Learn Spanish (Spain): Los trenes no circulaban cuando la incidencia afectó a la línea. - The trains were not running when the incident affected the line.

This is a classic example of how two past tenses work together. We use the imperfect tense circulaban for the background action that was ongoing (the trains were not running). We use the preterite tense afectó for the specific event that happened at a clear point in time (the incident affected the line).

Why use circulaban instead of a word like corrían for trains running?

In English, we say trains or buses are running, but in Spanish, vehicles do not use the verb correr (to run). Instead, we use the verb circular, which means to move around, circulate, or travel along a route.

Does incidencia just mean any type of incident?

While it translates to incident, in Spain incidencia is heavily used to mean a glitch, breakdown, or service disruption. You will hear it constantly on public transport or with tech issues when something is not working normally.

Why is there an a before la línea? Is it the personal a?

It is not the personal a because a train line is not a person. Instead, the verb afectar (to affect) almost always requires the preposition a before the thing or person being affected. You can think of it as causing an effect to something.