Me molesta que el peaje de esa autopista sea tan caro en verano.

Because molestar here works like to bother / to annoy.

• Me molesta... = It bothers me...
• The thing that causes the annoyance is the subject of the verb.
• Me is an indirect object pronoun meaning to me.

So in this sentence, the thing that bothers you is:

• que el peaje de esa autopista sea tan caro en verano

Literally, the structure is closer to:

• It bothers me that the toll on that motorway is so expensive in summer.

By contrast, yo molesto means I bother / I annoy, which is a completely different idea.

Because after me molesta que..., Spanish normally uses the subjunctive.

The sentence expresses a reaction or feeling about a situation:

• Me molesta que... = It bothers me that...

When one clause expresses emotion, judgment, influence, doubt, etc., and the next clause is introduced by que, Spanish usually uses the subjunctive.

So:

• Me molesta que el peaje... sea tan caro ✅

not:

• Me molesta que el peaje... es tan caro ❌

Here, sea is the present subjunctive of ser.

The trigger is the pattern:

• emotion/reaction + que + subjunctive

In this case:

• Me molesta = an emotional reaction
• que = introduces the subordinate clause
• sea = subjunctive

Other similar examples:

• Me alegra que vengas. = I’m glad that you’re coming.
• Me sorprende que tenga tanto dinero. = It surprises me that he has so much money.
• Me preocupa que no estudien. = It worries me that they aren’t studying.

So the key idea is not just the word que, but the whole structure expressing a personal reaction.

Because the grammatical subject is singular.

The subject of molesta is the whole clause:

• que el peaje de esa autopista sea tan caro en verano

Spanish treats that entire que clause as a singular idea, so the verb is singular:

• Me molesta que... ✅

If the subject were plural, you would use molestan. For example:

• Me molestan los peajes tan caros. = Expensive tolls bother me.

But with a full subordinate clause, singular is normal:

• Me molesta que llegues tarde.
• Me molesta que hagan ruido.

They are related, but not the same.

• Me molesta que... focuses on what causes annoyance.

  • Me molesta que el peaje... sea tan caro.
  • It bothers me that the toll is so expensive.

• Estoy molesto/a describes your state or feeling.

  • Estoy molesto por el precio del peaje.
  • I’m annoyed about the toll price.

So:

• me molesta = something bothers me
• estoy molesto/a = I am annoyed

Both are natural, but the sentence you have is built around the cause of the annoyance.

This is the normal Spanish way to express possession or association.

• el peaje de esa autopista = the toll of / for that motorway

Spanish often uses de where English might use:

• ’s
• a noun-noun combination
• for / on

So English might say:

• that motorway’s toll
• the toll on that motorway

But Spanish naturally prefers:

• el peaje de esa autopista

This is very common:

• la puerta de la casa = the door of the house / the house door
• el precio del billete = the price of the ticket

In this sentence, peaje means the toll — the money you pay to use a road.

Depending on context, peaje can refer to:

• the toll charge itself
• the toll system
• sometimes, less precisely, the toll booth area

Here, because it says sea tan caro, it clearly refers to the price/cost of the toll.

In Spain, this is a very common word because some roads require payment.

These demonstratives show distance or perspective:

• esta = this
• esa = that
• aquella = that one over there / that more distant one

So:

• esa autopista = that motorway
  • not the one right here with me
  • not especially distant either
  • just one identified as that one

In everyday modern Spanish, esa is extremely common for that.

Using aquella would usually make the motorway sound more distant, less immediate, or more contrastive.

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

• muy caro = very expensive
• tan caro = so expensive

In this sentence, tan often sounds more natural because it emphasizes the speaker’s reaction:

• Me molesta que... sea tan caro = It bothers me that it’s so expensive

This fits well with emotional verbs like:

• me molesta
• me sorprende
• me fastidia
• me preocupa

Compare:

• Es muy caro. = It’s very expensive.
• Me molesta que sea tan caro. = It bothers me that it’s so expensive.

Because in Spanish, seasons are often used without the article after en.

So all of these are common:

• en verano = in summer
• en invierno = in winter
• en primavera = in spring
• en otoño = in autumn

You may also hear en el verano, and it can be correct, but en verano is very natural and common, especially for general statements.

A rough distinction:

• en verano = in summer, generally
• en el verano = in the summer, sometimes more specific depending on context

Here, en verano sounds perfectly natural because it means during summer in general.

Yes, to some extent.

The original sentence is fully natural:

• Me molesta que el peaje de esa autopista sea tan caro en verano.

You could also say:

• Me molesta mucho que el peaje de esa autopista sea tan caro en verano.
• En verano me molesta que el peaje de esa autopista sea tan caro.

These are still natural, but the emphasis changes slightly.

What you generally should keep is the core structure:

• Me molesta que + subjunctive

That structure is what makes the sentence grammatically work.

Yes — in Spain, autopista and autovía are related but not always identical.

Very roughly:

• autopista often suggests a high-capacity motorway, and many are or were toll roads
• autovía is also a major highway/dual carriageway, often without tolls

This is not a perfect one-to-one rule in every context, but for learners of Spanish from Spain, it is useful to know that autopista can strongly suggest the kind of road where peaje is relevant.

So el peaje de esa autopista sounds very natural in Peninsular Spanish.