Я їду на автобусі, а не на таксі.

Because їду comes from їхати, which means to go / travel by vehicle.

• їхати → їду = I am going / riding / traveling by some transport
• йти → йду = I am going on foot

So in Я їду на автобусі, the speaker is traveling by bus, not walking.

This is a very common question.

• їду usually refers to one trip, often right now or a specific journey
• їжджу usually means I go by vehicle regularly / habitually

So:

• Я їду на автобусі = I’m going by bus
• Я їжджу на автобусі = I go by bus / I usually take the bus

In your sentence, їду fits because it describes a specific trip.

In Ukrainian, one common way to say by bus, by taxi, by train, etc. is to use на + the transport noun.

So:

• на автобусі = by bus
• на таксі = by taxi

This is a normal Ukrainian pattern for transportation. English uses by, but Ukrainian often uses на in these expressions.

Because after на in this meaning, Ukrainian commonly uses the locative case.

• dictionary form: автобус
• locative singular: автобусі

So:

• на автобусі = on/by bus

This is why the ending changes from -ус to -усі.

Because таксі is an indeclinable noun in Ukrainian. That means it usually keeps the same form in all cases.

So you get:

• таксі
• на таксі
• у таксі
• без таксі

The word stays таксі.

а не creates a contrast: but not or rather than.

So the structure is:

• X, а не Y = X, not Y / X rather than Y

In this sentence:

• Я їду на автобусі, а не на таксі = I’m going by bus, not by taxi

The word а signals contrast between the two options.

Not always.

Ukrainian verb forms often already show the person, so їду already means I am going. Because of that, Я can be omitted:

• Їду на автобусі, а не на таксі.

That is still correct.

However, Я may be included for:

• emphasis
• clarity
• contrast
• more explicit speech

So Я їду... is perfectly natural.

Yes. That is also correct.

Ukrainian has more than one way to express means of transport:

• Я їду на автобусі
• Я їду автобусом

The second version uses the instrumental case: автобусом.

Both are natural. Very roughly:

• на автобусі is extremely common in everyday speech
• автобусом is also standard and often feels a bit more compact

A learner should understand both.

Literally, it looks like on the bus, but in this sentence it is best understood as by bus.

This is important because Ukrainian and English do not always match word-for-word.

Compare:

• Я їду на автобусі = I’m going by bus
• Я в автобусі = I’m in the bus / on the bus physically

So in your sentence, на автобусі is about the means of transport, not physical position.

Because а is a coordinating conjunction, and in Ukrainian it is normally separated by a comma when it connects contrasting parts.

So:

• Я їду на автобусі, а не на таксі.

The comma marks the contrast between:

• на автобусі
• не на таксі

This punctuation is standard.

Yes, Ukrainian word order is fairly flexible, though the emphasis may change.

For example:

• Я їду на автобусі, а не на таксі.
• Я їду не на таксі, а на автобусі.

Both are correct, but they focus slightly differently.

• на автобусі, а не на таксі starts with the actual choice first
• не на таксі, а на автобусі first rejects one option, then gives the correct one

A very natural contrastive version is:

• Я їду не на таксі, а на автобусі.

The letter ї is pronounced roughly like yi or yi in yield, though not exactly the same as in English.

So їду is approximately:

• yi-du

A simple learner-friendly guide:

• ї = a sound like y + i
• їду ≈ yi-DOO

Also note that ї is always pronounced clearly; it is not silent.

It is completely normal everyday Ukrainian.

Nothing in the sentence sounds strange, overly formal, or bookish. A native speaker could easily say this in ordinary conversation, for example when explaining how they are traveling:

• to work
• to school
• to another part of town

So this is a very useful real-life sentence pattern to learn.