In case of a contradiction between signs of the same type, which one will prevail?

Correct answer: The most restrictive one.

If two signs of the same type appear to contradict each other, obey the more restrictive one. In the image, the yield sign and the STOP sign are on the same pole, and both are posted signs. The STOP sign takes priority, so the driver comes to a complete stop before crossing and then yields. For different types of signs or signals, however, the order of priority applies.

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