Pasamos por donde está el cruce ciclista.

Because for nosotros, the present and preterite forms of many -ar verbs look identical.

• pasamos = we pass / we go by (present)
• pasamos = we passed / we went by (preterite)

So this sentence is ambiguous by itself. Context tells you which one it means.

Examples:

• Cada día pasamos por donde está el cruce ciclista. = Every day we go by where the bike crossing is.
• Ayer pasamos por donde está el cruce ciclista. = Yesterday we went by where the bike crossing is.

Spanish often drops subject pronouns because the verb ending already tells you who the subject is.

• pasamos already tells you the subject is we
• So Nosotros pasamos... is possible, but usually unnecessary

You would include nosotros only for emphasis, contrast, or clarity.

For example:

• Nosotros pasamos por donde está el cruce ciclista, pero ellos no.

Here, por donde means something like:

• by where
• through where
• past the place where

The preposition por adds the idea of movement along/through/past a place.

So:

• Pasamos por donde está el cruce ciclista = We go/went by the place where the bike crossing is

If you used only donde, you would lose some of that idea of movement through/by a place.

Because this is not a question and not an exclamation. It is a relative adverb, so it has no accent: donde.

Compare:

• ¿Dónde está el cruce ciclista? = question → dónde
• Pasamos por donde está el cruce ciclista. = statement/relative clause → donde

A useful rule:

• dónde = in direct or indirect questions
• donde = in statements like this one

Because the sentence is talking about location.

In Spanish, estar is used for where something is located:

• El cruce ciclista está aquí.
• ¿Dónde está el cruce ciclista?

Using es would sound wrong here, because ser is not normally used for physical location of things or places.

So donde está el cruce ciclista means where the bike crossing is located.

Cruce ciclista means a bicycle crossing or cyclist crossing.

• cruce = crossing
• ciclista = cyclist / cycling-related

Here ciclista describes the type of crossing: one intended for bicycles or cyclists.

Depending on the country or context, you might also see other expressions, such as:

• paso ciclista
• cruce para ciclistas
• cruce de bicicletas

But in this sentence, cruce ciclista is simply the label for that kind of crossing.

It is a clause that identifies a place.

You can think of por donde está el cruce ciclista as a shortened way of saying:

• por el lugar donde está el cruce ciclista

So grammatically:

• por = preposition
• donde está el cruce ciclista = clause meaning where the bike crossing is

Together they mean through/by the place where the bike crossing is.

Because donde está el cruce ciclista is the most natural word order in Spanish.

Spanish often places the verb before the subject in clauses like this, especially when identifying location:

• donde está el cruce ciclista = natural
• donde el cruce ciclista está = possible only in very marked or poetic language, but not normal here

So this word order is just the standard, idiomatic way to say it.

It is much more natural to keep por with pasar here.

Pasar por is a very common combination meaning:

• to pass by
• to go through
• to go via

So:

• Pasamos por donde está el cruce ciclista = natural

Without por, the sentence sounds less standard and may feel incomplete or less precise, because por is what gives the idea of moving by/through that place.

No. Pasar por often is physical, as in this sentence, but it can also have other meanings.

Some common uses:

• Pasar por la plaza = go through/by the plaza
• Pasar por alguien = pick someone up
• Pasar por una situación difícil = go through a difficult situation
• Pasar por médico = pass oneself off as a doctor

In your sentence, though, it is the straightforward physical meaning: to pass by / go through a place.