assume we will leave on time,
• but I still take into account that it may be busy in the departure hall.

So toch strengthens the contrast:

• maar ik houd er toch rekening mee...
• but I still take into account...

It suggests: even though I expect things to go well, I am still being cautious.

Because this is another subordinate clause introduced by dat:

• dat het in de vertrekhal druk kan zijn

In subordinate clauses, the verbs go to the end.

Here:

• het = dummy subject, like English it
• in de vertrekhal = in the departure hall
• druk = busy
• kan zijn = can be / may be

So the structure is:

• dat
  • subject + place + predicate + verbs at the end

This is very typical Dutch subordinate-clause word order.

The het here works like English it in:

• it may be busy in the departure hall

It does not refer to a specific object. It is a dummy subject needed by the sentence structure.

Compare:

• Het is druk = It is busy
• Het kan druk zijn = It can be busy

So in:

• dat het in de vertrekhal druk kan zijn the het is simply the grammatical subject.

Here druk means busy or crowded.

In:

• het kan druk zijn druk is a predicate adjective, used after zijn.

Predicate adjectives do not take the extra -e ending:

• de drukke straat = the busy street
• de vertrekhal is druk = the departure hall is busy

So druk stays plain because it comes after the verb, not before a noun.

Vertrekhal is a compound noun:

• vertrek = departure
• hal = hall

So de vertrekhal means the departure hall, especially in an airport or major station context.

Dutch forms many nouns by combining smaller words like this.

Both ik houd and ik hou exist in modern Dutch.

• ik houd is often seen as slightly more formal or careful in writing
• ik hou is very common in everyday language

So:

• ik houd er rekening mee = fully correct
• ik hou er rekening mee = also common and correct in many contexts

In a more neutral or written sentence like this one, houd is very natural.

Yes, but the tone would change.

For example:

• Ik denk dat we op tijd zullen vertrekken instead of Ik ga ervan uit dat...
• maar ik verwacht wel dat het in de vertrekhal druk kan zijn or maar ik houd wel rekening met drukte...

However, the original sentence is nice because it shows two specific nuances:

• ervan uitgaan dat = to assume
• rekening houden met / ermee dat = to take into account

These are very common and useful expressions in Dutch.