No conviene acelerar en esa curva, y tampoco se puede adelantar cuando hay niebla.

Convenir often means to be advisable / to be suitable / to be a good idea.

In this sentence, no conviene acelerar is an impersonal way of saying:

• It’s not advisable to speed up
• It’s not a good idea to accelerate

This is very common in Spanish when giving general advice, especially in formal or neutral language.

A few comparisons:

• No conviene correr aquí. = It’s not advisable to run here.
• No conviene discutir ahora. = It’s not a good idea to argue now.

So no conviene is not about strict prohibition; it sounds more like sensible advice.

Because after conviene, Spanish often uses an infinitive to talk about an action in general.

So:

• No conviene acelerar = It’s not advisable to accelerate

This works like English to + verb after expressions such as it’s good to..., it’s better to..., it’s advisable to...

More examples:

• Conviene esperar. = It’s advisable to wait.
• No conviene salir tan tarde. = It’s not advisable to go out so late.

You could also make the subject explicit:

• No conviene que aceleren. = It’s not advisable that they accelerate.

But with general instructions or advice, the infinitive is very natural.

Spanish demonstratives show distance, and in Spain the three-way distinction is still very standard:

• esta = this, near the speaker
• esa = that, near the listener or at a medium distance
• aquella = that over there, farther away

So esa curva means that curve.

In many contexts, esa simply points to a specific curve that both speaker and listener know about. It does not always have to imply literal physical distance in a strict way.

Also, curva is feminine singular, so the demonstrative must match:

• esta curva
• esa curva
• aquella curva

The preposition en is commonly used for location and for something happening on / in / at a stretch of road, bend, area, or place.

So:

• en esa curva = on / at that bend

This is idiomatic Spanish for talking about what happens at a certain point on the road.

Examples:

• Hay un accidente en esa curva. = There is an accident at that bend.
• Tienes que frenar en la curva. = You have to brake on the bend.

English and Spanish do not always use the same preposition, so en is just the natural choice here.

Tampoco means not either, nor, or neither depending on context.

Here it links a second negative idea to the first one:

• No conviene acelerar..., y tampoco se puede adelantar...
• It’s not advisable to accelerate..., and you can’t overtake either...

It adds the sense of also not.

Compare:

• No puedo ir y tampoco puedo llamar. = I can’t go, and I can’t call either.
• No me gusta el café, y tampoco el té. = I don’t like coffee, nor tea either.

Since the first clause is negative, tampoco fits naturally.

Se puede + infinitive is a very common impersonal structure in Spanish. It means something like:

• one can
• you can in a general sense
• it is possible / allowed to

So no se puede adelantar means:

• You can’t overtake
• It is not possible / allowed to overtake
• One cannot overtake

It is not talking to one specific person; it expresses a general rule.

Compare:

• Aquí no se puede fumar. = You can’t smoke here.
• Se puede aparcar en esta calle. = You can park in this street.

This is especially common for rules, signs, and general instructions.

It can suggest either, depending on context.

In road language, no se puede adelantar often means something like:

• you must not overtake here
• overtaking is not allowed / not safe / not possible

Because the sentence mentions cuando hay niebla, the idea is probably a mix of safety and practical impossibility: when there is fog, overtaking is not something you should or can do safely.

If Spanish wants to sound more clearly like an obligation or prohibition, it might say:

• No se debe adelantar. = You must not overtake.
• Está prohibido adelantar. = Overtaking is forbidden.

So no se puede is slightly broader and softer than a direct prohibition, though in many real contexts it still functions like one.

Adelantar has several related meanings, and one very common one in driving is to overtake / to pass another vehicle.

So here:

• adelantar = to overtake

Other meanings of adelantar include:

• to move something forward
• to bring something forward in time
• to get ahead
• to advance

Examples:

• El coche adelantó al camión. = The car overtook the lorry/truck.
• Han adelantado la reunión. = They moved the meeting forward.
• Adelántate un poco. = Move a bit further forward.

In traffic contexts, adelantar very often means to overtake.

Because hay is used to say there is / there are, including when talking about the presence of weather conditions or things in general.

So:

• hay niebla = there is fog

This is the normal way to say that fog is present.

Examples:

• Hay niebla. = There is fog.
• Hay mucho tráfico. = There is a lot of traffic.
• Hay hielo en la carretera. = There is ice on the road.

Using estar would not work the same way here. Spanish normally says hay niebla, not está niebla.

Spanish often leaves out the article when speaking about something in a general, indefinite way, especially with uncountable nouns or weather-related conditions.

So:

• hay niebla = there is fog

not usually:

• hay la niebla

Similarly:

• Hay humo. = There is smoke.
• Hay nieve. = There is snow.
• Hay polvo. = There is dust.

If you add an article, it usually becomes more specific:

• La niebla de esta mañana era muy densa. = The fog this morning was very thick.

But in cuando hay niebla, it is just talking about fog in general.

Here it is best understood as an impersonal se construction.

• No se puede adelantar = You/one cannot overtake

There is no real subject here. It is a general statement.

This is different from a true passive-like sentence such as:

• Se venden coches. = Cars are sold.

In se venden coches, coches is the grammatical subject, and the verb agrees with it.

But in:

• Se puede adelantar

the verb stays in the singular because the structure is impersonal and is followed by an infinitive.

So for learners, the easiest way to understand it is:

• se puede + infinitive = one can / you can / it is possible to

Spanish often prefers concise, impersonal structures for general advice and rules.

This sentence gives two linked ideas:

1. No conviene acelerar en esa curva
2. tampoco se puede adelantar cuando hay niebla

The connector y tampoco works like and also not / and not either.

It sounds natural and efficient, especially in formal or instructional language. A more explicit version might be:

• No conviene acelerar en esa curva, y además no se puede adelantar cuando hay niebla.

That is possible, but tampoco is more elegant because the first clause is already negative.

It sounds like a mixture of all three, but each part has a slightly different force:

• No conviene acelerar... = advice / warning
  It suggests what is wise or sensible.
• No se puede adelantar... = rule / practical restriction / warning
  It suggests that overtaking is not something permitted or safely possible.

So the overall tone is very natural for road safety language: neutral, general, and cautionary rather than emotional.

If the speaker wanted to sound stronger, they might say:

• No aceleres en esa curva. = Don’t accelerate on that bend.
• No adelantes cuando hay niebla. = Don’t overtake when there is fog.

Those are direct commands. The original sentence sounds more like objective guidance.