Introducing the All-New 1019 Toyota Barbarian

I'm playing in a 5e game right now broadly styled after (I am told) JoJo's Bizarre Adventure Part 7: Steel Ball Run. It's a race, run rather loosely (incredibly so by the standards of 5e), and the party has a battlewagon that I take great joy in using as my primary weapon. I'm not quite satisfied with just rolling endless Athletics tests, however, so I decided after seeing the excellent pen-and-paper game Racetrack that I could write up some proper system-agnostic (though GLOG-intended) Vehicle rules. These aren't as rules-light as some of the stuff I've written, instead intended for a game in which vehicles play center stage.

by 47ness

Vehicles are treated similarly to characters and have the following stats, which can be tested like player character stats in relevant circumstances. All stats are determined by the vehicle's Chassis, which gives typical ranges for the stats.

POWer: top speed, acceleration
HANdling: maneuverability, stopping distance
DURability: withstanding damage, pushing limits
CAPacity: the number of people/stuff it can hold comfortably (1 CAP ~ 10 inventory slots, or one person)
FUel: the maximum size of the Fuel die.
Hit Points: as player HP, though measured on a different scale. Damage from person-scale weapons is always minimized unless it's really strong, by the same token damage to people from a vehicle-scale attack is always maximized.

Movement
This system of vehicle movement requires a grid, and broadly follows the rules of Racetrack. Vehicles are marked at intersections of grid lines, not in individual squares, and they move between these points. On its turn, a vehicle can move once. From a standstill it can move to any adjacent point; while in motion it moves almost the same distance and direction it moved the previous turn, but its trajectory can be altered to one of the eight points surrounding the point it would move to if it maintained course and speed. These can be affected further in various ways, detailed below.

Your Speed is the number of grid squares you're traveling in height+width (if you're moving 4 up and 2 across, your speed is 6). Your Power is the upper safe limit on the vehicle's speed. You may make a Power test before moving to increase or decrease your speed by up to the amount of points you succeed by (must follow same ratio as to keep direction of movement constant, rounding down).
If you want to increase speed past Power, make a Durability test. If you fail, take d4 damage from the strain. Whenever your Speed is above your Power, you make Handling tests at disadvantage.
You can make a Handling test to increase the range of squares you can move to by 1, and an additional 1 for each 5 points you succeed by.

Every hour, or whenever you make a move that would deplete Fuel, roll the Fuel die. On a 1, it downgrades. When it's a d4 and downgrades, you're Out Of Gas and need to refuel.

When a vehicle would collide with another vehicle (whether by intentionally ramming or spinning out of control), both take damage equal to the other's hit die, +1 for every 5 POW each vehicle is traveling at (DUR save for half).
Vehicles use DUR to defend against attacks. Any damage that causes a Vehicle to fall to or below 0 HP causes a roll on the Breach table. When a vehicle is reduced to -max HP, it's Slagged; roll to see how.

Breach Table
1. Slowed; lose Speed equal to 2*damage taken, all occupants take d4 damage (DEX save halves)
2. Hull Breach; random occupant takes max damage from breaching effect (CON save halves)
3. Chassis Cracked; -4 DUR, random occupant must save or be thrown from vehicle
4. Popped Tire; -3 HAN, -3 POW
5. Fuel Tank Breached; take FU Die fire damage; everyone inside takes half that much damage (CON save negates)
6. Steering Cut; must pass a HAN save to not move at random; additional Breaches of this result give -3 HAN

Slagged Table
1. Flipped; vehicle is overturned, move vehicle 2 points in random direction and all occupants take vehicle's HD bludgeoning damage (DEX save halves)
2. Shredded; nothing of the outer chassis remains. All occupants take half damage from the attacking weapon (DEX save negates)
3. Burnout; engine block and all interior systems catch fire, all occupants take d8 fire damage (CON save negates)
4. Out of Control; vehicle will continue moving in current direction at increasing speed (making DUR tests to do so each round) until it either crashes or shreds itself from failed DUR tests.

Chassis
Bike: d4 HD, 4d6 drop lowest POW, 4d6 drop lowest HAN, 2d6 DUR, d2 CAP, d6 FU
Car: d6 HD, 3d6 POW, 3d6 HAN, 3d6 DUR, 2d4 CAP, d8 FU
Van: d8 HD, 3d6 POW, 4d6 drop highest HAN, 4d6 drop lowest DUR, 2d6 CAP, d10 FU
Truck: d10 HD, 3d6 POW, 2d6 HAN, 4d6 drop lowest DUR, 3d6 CAP, d10 FU
Tank: d12 HD, 3d6 POW, 1d6 HAN, 4d8 drop lowest DUR, 2d4 CAP, d6 FU
Train: d10 HD, 5d6 POW, 1d6 HAN, 4d6 drop lowest DUR, 6d6 CAP, needs tracks, d12 FU

Light Mech: d6 HD, 3d6/2 POW, 4d6 drop lowest HAN, 3d6 DUR, d2 CAP, d8 FU, Crawler
Heavy Mech: d10 HD, 2d6/2 POW, 3d6 HAN, 4d6 drop lowest DUR, d4 CAP, d8 FU, Crawler
Titanomech: 2d12 HD, 1d6/2 POW, 2d6 HAN, 6d6 DUR, d6 CAP, d4 FU, Crawler

Accessories
Ablative Armor: Reduce damage taken until first Breach by 1 for each attack
All Wheel Drive: Can move twice per turn, at half distance each move
Autobrain: Doesn't need a pilot, will follow simple orders (a short program of directional and acceleration instructions) input through levers in pilot's seat and continue executing them until complete or OVERRIDE switch thrown. 1-in-20 chance to fail to execute any particular order.
Crash Bags: On first Breach, prevent all damage dealt to occupants
Crawler: Legs instead of wheels. Halve POW, but increase range of altering trajectory during move by 1.
Ejection Seat: Can eject pilot in case of Breach or when manually triggered. Launches occupant 2d10*10' away from vehicle. Seat has parachute, deploys on a 5-in-6.
Extra Fuel Tank: Step up maximum FU die size
Extra Seats: Max out CAP
Jump Booster: Deplete FU 1 step to vertically jump (HAN test)*10' up. Test DUR on landing, on fail take HD damage.
Living Quarters: It's got amenities which (CAP/2) people can take proper daily rests in.
Monster Wheels: Advantage on HAN tests to cross rough terrain, ramming also lets you run over the target and make an additional ramming attack
Mounted Weapon: Vehicle-sized weapon; typically some sort of mounted crossbow or cannon, perhaps something more exotic. Deals damage as appropriate human-scale weapon, but sized for vehicles. Always deals max damage to human-scale targets. Takes up 1 CAP.
Muted Engine: Roll over your POW+current Speed to drive stealthily.
Pressurized: Fully sealed environment; unless ruptured, immune to smoke/gas/water/etc
Ramming Prow: Deal ramming damage with advantage, when ramming with prow you take damage at disadvantage
Spiky: Step up damage die for dealing damage ramming or when rammed
Tow Cable: Make an attack against another target to latch onto it, POW test to pull target along with you, only 1 latched target per cable
Trailer: Roll CAP dice and add them to total CAP, anything in those slots are open-air
Treads: Halve POW, but ignore terrain penalties
Turbocharger: Roll to deplete FU to automatically succeed on POW test (if speeding up, roll until you succeed)

Delilah's Different Dealership's Fantastic Selection of Assorted Conveyances
Melf's Magnificent Manacycle (Bike)
POW 18, HAN 13, DUR 5, CAP 1, d6 FU, HP 2
Crash Bags, Ejection Seat

General Magicks 1013 Adventurer (Car)
POW 6, HAN 14, DUR 11, CAP 5, d10 FU, HP 4
Extra Fuel Tank, All Wheel Drive

Kitbashed Battlewagon (Truck)
POW 7, HAN 4, DUR 14, CAP 12, d10 FU, HP 7
Turbocharger, Ramming Prow

Scrapper Unit 01 (Light Mech)
POW 5, HAN 11, DUR 9, CAP 2, d8 FU, HP 5
Crawler, Mounted Cannon, Tow Cable

Some Terrains
Paved Road: No effects
Ice: Handling test to alter trajectory; if you fail alter it at random
Rough Terrain: Make all Power tests with disadvantage
Heavy Precipitation: All tests that require visual acuity are at disadvantage within sight range, and impossible outside it, also may make terrain count as Ice
Thick Brush: All increases in Speed are halved, all decreases are doubled
Back Alleys: Speed-in-100 chance of hitting something important you didn't see whenever you move (examples: cabbage stand, steam valve, flock of dire pigeons, scaffolding, iron fence, pedestrian)
Traffic Jam: Top Speed capped at 3 (if you're lucky)