Bevor wir auf die Autobahn fahren, müssen wir noch tanken.

Because bevor introduces a subordinate clause. In German, the conjugated verb usually goes to the end of a subordinate clause.

So:

• Bevor = subordinating conjunction
• wir = subject
• auf die Autobahn = prepositional phrase
• fahren = verb, placed at the end

This is a very common pattern:

• bevor wir gehen
• weil er müde ist
• dass sie kommt

So Bevor wir auf die Autobahn fahren follows normal German subordinate-clause word order.

Because in German, a subordinate clause is normally separated from the main clause by a comma.

Here the sentence has:

• subordinate clause: Bevor wir auf die Autobahn fahren
• main clause: müssen wir noch tanken

So the comma is required:

Bevor wir auf die Autobahn fahren, müssen wir noch tanken.

This is one of the most important punctuation rules in German.

Because the sentence begins with the subordinate clause. In German main clauses, the conjugated verb must be in position 2.

The whole first clause counts as position 1:

• Bevor wir auf die Autobahn fahren = position 1
• müssen = position 2
• wir = then comes the subject

So:

• Bevor wir auf die Autobahn fahren, müssen wir noch tanken.

If you put the main clause first, then you get the more familiar order:

• Wir müssen noch tanken, bevor wir auf die Autobahn fahren.

Both are correct.

Because müssen is a modal verb. With modal verbs in German, the second verb usually stays in the infinitive and goes to the end of the clause.

So:

• müssen = conjugated modal verb
• tanken = infinitive at the end

This is the same pattern as:

• Ich muss arbeiten.
• Wir können kommen.
• Sie will schlafen.

So müssen wir noch tanken is completely regular.

Because after a modal verb like müssen, German does not use zu.

So you say:

• Wir müssen tanken.
• Ich kann kommen.
• Sie will gehen.

Not:

• Wir müssen zu tanken. ❌

Some other structures do use zu, but modal verbs normally do not.

Because this sentence expresses movement toward/onto the Autobahn, not location.

German often uses different cases depending on whether you mean:

• location = where something is
• direction/movement = where something is going

With auf:

• auf der Autobahn = on the Autobahn, located there
• auf die Autobahn fahren = to drive onto the Autobahn

Here the idea is entering or moving onto it, so German uses the accusative:

• die Autobahn

This is a very common two-way preposition pattern.

Here noch means something like still, yet, or one more thing before that.

In this sentence, it gives the idea:

• before we go onto the Autobahn, we still need to refuel
• refueling is something that has to happen first

So noch adds a nuance of “before that happens, there is still this remaining thing to do.”

Without noch, the sentence is still grammatical:

• Bevor wir auf die Autobahn fahren, müssen wir tanken.

But noch makes it sound more natural and adds the idea that this is a remaining task.

Tanken means to refuel / to fill up with fuel / to get gas.

For cars, English often says:

• get gas
• fill up
• refuel

German uses tanken very naturally in this context.

Related words:

• die Tankstelle = gas station / petrol station
• volltanken = fill up completely

So in this sentence, tanken refers to putting fuel in the car before driving on the Autobahn.

Usually yes, when it connects two actions or events.

Examples:

• Bevor ich gehe, rufe ich dich an.
• Bevor wir essen, waschen wir uns die Hände.

A useful rule:

• bevor = before as a conjunction introducing a clause
• vor = before/in front of as a preposition

Compare:

• Bevor wir fahren, tanken wir. = Before we drive, we refuel.
• Vor der Fahrt tanken wir. = Before the trip, we refuel.

So bevor is the right choice here because it introduces a full clause: wir auf die Autobahn fahren.

Yes, absolutely. That version is very natural too.

Compare:

• Bevor wir auf die Autobahn fahren, müssen wir noch tanken.
• Wir müssen noch tanken, bevor wir auf die Autobahn fahren.

The meaning is basically the same. The difference is mainly focus:

• starting with Bevor... emphasizes the time relationship first
• starting with Wir müssen... emphasizes the obligation first

Both are good standard German.

In this sentence, fahren most naturally means to drive/go by vehicle, since the context is a car and the Autobahn.

German fahren is often used for traveling by vehicle, not only when you yourself are literally the driver.

So depending on context, fahren can correspond to:

• drive
• go
• travel

But with Autobahn and tanken, the car-related meaning is especially clear.