The thrust of these policies relies on capping vehicle growth. Buyers must have successfully bid for a certificate of entitlement (COE) before they can buy a new car. As the COE is valid only for ten years, this requirement lowers the average age of cars on the road and also C02 emission as older cars pollute more and are less energy efficient. The COE may be extended for another five years on payment of an additional fee but the vehicle must pass annual road worthiness tests.