Obwohl das Tempolimit hier niedrig ist, fährt der Mann hinter uns zu schnell.

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

So:

• das Tempolimit ist hier niedrig = normal main-clause order
• obwohl das Tempolimit hier niedrig ist = subordinate-clause order, with ist at the end

This is one of the most important word-order patterns in German.

German main clauses follow the verb-second rule. The finite verb must come in the second position.

Here, the whole subordinate clause Obwohl das Tempolimit hier niedrig ist takes the first position. That means the main clause must begin with the verb:

• Obwohl ..., fährt der Mann hinter uns zu schnell.

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

• Der Mann hinter uns fährt zu schnell, obwohl das Tempolimit hier niedrig ist.

So fährt comes before der Mann because the subordinate clause is occupying position 1.

Obwohl means although, even though, or though.

It introduces a contrast:

• Obwohl das Tempolimit hier niedrig ist = Although the speed limit here is low
• ..., fährt der Mann hinter uns zu schnell = ..., the man behind us is driving too fast

So the idea is: even though the speed limit is already low, he is still going too fast.

Because Tempolimit is a neuter noun, so its article is das.

Like all German nouns, it has a grammatical gender that you simply have to learn with the word:

• das Tempolimit = the speed limit

Also, in this sentence it is the subject of the subordinate clause, so das is nominative singular.

Because niedrig comes after sein and is being used as a predicate adjective.

In German, adjectives are:

• inflected when they come before a noun
• not inflected when they come after verbs like sein, werden, or bleiben

Compare:

• ein niedriges Tempolimit = a low speed limit
• das Tempolimit ist niedrig = the speed limit is low

So niedrig stays in its basic form here.

Schnell means fast.

Zu schnell means too fast.

So:

• Er fährt schnell. = He is driving fast.
• Er fährt zu schnell. = He is driving too fast.

The word zu here adds the idea that the speed is excessive or more than it should be.

Because after a preposition like hinter, you need an object form, not the subject form wir.

• wir = we
• uns = us

So:

• hinter uns = behind us

Also, hinter is a two-way preposition. It can take either:

• dative for location
• accusative for direction

Here it describes location/position: the man is behind us, so that is the location meaning.

A useful detail: for uns, the accusative and dative forms are the same, so the form itself does not change.

Literally, it means the man behind us.

But in context, because the sentence is about a speed limit and someone driving too fast, it naturally means the man in the vehicle behind us or the driver behind us.

German often leaves that kind of context implied, just as English does.

Because German uses a comma to separate a subordinate clause from a main clause.

So in this sentence:

• Obwohl das Tempolimit hier niedrig ist, = subordinate clause
• fährt der Mann hinter uns zu schnell. = main clause

This comma is required in standard German.

Yes. A very natural alternative is:

• Der Mann hinter uns fährt zu schnell, obwohl das Tempolimit hier niedrig ist.

The meaning stays basically the same.

The main difference is the word order:

• If the obwohl clause comes first, the main clause starts with the verb: fährt
• If the main clause comes first, you get normal subject-verb order: der Mann ... fährt

Both versions are correct.

Yes, fährt is the present tense of fahren.

German present tense often covers both English meanings:

• he drives
• he is driving

In this sentence, because of the context, English would usually say:

• the man behind us is driving too fast

So German uses the simple present, but English may prefer the progressive form.

Hier means here, and it modifies the whole situation: the speed limit is low here, in this place.

German often places adverbs like hier before the adjective or other information they modify:

• das Tempolimit ist hier niedrig = the speed limit is low here

You could also think of it as:

• here = location
• niedrig = description

So the sentence first tells you where, then what it is like.