Nous étions sur le point de traverser quand une voiture a tourné trop vite au rond-point.

Because French is contrasting an ongoing background situation with a specific event that happened.

• Nous étions sur le point de traverser uses the imparfait (étions) to describe what was in progress or about to happen.
• une voiture a tourné uses the passé composé to describe the sudden event that interrupted that situation.

This is a very common pattern in French:

• imparfait = background, ongoing situation, setting
• passé composé = main event, completed action

So the sentence is structured like:

• We were just about to cross → background/in-progress idea
• when a car turned too fast → sudden event

If you said Nous avons été sur le point de traverser, it would sound much less natural here.

Sur le point de + infinitive means just about to, on the verge of, or about to do something.

So:

• sur le point de traverser = about to cross

It is a fixed expression. You do not translate it word for word in normal English, even though literally it is something like on the point of crossing.

Other examples:

• Il est sur le point de partir. = He is about to leave.
• J’étais sur le point d’appeler. = I was just about to call.

Notice that after de, you use the infinitive.

Because the expression is fixed as être sur le point de + infinitive.

So you say:

• être sur le point de partir
• être sur le point de traverser
• être sur le point de tomber

Not à.

This is something learners usually just need to memorize as part of the whole expression.

In French, traverser often means to cross and can sometimes appear without stating the object explicitly if the context makes it obvious.

So here, traverser likely means something like:

• cross the street
• cross the road
• cross over

French does this quite naturally when the thing being crossed is understood from the situation.

You could also say:

• traverser la rue = cross the street
• traverser la route = cross the road

But leaving it unstated is perfectly normal if everyone knows what is meant.

Quand means when, and here it introduces the event that happened at that moment.

Structure:

• Nous étions sur le point de traverser
• quand une voiture a tourné trop vite

This means something like We were just about to cross when a car turned too fast...

You could also sometimes see lorsque, which also means when, but quand is very common and natural in everyday French.

In this sentence, quand works especially well because it introduces the interrupting event.

Because a tourné presents the car’s turn as a single completed event.

Compare:

• une voiture a tourné = a car turned
• une voiture tournait = a car was turning / used to turn / was in the process of turning

In this sentence, the turning is the specific event that happened at that key moment, so passé composé is the natural choice.

This fits the common pattern:

• imparfait for what was going on: Nous étions...
• passé composé for what happened: une voiture a tourné...

This is an important vocabulary point.

• très vite = very fast
• trop vite = too fast

So trop implies excess or more than is acceptable/safe/normal.

In this sentence, une voiture a tourné trop vite suggests the car was going faster than it should have been, probably dangerously.

Examples:

• Il parle très vite. = He speaks very fast.
• Il parle trop vite. = He speaks too fast.

Because au is the contraction of à + le.

• à le rond-point becomes au rond-point

So:

• au rond-point = at the roundabout

This contraction is automatic in French:

• à + le = au
• à + les = aux

Examples:

• au parc
• au coin de la rue
• aux feux

Usually, au rond-point is the most natural choice here.

• au rond-point means at the roundabout, referring to the location in general.
• dans le rond-point would sound more like inside the roundabout, which is less natural in many contexts unless you really mean physically within it.

So if you are describing where the car turned, au rond-point is the normal expression.

Because tourné is part of the passé composé formed with avoir:

• une voiture a tourné

With avoir, the past participle usually does not agree with the subject.

So even though voiture is feminine, you still say:

• une voiture a tourné
• not une voiture a tournée

Agreement with a past participle is a different issue and usually happens:

• with être verbs, or
• with avoir only in certain cases when a preceding direct object is involved

But not here.

In everyday spoken French, many speakers would often use on instead of nous:

• On était sur le point de traverser quand une voiture a tourné trop vite au rond-point.

That sounds very natural in conversation.

However:

• nous étions is completely correct
• it can sound a bit more formal, careful, or written
• it is also very common in standard written French

So both are possible, but on était is often more conversational.

Étions is pronounced roughly like ay-tee-on with the final s silent.

A few useful points:

• é sounds like ay
• ti here sounds like tee
• ons sounds like a nasal vowel, roughly on without a strong final n
• the s is silent

So:

• nous étions ≈ noo zay-tee-on

Also note the liaison:

• nous étions is pronounced with a z sound linking the words

Yes, very much so.

It shows one of the most important storytelling patterns in French:

1. Set the scene / background with the imparfait
   • Nous étions sur le point de traverser
2. Introduce the event with the passé composé
   • quand une voiture a tourné trop vite au rond-point

This contrast is extremely common in French narratives, descriptions, and personal anecdotes.

For example:

• Je dormais quand le téléphone a sonné.
• Nous marchions quand il a commencé à pleuvoir.
• Elle lisait quand quelqu’un a frappé à la porte.

So this sentence is a very useful model to learn from.