De trein rijdt vijftig kilometer.

Because trein is a de-word in Dutch. Nouns in Dutch take either de or het as their definite article, and trein belongs to the de group.

So:

• de trein = the train
• not het trein

This is something you usually have to learn with the noun.

Rijdt is the third-person singular present tense of rijden.

• rijden = to drive / to ride / to travel by vehicle
• de trein rijdt = the train travels / runs / is going

In Dutch, rijden is commonly used for vehicles moving on wheels or along a route, including cars, buses, and trains. So even though in English we do not usually say the train drives, Dutch does use rijden here.

Because the subject is de trein, which is third person singular: it.

In the present tense, Dutch usually adds -t for third-person singular verbs:

• ik rijd = I drive / travel
• jij rijdt = you drive / travel
• de trein rijdt = the train drives / travels

So rijdt is the correct form with de trein.

This is a very common question. The infinitive is rijden. The stem is rijd. Then for third-person singular present tense, you add -t:

• stem: rijd
• • t
• = rijdt

In pronunciation, the final d is usually not clearly heard, so rijdt can sound almost like rijt, but the spelling still follows the grammar.

Because Dutch main clauses follow the V2 rule: the finite verb usually comes in the second position.

In this sentence:

• De trein = first element
• rijdt = finite verb, so it comes second
• vijftig kilometer = the rest of the sentence

So the structure is:

• De trein | rijdt | vijftig kilometer

This is normal Dutch word order for a simple statement.

In Dutch, units of measure usually stay in the singular form after a number.

So you say:

• vijftig kilometer
• tien euro
• drie uur

not:

• vijftig kilometers
• tien euros
• drie uren in this kind of measurement use

This is different from English, where we normally say fifty kilometers.

By itself, vijftig kilometer normally refers to a distance: the train travels fifty kilometers.

If you want to express speed, Dutch usually says:

• De trein rijdt vijftig kilometer per uur.
• = The train travels at fifty kilometers per hour.

So without per uur, learners should usually understand it as a distance, not a speed.

No. Dutch can use a bare measure phrase directly after certain verbs, especially verbs of movement.

So:

• De trein rijdt vijftig kilometer.

works without a preposition and means that the train covers that distance.

English can do something similar in sentences like The car went fifty miles, so the idea is not completely foreign, but Dutch uses this structure very naturally.

Usually, rijdt is better here.

Gaan means to go, and it is very common in Dutch, but when talking about a vehicle moving or running, rijden is often the more natural choice.

So:

• De trein rijdt vijftig kilometer. = natural for the vehicle traveling that distance
• De trein gaat ... is possible in some contexts, but it is not the best default choice here

For a learner, rijden is the safer verb with trains in this kind of sentence.

Normally, the most direct reading is that the train travels fifty kilometers.

If you want to say that a route or line has a length of fifty kilometers, Dutch would more often use a different structure, such as:

• De spoorlijn is vijftig kilometer lang.
• Het traject is vijftig kilometer lang.

So De trein rijdt vijftig kilometer is mainly about movement, not the length of the railway itself.