The Summer Road Trip is a special set that was made available during the 2020 Summer Sale.
There are 10 cards in the series, and you could earn one card per day by going through your Discovery Queue. You could also earn a card by crafting a badge from any other card set - doing so would give you a random card from the set in addition to the normal badge crafting rewards. Additionally, every 10$ spent in the store would grant you a random card.
All Summer Road Trip cards expired on 9 August 2020, at 11AM PST.