Hoy he hecho otro transbordo porque olvidé validar la tarjeta al salir.

In Spain Spanish, it is very common to use the present perfect for actions connected to today, this week, this year, etc.

So:

• Hoy he hecho otro transbordo = Today I’ve made another transfer
• Ayer hice otro transbordo = Yesterday I made another transfer

The idea is that today is still part of the speaker’s current time frame, so he hecho sounds very natural in Spain.

In much of Latin America, many speakers would more often say Hoy hice... instead.

Spanish does not always have to keep the same past tense throughout a sentence.

Here, the speaker says:

• Hoy he hecho otro transbordo → an action in the time period of today
• porque olvidé validar la tarjeta → the specific completed action that caused it

Using olvidé is perfectly natural. It presents the forgetting as a finished event.

You could also hear porque he olvidado validar la tarjeta, but olvidé sounds very normal and idiomatic here.

So the sentence mixes:

• present perfect for the broader event linked to today
• preterite for the specific completed cause

Transbordo means a transfer or change from one form of transport to another, especially in public transport.

For example:

• changing from one metro line to another
• getting off one bus and taking another
• switching trains during a journey

In this sentence, otro transbordo suggests the speaker had to make an additional transfer.

In transport contexts, transbordo is a very common word in Spain.

In Spanish, otro normally does not use the indefinite article un/una before it.

So you say:

• otro transbordo
• otra vez
• otro día

Not:

• un otro transbordo

This is just a normal rule of Spanish grammar.

Compare:

• un transbordo = a transfer
• otro transbordo = another transfer

Spanish often omits subject pronouns when the verb already shows who the subject is.

Here:

• he hecho clearly means I have done / I have made
• olvidé clearly means I forgot

So yo is unnecessary unless the speaker wants emphasis or contrast.

For example:

• Hoy he hecho otro transbordo... = neutral
• Yo he hecho otro transbordo... = more emphasis, like I did another transfer

This is very normal in Spanish.

In public transport in Spain, validar means to scan, tap, or validate your ticket or travel card at the machine.

So validar la tarjeta means something like:

• tap the card
• scan the card
• validate the card for the journey

This is a very common transport verb in Spain.

Even if validate sounds slightly formal in English, in Spanish validar is the standard word in this context.

Al + infinitive is a very common Spanish structure meaning:

• when ...
• upon ...
• on ...-ing

So:

• al salir = when leaving / upon leaving / on the way out

It is formed from:

• a + el = al
• plus an infinitive

Examples:

• Al llegar, te llamo. = When I arrive, I’ll call you.
• Al entrar, saludó a todos. = Upon entering, he greeted everyone.

In your sentence, al salir means the card had to be validated when exiting.

Because here it means because.

Spanish distinguishes these forms:

• porque = because
• por qué = why
• el porqué = the reason
• por que = a less common combination used in certain structures

So in this sentence:

• porque olvidé validar la tarjeta = because I forgot to validate the card

If it were a question, you would use por qué:

• ¿Por qué hiciste otro transbordo? = Why did you make another transfer?

The accent mark shows both pronunciation and meaning.

• olvidé = I forgot
• olvide could be interpreted as a different verb form, such as a subjunctive or formal command context

The accent tells you the stress falls on the last syllable:

• ol-vi-DÉ

It also helps distinguish the first-person preterite form from other forms.

This is common with many verbs:

• hablé
• compré
• llegué

Yes, it is normal and idiomatic.

Spanish often uses hacer with nouns to express actions, where English might prefer a single verb or a different phrase.

So:

• hacer un transbordo = to make a transfer
• hacer un cambio = to make a change

In transport contexts, you may also hear:

• hacer transbordo
• tener que hacer otro transbordo

All of these are natural.

Yes. In this context, la tarjeta most likely means a travel card or transport card, not a bank card.

In Spain, tarjeta can refer to many kinds of cards:

• tarjeta bancaria = bank card
• tarjeta de transporte = transport card
• tarjeta sanitaria = health card

Because the sentence talks about validar and al salir, the transport meaning is the natural one here.

Both are possible, but they are slightly different in feel.

• al salir = when leaving / upon exiting
• cuando salí = when I left

Al salir is more compact and general. It focuses on the moment of exiting as part of the process.

Cuando salí sounds a bit more like a narrated past event.

In this sentence, al salir is very natural because it refers to the required action at the exit point: validating the card when leaving.

Yes, in a couple of ways.

Two especially noticeable features are:

• Hoy he hecho...
  This use of the present perfect with hoy is very typical in Spain.

• validar la tarjeta
  This is very common transport vocabulary in Spain.

A speaker from Latin America might understand the sentence perfectly but might be more likely to say something like:

• Hoy hice otro transbordo... depending on the country.

So the sentence sounds very naturally Peninsular Spanish, especially in an urban public-transport context.