Когда поезд останавливается, я подхожу к выходу.

Because this sentence normally describes a habitual or repeated situation:

• Когда поезд останавливается, я подхожу к выходу.
• Whenever the train stops, I go up to the exit.

In Russian, the present tense is often used for things that happen regularly or as a general rule.

If you wanted to talk about one specific future occasion, Russian would usually prefer:

• Когда поезд остановится, я подойду к выходу.

That means When the train stops, I’ll go to the exit.

So the present-tense version sounds more like a routine, while the future-perfective version sounds like a single future event.

Когда can mean both when and whenever, depending on context.

In this sentence, because both verbs are in the present tense and the meaning is habitual, когда is understood more like:

• when
• whenever

So:

• Когда поезд останавливается, я подхожу к выходу. = When/Whenever the train stops, I go up to the exit.

Russian often does not separate these two meanings as sharply as English does. The tense and aspect usually make the meaning clear.

Because Когда поезд останавливается is a subordinate clause, and Russian separates subordinate clauses with a comma.

So the structure is:

• Когда поезд останавливается, — subordinate clause
• я подхожу к выходу. — main clause

This comma is required in standard Russian spelling.

You can also reverse the order:

• Я подхожу к выходу, когда поезд останавливается.

That is also correct, and the comma is still needed.

The verb here is останавливаться / остановиться, which means to stop in the sense of come to a stop.

For vehicles like trains, buses, and cars, Russian commonly uses this reflexive form:

• Поезд останавливается. = The train stops / is stopping.

This is just the normal intransitive verb for a train stopping.

Compare:

• останавливать / остановить = to stop something
• останавливаться / остановиться = to stop oneself / to come to a stop

Examples:

• Машинист останавливает поезд. = The driver stops the train.
• Поезд останавливается. = The train stops.

So -ся is not optional here; it is part of the usual verb meaning.

Подхожу comes from подходить / подойти, which means to approach, to come up to, or to move toward and reach something.

So:

• я иду к выходу = I am going to the exit
• я подхожу к выходу = I go up to / approach the exit

Подхожу suggests getting close to the exit, not just moving in that direction.

That makes it a very natural choice here, because the speaker is probably moving toward the door in preparation to get off.

К takes the dative case, so выход becomes выходу.

• dictionary form: выход
• after к: к выходу

So:

• к выходу = to the exit / toward the exit

This phrase shows direction toward a point.

A useful comparison:

• к выходу = toward the exit
• у выхода = by the exit
• из выхода is generally not how you would say out of the exit in normal Russian; instead Russian usually rephrases it.

Выход literally means exit.

In this sentence, it usually refers to:

• the exit area,
• the doors,
• the place where passengers get out.

So я подхожу к выходу means the speaker goes toward the place where people leave the train.

Depending on context, English might translate it as:

• I go to the exit
• I move toward the doors
• I go up to the door

Останавливаться is the imperfective partner of остановиться.

In this sentence, the imperfective present is natural because the sentence describes a repeated pattern:

• Whenever the train stops, I go to the exit.

Russian commonly uses the imperfective present for repeated actions and general behavior.

If you change it to the perfective future:

• Когда поезд остановится, я подойду к выходу.

that refers to one future event, not a repeated habit.

So the choice of aspect helps show the difference between:

• habit/routine → останавливается
• single future completion → остановится

For the same reason: the sentence describes something that happens regularly.

• подходить = imperfective
• подойти = perfective

So:

• я подхожу к выходу = I go up to the exit / I usually approach the exit
• я подойду к выходу = I will go up to the exit or I will approach the exit once

In a habitual sentence, imperfective is the normal choice.

Usually, not naturally. As written, it sounds more like a general rule or repeated action.

A Russian speaker would normally understand:

• Когда поезд останавливается, я подхожу к выходу. as
• Whenever the train stops, I go to the exit.

For a single future event, Russian usually changes both verbs to perfective future:

• Когда поезд остановится, я подойду к выходу.

That is the more natural way to say:

• When the train stops, I’ll go to the exit.

Yes. Russian word order is flexible, although the meaning stays basically the same.

You can say:

• Когда поезд останавливается, я подхожу к выходу.
• Я подхожу к выходу, когда поезд останавливается.

Both are correct.

The version with когда first is often a little more natural when you want to set the situation first: When the train stops...

Russian word order often affects focus and emphasis, not basic grammar.

Yes, it could be omitted in many contexts, because Russian verb endings often show the subject clearly:

• Когда поезд останавливается, подхожу к выходу.

That can work, especially in conversation.

But including я is also completely normal. It can make the sentence clearer, more neutral, or slightly more explicit.

So both are possible:

• ...я подхожу к выходу
• ...подхожу к выходу

Russian often still uses the same sentence, depending on context:

• Когда поезд останавливается, я подхожу к выходу.

This can already suggest the general timing: as the train is coming to a stop, I move toward the exit.

If you want to emphasize the process more strongly, you might use wording like:

• Когда поезд начинает останавливаться, я подхожу к выходу.
• As the train starts slowing to a stop, I go to the exit.

But in ordinary Russian, the original sentence is very natural and does not need to be more explicit.