Learn Hardcore Portuguese (Brazil): Quando a curva é fechada, o motorista deve diminuir a velocidade. - When the curve is sharp, the driver must reduce the speed.

Breakdown of Quando a curva é fechada, o motorista deve diminuir a velocidade.

Why is it fechada and not fechado?

Because fechada agrees with curva, and curva is a feminine noun in Portuguese.

If the noun were masculine, the adjective would normally be masculine too.

This kind of agreement is very common in Portuguese:

So here, fechada matches curva.

Does fechada literally mean closed here?

Literally, yes, fechado / fechada often means closed. But in this sentence it has a different, very common extended meaning.

With roads and turns, curva fechada means a sharp or tight curve, not a physically closed one.

So this is a good example of how a familiar word can have a more specific meaning depending on context.

Why does the sentence use é fechada instead of está fechada?

Because ser is being used to describe a characteristic of the curve, not a temporary condition.

é fechada = it is a sharp/tight curve
está fechada would suggest something temporary, and with fechada it could even sound like the road or route is blocked/closed

In Portuguese, ser is generally used for inherent description or classification, while estar is used for states or temporary situations.