La piétonne traverse la rue quand le feu est vert.

Piéton / piétonne means pedestrian, a person who is walking (not in a vehicle).

• piéton = masculine form (a male pedestrian, or a pedestrian of unspecified gender)
• piétonne = feminine form (a specifically female pedestrian)

In the sentence, the subject is grammatically feminine, so you get la piétonne rather than le piéton.

La is the definite article (“the”), while une is the indefinite article (“a”).

• La piétonne traverse la rue… can mean:
  • a specific pedestrian already known from context (the one we’re talking about), or
  • a general rule, like “The pedestrian crosses the street when the light is green.”

French often uses the definite article for general statements about a type of person or thing (e.g. Le chat aime le lait = “Cats like milk”).

French normally uses the simple present for both English “crosses” and “is crossing”.

So La piétonne traverse la rue can be understood as:

• “The pedestrian crosses the street”
• or “The pedestrian is crossing the street”

There is a way to emphasize an ongoing action:
La piétonne est en train de traverser la rue.
But in everyday French, the simple present traverse is usually enough.

Traverser takes a direct object, with no preposition:

• traverser la rue = to cross the street
• traverser le pont = to cross the bridge
• traverser la rivière = to cross the river

You do not say traverser dans la rue to mean “cross the street”; that would be incorrect in standard French.

French has several common words for “road/street”:

• la rue = a street in a town or city, where people live, walk, shop, etc.
• la route = a road for vehicles, often outside towns (main road, country road, highway)
• le chemin = a path, track, or small road

Since a piétonne is crossing what we imagine as a city street, la rue is the natural choice.

Yes, feu most commonly means “fire”, but it also means “traffic light” (signal at a junction).

In traffic contexts:

• le feu = the traffic light
• un feu rouge = a red light
• au feu rouge = at the red light

So quand le feu est vert means “when the (traffic) light is green,” not “when the fire is green.”

Adjectives in French agree with the gender and number of the noun they describe.

• feu is masculine singular, so the adjective must be masculine singular: vert.
• If the noun were feminine singular, you’d use verte:
  
  • la lumière est verte = the light is green

So:

• le feu vert (masc.)
• la lumière verte (fem.)

Quand means “when” and is the most common everyday choice.

Lorsque also means “when”, but it sounds a bit more formal or literary in many contexts. In this sentence you can use either:

• La piétonne traverse la rue quand le feu est vert.
• La piétonne traverse la rue lorsque le feu est vert.

The meaning is the same; quand is just more neutral and frequent in speech.

Here we have a general rule in the present, so both clauses use the present:

• La piétonne traverse la rue quand le feu est vert.
  = She crosses (in general) when the light is green (in general).

If we talk about a future action, French usually uses the future in both parts:

• La piétonne traversera la rue quand le feu sera vert.
  = She will cross the street when the light is green.

Note the contrast with English, which keeps the present after “when” (when the light is green) but uses the future in the main clause.

Yes. Both orders are correct:

• La piétonne traverse la rue quand le feu est vert.
• Quand le feu est vert, la piétonne traverse la rue.

When you put quand… at the beginning, you add a comma after the clause. The meaning is the same; starting with Quand le feu est vert just slightly emphasizes the time/condition.

You can make both the subject and the verb plural:

• Les piétons traversent la rue quand le feu est vert.
  = Pedestrians cross the street when the light is green.

Here:

• les piétons = pedestrians (masculine plural, but can include women)
• traversent = 3rd person plural of traverser

You could also say Les piétonnes if you specifically mean only female pedestrians.

Generally, no. Traverser la rue specifically means to cross from one side to the other.

Passer is more like:

• passer devant la maison = to go past / walk past the house
• passer la maison = to go beyond the house

So for “cross the street,” the natural verb is traverser la rue, not passer la rue.