Prefiero esa ruta porque hay menos tráfico.

Because preferir is a stem-changing verb. In the present tense, the e in the stem changes to ie in most forms:

• yo prefiero
• tú prefieres
• él/ella/usted prefiere
• nosotros/nosotras preferimos
• vosotros/vosotras preferís
• ellos/ellas/ustedes prefieren

So prefiero is the correct I prefer form.

Spanish often leaves out subject pronouns when they are not needed, because the verb ending already shows who is doing the action.
Here, prefiero clearly means I prefer, so yo is optional.

• Prefiero esa ruta = I prefer that route
• Yo prefiero esa ruta = also correct, but more emphatic

You might include yo if you want contrast, for example: Yo prefiero esa ruta, pero él no.

Spanish distinguishes demonstratives by distance or perspective:

• esta = this (near the speaker)
• esa = that (not near the speaker, or already mentioned)
• aquella = that over there / that one farther away

So esa ruta means that route. It suggests the speaker is referring to a particular route that is not being treated as this one right here.

Here, porque means because. It introduces the reason:

• Prefiero esa ruta porque hay menos tráfico.
• I prefer that route because there is less traffic.

A very common learner point is the difference between these forms:

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

In this sentence, porque is the standard word for because.

Hay means there is or there are. It comes from the verb haber and is used to talk about existence.

So:

• hay menos tráfico = there is less traffic

Spanish uses hay when saying that something exists or is present somewhere.
You would not use está here, because estar describes location or state, not existence in this way.

Compare:

• Hay tráfico. = There is traffic.
• El tráfico está mal hoy. = The traffic is bad today.

Because menos can directly modify a noun:

• menos tráfico = less traffic
• menos ruido = less noise
• menos gente = fewer people / less crowding

You do not need de before the noun in this structure.

You often see menos de only before numbers or quantities:

• menos de diez minutos = less than ten minutes
• menos de un euro = less than one euro

In Spanish, mass nouns like tráfico often appear without an article when speaking in a general sense.

• hay tráfico = there is traffic
• hay menos tráfico = there is less traffic

If you say el tráfico, you are usually talking about traffic in general as a concept or the traffic in a specific context:

• El tráfico en Madrid es terrible. = Traffic in Madrid is terrible.

In this sentence, menos tráfico is the natural general expression.

It is singular. Tráfico is usually treated as an uncountable noun, like traffic in English.

So you say:

• hay menos tráfico
• not hay menos tráficos

Even though traffic involves many cars, the noun itself is normally singular.

The accent mark shows the stress: trá-fi-co. The stress falls on the first syllable.

Without the accent, normal spelling rules would suggest a different stress pattern. The written accent makes the pronunciation clear and correct.

It is a esdrújula word in Spanish, and all esdrújulas take an accent mark.

Yes, a little, but the original order is the most natural.

Standard:

• Prefiero esa ruta porque hay menos tráfico.

You could also say:

• Porque hay menos tráfico, prefiero esa ruta.

That version is grammatical, but it sounds more marked or more like you are emphasising the reason first.

In everyday speech, the original sentence is the most straightforward choice.

Sometimes, yes, but they are not exactly the same.

• ruta = route / an itinerary or way to get somewhere
• camino = path, way, sometimes road
• carretera = road / highway

In this sentence, ruta is a good choice because the idea is I prefer that route—that particular way of going somewhere. If you said carretera, you would be talking more about the physical road itself rather than the route as a choice.

In standard Peninsular Spanish, a rough pronunciation guide is:

• Prefiero → preh-FYE-roh
• esa → EH-sa
• ruta → ROO-ta
• porque → POR-keh
• hay → eye
• menos → MEH-nos
• tráfico → TRA-fi-ko

A few useful points for Spain:

• r in ruta is tapped, not like an English r
• j does not appear here, so that part is straightforward
• the c in tráfico is a normal k sound because it is before o
• hay is just one syllable

A natural rhythm would be:

pre-FYE-ro EH-sa ROO-ta POR-ke ay MEH-nos TRA-fi-ko