The driver is the wild symbol, he can land on reels two, three and four, and he will substitute for all of the other symbols, except for the scatter and bonus symbols, to help and form winning combinations.
The scatter symbol is the cowgirl and the bonus symbol is a chequered flag.
The first thing worth mentioning about this slot is that while there may only be nine paylines, they will payout in both directions. This means that you can form winning combinations starting from the leftmost reel or the rightmost reel. Essentially, it doubles the number of paylines without increasing the amount you need to bet.
The Truck Racing Bonus begins when you land the chequered flag bonus symbol on reels one and five simultaneously. You first need to choose one of the three trucks to reveal how many free spins you have won, up to 25. The trucks will then race to reveal a payout multiplier of up to 5x. The free spins then begin. If, during the free spins, you land the bonus symbol on reels one and five simultaneously then you will be awarded twenty more free spins. This way it is possible to win free spins indefinitely.
Highway Kings Pro offers a top payout of 10,000x for landing five of the red truck symbols along a payline. The petrol pumps can payout up to 5,000x, the green and yellow trucks can both payout up to 1,000x, the dice and the cap can both payout up to 300x, the sparkplugs can both payout up to 200x, and the steering wheel and wheel can both payout up to 50x. The scatter symbol offers payouts of up to 100x the total bet for a spin when five land on the reels.