Alternativ fahren wir mit dem Bus.

Because German main clauses normally follow the verb-second rule: the finite verb goes in the second position.

In this sentence, Alternativ is placed first, so the verb fahren must come next:

• Alternativ fahren wir mit dem Bus.

If the subject comes first, then you get:

• Wir fahren alternativ mit dem Bus.

That version is grammatically possible, but it sounds a bit different and is less natural in many contexts. With Alternativ at the front, the sentence clearly connects to a previous option: As an alternative, we go by bus.

Here, alternativ is being used adverbially. It describes the whole idea of the sentence, not a noun.

So it means something like:

• alternatively
• as an alternative

Compare:

• eine alternative Lösung = an alternative solution
  
  • here alternative is an adjective
• Alternativ fahren wir mit dem Bus.
  
  • here alternativ works like an adverb

A small spelling note: since it is the first word in the sentence, it is capitalized. In the middle of a sentence, it would normally be lowercase:

• Wir fahren alternativ mit dem Bus.

It is understandable, but many native speakers would more naturally say something like:

• Alternativ können wir mit dem Bus fahren.
• Stattdessen fahren wir mit dem Bus.
• Als Alternative fahren wir mit dem Bus.

Why? Because bare alternativ at the beginning of a sentence can sound a little formal, written, or slightly unusual depending on context.

So the sentence is useful for learning grammar, but in everyday conversation, Germans may prefer stattdessen or a fuller phrase like als Alternative.

Because fahren is the usual verb for travelling by vehicle.

• fahren = go/travel/ride/drive by some means of transport
• gehen = go on foot, walk

So:

• Wir fahren mit dem Bus. = We go by bus.
• Wir gehen. = We go on foot / We walk.

English uses go in both cases, but German often makes the difference more clearly.

Yes. Wir nehmen den Bus is very common and natural.

There is a slight difference in focus:

• Wir fahren mit dem Bus.
  Focuses on the means of transport we are using.
• Wir nehmen den Bus.
  Focuses more on the choice of taking the bus.

Both can often work in similar situations.

Because the preposition mit always takes the dative case.

The noun Bus is masculine:

• nominative: der Bus
• dative: dem Bus

So:

• mit dem Bus
• mit dem Auto
• mit dem Zug

This is a very common pattern in German.

That is simply how German normally expresses this idea.

English often says:

• by bus
• by train
• by car

German usually says:

• mit dem Bus
• mit dem Zug
• mit dem Auto

So even though English has no article here, German usually does.

There are other possible expressions, such as per Bus, but mit dem Bus is the most common everyday version.

Yes, it is grammatically correct, but the emphasis changes.

• Alternativ fahren wir mit dem Bus.
  The sentence begins with the idea of an alternative. This strongly links it to a previous suggestion.
• Wir fahren alternativ mit dem Bus.
  This sounds less natural in many everyday situations. It can feel like alternatively is attached later and is not as smoothly connected.

In real conversation, if the subject comes first, people often prefer:

• Wir fahren stattdessen mit dem Bus.
• Wir können alternativ mit dem Bus fahren.

Yes. The noun is:

• der Bus

So the forms are:

• nominative: der Bus
• accusative: den Bus
• dative: dem Bus
• genitive: des Busses

That is why this sentence has dem Bus after mit.

The basic word order would be:

• Wir fahren mit dem Bus.

That is the neutral structure:

1. subject: wir
2. verb: fahren
3. rest of the sentence: mit dem Bus

When you move Alternativ to the first position, German still keeps the finite verb in second position:

• Alternativ fahren wir mit dem Bus.

So the subject moves behind the verb. This is one of the most important German word-order patterns to get used to.