At this intersection, where the right-of-way is not marked by signs, which vehicle will go last?

Correct answer: The motorcycle.

With no signs, everyone yields to the vehicle on their right. The blue vehicle has no one approaching from its right and goes first. The red vehicle, which had the blue vehicle on its right, goes second. The motorcycle has the red vehicle on its right and goes last.

Real Decreto 1428/2003, de 21 de noviembre, por el que se aprueba el Reglamento General de Circulación