Final answer:
Veins are the vessels that commonly contain valves to ensure unidirectional blood flow back to the heart, compensating for the lower blood pressure compared to arteries.
Step-by-step explanation:
The type of blood vessel that most commonly contains valves is veins.
Veins are responsible for carrying blood toward the heart. Due to the lower pressure in veins compared to arteries, veins are equipped with valves to prevent backflow and ensure unidirectional blood flow.
Arteries, which carry blood away from the heart, have thicker walls to withstand high pressure but typically do not contain valves except for the pulmonary artery and aorta, which have semilunar valves at their origination point in the heart. In contrast, capillaries, being the smallest blood vessels and sites of exchange, do not have valves.