Si el metro no funciona, hi anirem a peu.

Here hi means there or to that place. It is a locative pronoun that replaces a destination already understood from context.

For example:

• Anirem al centre a peu. = We’ll go to the center on foot.
• Hi anirem a peu. = We’ll go there on foot.

So in your sentence, hi stands for the place you were planning to go.

In Catalan, weak pronouns like hi normally go before a conjugated verb.

So:

• hi anirem
• not anirem hi

This is very normal Catalan word order.
If the verb were an infinitive, gerund, or imperative, the position could change, but with a normal conjugated future form like anirem, hi comes before it.

Because Catalan uses the present indicative after si in real or likely conditions, even when the result is in the future.

So the pattern is:

• Si + present, future

In this sentence:

• Si el metro no funciona = If the metro isn’t working / doesn’t run
• hi anirem a peu = we’ll go there on foot

This is similar to English, which also says If it rains, we’ll stay home, not If it will rain...

In standard Catalan, no. After si in this kind of condition, you normally use the present indicative, not the future.

So the correct form is:

• Si el metro no funciona, hi anirem a peu.

Not:

• Si el metro no funcionarà, hi anirem a peu.

This is an important pattern to remember:

• si + present
• main clause often in future, present, or imperative

Anirem is the 1st person plural future of anar = to go.

So:

• aniré = I will go
• aniràs = you will go
• anirà = he/she/it will go
• anirem = we will go
• anireu = you all will go
• aniran = they will go

So hi anirem means we will go there.

A peu means on foot or walking.

It is a fixed expression in Catalan:

• anar a peu = to go on foot
• venir a peu = to come on foot

Even though English says on foot, Catalan uses a peu, not en peu.

Examples:

• Vaig a la feina a peu. = I go to work on foot.
• Hi anirem a peu. = We’ll go there on foot.

Yes. Funcionar is very commonly used for machines, systems, services, and transport.

So el metro no funciona can mean things like:

• the metro isn’t working
• the metro isn’t running
• the metro service is not operating

It sounds natural in Catalan. English often prefers isn’t running or isn’t operating for public transport, but Catalan uses funcionar very naturally here.

Not if you want the sentence to keep the meaning go there without naming the place.

Compare:

• Si el metro no funciona, hi anirem a peu. = If the metro doesn’t work, we’ll go there on foot.
• Si el metro no funciona, anirem a peu. = If the metro doesn’t work, we’ll go on foot.

The second sentence is understandable, but it no longer explicitly includes there.
So hi is important if the destination is being replaced rather than stated directly.

Because metro is masculine in Catalan, so it takes el.

• el metro

This is worth learning as a noun/article pair. Grammatical gender in Catalan does not always match what an English speaker might expect, so it is best to memorize nouns with their article.

The comma is standard and natural when the si clause comes first:

• Si el metro no funciona, hi anirem a peu.

It helps separate the condition from the main clause. In short, it is the normal written punctuation here.

If the order were reversed, the comma would often disappear:

• Hi anirem a peu si el metro no funciona.

Both versions are correct; the first simply puts the condition first.