Final answer:
The phenomenon where consumers can buy more gasoline due to its lower price is described by the income effect, which increases consumers' effective buying power, allowing them to afford more with the same amount of money.
Step-by-step explanation:
As a result of a decrease in the price of gasoline, consumers can afford to buy more gasoline for more driving trips. This is an illustration of the income effect. The income effect describes how a change in the price of a good alters the effective buying power of one's income. When the price of gasoline decreases, consumers feel as though they have more money to spend - their purchasing power has increased - and they can now afford more gasoline. This effect is different from the substitution effect, which encourages consumers to use less of a product when it becomes relatively more expensive and switch to a cheaper alternative. However, in the case of gasoline getting cheaper, consumers will purchase more gasoline rather than finding another substitute.
In summary, a decrease in gasoline prices means that people have a higher purchasing power and can therefore buy more goods, as is observed with the consumption of more gasoline. This shift in consumer behavior when faced with a decrease in prices is directly attributable to the income effect.