El metro llega al andén cada cuatro minutos.

Because al is the mandatory contraction of a + el in Spanish.

• llegar a = to arrive at
• el andén = the platform

So:

• llega a el andén → llega al andén

This contraction happens whenever a is followed by the masculine singular article el, except when el is part of a proper name, such as a El Escorial.

Because the subject is singular: El metro.

So the verb must also be singular:

• El metro llega = The metro arrives

If the subject were plural, you would use llegan:

• Los trenes llegan al andén cada cuatro minutos = The trains arrive at the platform every four minutes

Spanish often uses the present tense to talk about regular schedules, routines, and repeated events, just like English does.

So El metro llega al andén cada cuatro minutos means that this is what normally happens.

This is sometimes called the habitual present or gnomic present in grammar terms, but in practice it is just the normal present tense used for repeated actions.

It can mean either, depending on context.

In this sentence, el metro most naturally refers to a metro train, because something is arriving at the platform.

So although el metro can also mean the subway/metro system in general, here the context points to the train.

The written accent shows where the stress falls: an-DÉN.

Without the accent, Spanish spelling rules would suggest a different stress pattern. The accent mark tells you that the final syllable is stressed.

Also note the plural:

• andén → andenes

The accent disappears in the plural because the stress pattern changes naturally according to Spanish spelling rules.

In Spain, andén means platform at a train, metro, or railway station.

So:

• estación = station
• andén = platform

They are not the same thing.

• El metro llega a la estación = The metro arrives at the station
• El metro llega al andén = The metro arrives at the platform

The second one is more specific.

Because cada is the normal word for every/each in expressions of frequency.

So:

• cada cuatro minutos = every four minutes

Using todos cuatro minutos is not correct Spanish.

You can also sometimes hear:

• cada 4 minutos
• cada cuatro min.

But cada cuatro minutos is the standard full form.

Because the number is cuatro.

In Spanish, nouns after numbers greater than one are normally plural:

• un minuto
• dos minutos
• cuatro minutos

So cada cuatro minutos is exactly what you would expect grammatically.

Because llegar focuses on arrival at a destination, while venir means to come toward the speaker or toward a reference point.

Here the important idea is that the metro arrives at the platform, so llegar is the natural verb.

Compare:

• El metro llega al andén = The metro arrives at the platform
• El metro viene = The metro is coming

Both can be possible in some contexts, but they express slightly different ideas.

Spanish uses definite articles more often than English does.

Here:

• el metro = the metro / the metro train
• el andén = the platform

In this kind of sentence, the article sounds natural because we are talking about a known or understood metro service and platform situation.

Also, both nouns are masculine singular, so they take el.

Yes, it is natural and correct in Spain.

That said, native speakers might also say things like:

• El metro pasa cada cuatro minutos = The metro comes by every four minutes
• Hay un metro cada cuatro minutos = There is a metro every four minutes
• El tren llega al andén cada cuatro minutos = The train arrives at the platform every four minutes

Which version sounds best depends on the situation:

• llega emphasizes arrival
• pasa emphasizes frequency/service interval
• hay emphasizes availability

A careful Spain pronunciation would be roughly:

el ME-tro YE-ga al an-DÉN KA-da KWA-tro mi-NU-tos

A few helpful notes:

• ll in much of Spain is pronounced like y in modern speech
• g in llega is a hard g sound here because it comes before a
• the stress falls on:
  • MEtro
  • YEga
  • anDÉN
  • KWAtro
  • miNUtos

Normally, no.

In standard Spanish, you need the article here: El metro.

Leaving out the article would sound incomplete or unnatural unless Metro were part of a headline, a label, or a special context. In an ordinary sentence, El metro llega al andén cada cuatro minutos is the correct form.