Si el metro va lleno, habrá que hacer otro transbordo o esperar en la marquesina del autobús.

Metro is a masculine noun, so it takes el: el metro.

In this sentence, el metro most naturally refers to the metro train/service being used, not just the whole subway system in the abstract, because va lleno describes how it is running at that moment: crowded/full.

Both can be possible, but va lleno is very natural for transport.

With vehicles, ir + adjective often describes the condition they are going in:

• El autobús va lleno = the bus is going along full / the bus is crowded
• El tren va vacío = the train is going along empty

So va lleno focuses on the metro as it is running.
Está lleno would simply describe its state: it is full.

In everyday transport Spanish, va lleno often sounds more idiomatic here.

Because this is a real or possible condition, not an unreal or hypothetical one.

• Si el metro va lleno, habrá que... = If the metro is full, we’ll have to...
• Si el metro estuviera lleno, habría que... = If the metro were full, we would have to...

After si, Spanish normally uses:

• present indicative for real/possible situations
• imperfect subjunctive for hypothetical ones

So si el metro va lleno is exactly what you would expect here.

Habrá que + infinitive means it will be necessary to..., one will have to..., or more naturally in English, we’ll have to...

So:

• habrá que hacer otro transbordo = we’ll have to make another transfer
• habrá que esperar = we’ll have to wait

It comes from the impersonal structure haber que + infinitive.

Because haber que is an impersonal structure.

Spanish often leaves the subject vague when the meaning is general:

• Hay que salir = one has to leave / we have to leave
• Habrá que esperar = one will have to wait / we’ll have to wait

So the sentence does not literally say we, but English often translates it that way because that is the most natural interpretation in context.

Both are possible, but they do not sound exactly the same.

• Habrá que = more impersonal, more neutral
• Tendremos que = more direct, clearly we will have to

Compare:

• Si el metro va lleno, habrá que esperar = If the metro is full, we’ll have to wait
• Si el metro va lleno, tendremos que esperar = If the metro is full, we will have to wait

The second sounds a bit more personal and explicit. The original sentence sounds more general and matter-of-fact.

Yes. Hacer transbordo is a standard transport expression meaning to make a transfer, to change, or to switch from one line/vehicle to another.

So hacer otro transbordo means:

• make another transfer
• change again
• switch to another line/route again

The noun transbordo is a transfer/change, and hacer transbordo is a very common collocation.

Otro means another or one more.

So otro transbordo suggests that:

• there has already been a transfer, or
• at least one transfer is already expected, and now an additional one may be necessary

It gives the idea of an extra change, not the first one.

In Spain, la marquesina usually means the covered structure at a bus stop: the bus shelter.

So esperar en la marquesina del autobús means waiting at the sheltered bus stop area, not just anywhere near the bus route.

This is very natural in Spain Spanish. In other Spanish-speaking countries, other terms may be more common depending on the region.

Because en la marquesina tells you where you are waiting.

• esperar en la marquesina = wait at/in the shelter

If you say what you are waiting for, esperar usually takes a direct object:

• esperar el autobús = wait for the bus

With people, Spanish often uses the personal a:

• esperar a Marta = wait for Marta

So here, en is not linked to esperar itself; it simply gives the location.

Yes, sometimes.

• cambiar de línea = to change lines
• hacer transbordo = to make a transfer

Cambiar de línea is more specific: it focuses on switching from one line to another.
Hacer transbordo is the more standard transport term and can be broader, including changing between different services or vehicles.

So in this sentence, hacer otro transbordo sounds very natural and slightly more idiomatic.

Because Spanish can avoid repetition when the meaning is clear.

The full idea is:

• habrá que hacer otro transbordo o habrá que esperar

But repeating habrá que is unnecessary, so Spanish leaves it out in the second part:

• habrá que hacer otro transbordo o esperar

This is completely normal and works the same way in English:

• We’ll have to make another transfer or wait

The second verb is understood as part of the same structure.