On a road with two lanes in the same direction, when is the driver of a passenger car required to change lanes completely and drive in the lane on their left?

Correct answer: When passing human-powered cycles or mopeds.

With two lanes in your direction, you must move completely into the left lane to pass a human-powered cycle (ciclo) or a moped; moving only partly into it is not enough. The rule is not limited to bicycles and also applies to pedestrians, animals, carts, and personal mobility vehicles. What matters is who or what you are passing, not whether they are on the shoulder.

Real Decreto 1428/2003, de 21 de noviembre, por el que se aprueba el Reglamento General de Circulación · Real Decreto Legislativo 6/2015, de 30 de octubre, por el que se aprueba el texto refundido de la Ley sobre Tráfico, Circulación de Vehículos a Motor y Seguridad Vial