I love the Mad Max films. Their action scenes are gritty, senseless, depraved and violent. Chaos rather than competence wins the day; the heroes are more lucky than skilled.
Adrenaline dice are a sub-system of vehicular combat that promote chaos and mayhem. Players roll the adrenaline dice at the beginning of each segment of combat (turn, round, whatever your system calls for.) Each instance of doubles on the adrenaline dice allows the player to call for another driver to make some kind of roll. It can be a save, a driving roll, whatever. It has to be narratively consistent (no whales dropping from the sky) but it can be a result of anything that makes sense within the narrative framework of a post-apocalyptic world (including mutant creatures erupting from the ground, pits opening under the combatants, and the sudden appearance of dangerous road debris.)
The player rolls a number of d6’s equal to the sum of his driving skill and the Speed score of his vehicle. (Speed here refers to an abstract number from one (a tractor) to three (a motorcycle) that abstracts the acceleration and handling of the vehicle. This idea comes from Stars Without Number and Other Dust, in which vehicles can be improved by adding to their speed score.) In games where skills are usually between zero and four, this means that better drivers in better cars are luckier than rabble in rat rods. So be it.
If our hero, (let’s call him Max), is an exceptional driver (+4) and is driving a fast, black car with a speed of four, he will roll eight d6’s at the beginning of each turn. Each instance of doubles will enable Max to narrate a check or save by one of his opponents. Failure on these checks or saves usually means death or at least a crash that takes a vehicle out of the scene. These crashes can provide the means for another check or save, if the player has enough adrenaline double to accommodate them. The purpose of these checks and saves is to create a sense that no one is in control of the combat once it starts; NPC’s also get adrenaline dice and can provoke other combatants to make checks and saves as well.
A faction of NPC’s would have only one adrenaline pool. If a boss with a +2 to driving in a ground car +2 had four henchmen +1 on motorcycles +3, he would roll eight adrenaline dice. Each NPC should not have his own adrenaline pool; NPC’s of a type can contribute their common scores for driving and Speed.
Since RPG’s often have player characters as passengers, they passengers also get roll Adrenaline dice (which are a narrative device and not a measure of anything.) Passengers can use their driving, Luck, Shooting, or whatever else would contribute to the likelihood of violence in a vehicular battle to total their adrenaline dice. A passenger with a Luck save of +3 would roll three adrenaline dice.
These rules should be adaptable enough to use with many kinds of games; the Speed scores of vehicles can be assigned on the spot. I welcome feedback on these rules, and I’d love to hear from anyone who uses them in a game. Have a lovely day!