El taxista nos dijo que había mucho tráfico en la autopista.

Nos means to us.

In El taxista nos dijo..., it is an indirect object pronoun: the taxi driver told us something.

Spanish object pronouns usually go before a conjugated verb:

• Nos dijo = he told us
• Me dijo = he told me
• Les dijo = he told them / you all

So nos dijo is the normal word order.

Dijo is the preterite, and it presents the act of telling as a completed event.

So El taxista nos dijo... means that at some point, the taxi driver told us this.

If you used decía, it would sound more like:

• he was saying
• he used to say
• or it would describe the action as background information rather than a single completed act

In this sentence, Spanish normally uses dijo because the telling happened once and is treated as a finished action.

This is a very common question because it involves reported speech.

If the taxi driver originally said something like:

• Hay mucho tráfico en la autopista

and you later report it in the past, Spanish often shifts the tense back:

• El taxista nos dijo que había mucho tráfico en la autopista

So:

• hay = there is
• había = there was / there used to be / there was at that time

Here, había matches the past reporting verb dijo and describes the traffic situation at that moment in the past.

Because Spanish uses haber for there is / there are / there was / there were.

So:

• había mucho tráfico = there was a lot of traffic

You do not use estar for that kind of existence sentence.

Compare:

• Había mucho tráfico en la autopista = There was a lot of traffic on the motorway
• El coche estaba en la autopista = The car was on the motorway

So haber is used to say that something existed or was present, while estar is used to say where a specific thing was.

Because tráfico is normally an uncountable noun in this meaning, just like traffic in English.

So Spanish says:

• mucho tráfico = a lot of traffic

Not:

• muchos tráficos

Mucho stays singular because tráfico is being treated as a mass noun, not as separate countable items.

Que introduces the clause that contains what was said.

So:

• nos dijo que... = he told us that...

This is standard after verbs like:

• decir = to say / tell
• pensar = to think
• creer = to believe
• saber = to know

In English, that is often optional:

• He told us that there was a lot of traffic.
• He told us there was a lot of traffic.

In Spanish, que is normally required here.

El means the, so El taxista means the taxi driver.

Spanish uses the definite article here because it is referring to a specific taxi driver, not taxi drivers in general.

So:

• El taxista nos dijo... = The taxi driver told us...

This does not mean Spanish always uses the article just because it is a profession. It is simply identifying a particular person.

Because en is used for location here.

• en la autopista = on the motorway / on the highway

The traffic is located there, so en is the natural preposition.

By contrast, a usually suggests movement toward a place:

• Vamos a la autopista = We’re going to the motorway

So in this sentence, en is correct because it describes where the traffic was.

They are similar, but not always exactly the same.

In Spain, both autopista and autovía can refer to major high-speed roads, but there can be technical differences:

• autopista often suggests a fully controlled-access motorway, sometimes with tolls
• autovía is also a major dual carriageway, but historically developed differently and is often toll-free

In everyday learning, both are often translated as motorway or highway, but in Spain the distinction can matter.

Yes, Spanish word order is more flexible than English.

You can say:

• El taxista nos dijo que había mucho tráfico en la autopista
• Nos dijo el taxista que había mucho tráfico en la autopista

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

The version starting with El taxista is the most neutral and straightforward.
Starting with Nos dijo can sound a bit more marked, depending on context.

Because this sentence is reporting information that the speaker presents as a statement, so Spanish uses the indicative:

• dijo que había...

After decir que, the indicative is normal when you are reporting what someone said as factual content.

You would not use the subjunctive here unless the structure changed a lot or the sentence expressed doubt, command, emotion, or another trigger.

So:

• dijo que había mucho tráfico = normal reported statement
• not dijo que hubiera mucho tráfico in this context

Yes, that is possible, especially in Spain.

In Spain Spanish, the present perfect is often used for recent past actions connected to the present:

• El taxista nos ha dicho que había mucho tráfico...

That can sound natural if the taxi driver told you very recently, for example today.

But dijo is also completely correct. It simply presents the event as a finished past action.

So both can be right, depending on the time frame and the speaker’s preference.