Según el pronóstico, gastaremos más gasolina si hay embotellamiento en la autopista.

Según means according to. So Según el pronóstico = According to the forecast/prediction. It’s a common way to introduce the source of information. You can also see según with people: Según mi jefe... = According to my boss... (i.e., “my boss says…”).

Not only. Pronóstico often refers to a weather forecast, but it can also mean a prediction/forecast in general (traffic, sales, medical prognosis, etc.). In this sentence it could be weather-related or a general prediction—context decides.

Gastaremos is the simple future of gastar (to spend/use up), nosotros form: we will spend/use. Spanish often uses the simple future where English might use will or sometimes are going to, depending on certainty and style.

Yes. Vamos a gastar más gasolina is very natural in Latin America and is often used for near-future or planned/expected results.

• Gastaremos más gasolina sounds a bit more formal or “forecast-like.”
  Both mean essentially we’ll use more gas.

After si (meaning if), Spanish uses the indicative for real/possible conditions:

• si hay = if there is / if there’s (possible, realistic)

The subjunctive doesn’t follow si in this kind of “if” clause. Subjunctive appears in other structures (like aunque, cuando for future uncertainty, etc.), but not here.

Use si + imperfect subjunctive for hypothetical/unreal situations:

• Gastaríamos más gasolina si hubiera embotellamiento. = We would use more gas if there were a traffic jam.
  That’s the conditional (“would”) pattern: si + hubiera → gastaríamos.

Embotellamiento means traffic jam / gridlock. It’s widely used in Latin America. Other common options by region:

• trancón (very common in Colombia/Venezuela)
• atasco (more common in Spain, but understood)
• congestión (vehicular) (more formal)

• autopista: typically a major highway/freeway, often multi-lane, sometimes toll-based depending on the country.
• carretera: a more general road/highway, can be smaller.
• ruta: common in some countries (e.g., Argentina/Chile) for highway/route (like Route 5).
  So en la autopista emphasizes a big highway where traffic jams can happen.

In Spanish, with quantities like this, you usually say más + noun directly:

• más gasolina, más agua, más tiempo

Más de is used when a number follows:

• más de 10 litros de gasolina = more than 10 liters of gas

Gastar gasolina means to use up/consume gas (to burn fuel). If you mean to buy gas, you’d say something like:

• comprar gasolina (to buy gas)
• echar gasolina / poner gasolina (to get gas / to fill up; very common in Latin America)

el pronóstico uses el because it’s referring to a specific forecast (the one being discussed).
With hay, Spanish often omits articles because it’s introducing something as existence/occurrence:

• hay embotellamiento = there is traffic (a traffic jam)
  Adding an article can change the nuance: hay un embotellamiento sounds more like there is a (particular) traffic jam, more specific.

Yes, both are correct:

• Según el pronóstico, gastaremos más gasolina si hay embotellamiento en la autopista.
• Según el pronóstico, si hay embotellamiento en la autopista, gastaremos más gasolina.
  Spanish is flexible with clause order; commas help readability when the if-clause comes first.