How Cloverleaf's traffic works

01Every truck is real

You don't buy trucks in Cloverleaf, and you never own one. You draw a supply line from one building to another, and the line sends out a truck for each load, the way a conveyor carries items. That truck then has to really drive there, wait its turn at the dock, and drive home empty. It only leaves the road when it gets home.

Nothing is faked to keep things moving. Trucks never despawn, never teleport, and never squeeze through each other. If the road can't carry the trips your factories need, the trucks queue, the loads wait, and your factories slow down. That's the game: traffic is your throughput.

Try it

A sawmill and its supply line

Each load gets its own truck. Raise the demand until the depot's one dock can't keep up and watch the queue grow back up the road. Break down a truck to close the lane, then tow it.

Demand

Illustration. Yellow trucks are loaded, outlined ones are on their way home, and a red tail means stopped.

Trucks are paid for per trip, so a line costs only what it really uses. As your city earns more from exports, bigger truck types open up for its lines. A short jam won't take them away again: when you clear it, the city climbs back to where it was by itself.

02The whole city, alive

Climb a tower or take the helicopter up, and the whole city should still be moving: every street with its real traffic, out to the horizon. Simulating tens of thousands of trucks and cars in full detail, all at once, isn't possible on a home PC. So Cloverleaf splits the job in two.

The count is always exact. The simulation tracks every vehicle on every road in the city, all the time, wherever you're looking. A jam on the far side of town is a real jam, with the same trucks in it.
The drawing gets simpler with distance. Near you, each car drives itself: it brakes, changes lanes and pulls aside for an ambulance. Farther away the same cars are drawn as simpler models, then as headlight pairs, and at the horizon as a glow on the road, brighter where there are more cars.

Only the drawing is simplified. The models, colors and exact spots of far-off cars are made up, but how many there are never is. A jammed road looks jammed from anywhere, and an empty road is dark.

Look closer

One city, drawn five ways at once

A street grid running away to the horizon. Turn each kind of drawing off and on, or slide over to see which one each car falls in. Point at the picture (or tap it) to see what's drawn at that distance.

As drawn Which kind

drives itself
full car
stand-in
speck
glow on the road

Every car in the scene is counted the same way, whichever way it's drawn. Turn off the far drawings and the horizon goes quiet; the cars are all still there. The dashed lines in the "which kind" view mark where the drawing changes. Illustration

From above

The bubble follows your eyes

Seen from straight above: the yellow bubble is where cars drive themselves. It sits around you and leans toward where you're looking, so the cars you can see up close are always the detailed ones. Turn around and it swings with you. Past it, the same cars are drawn more simply in rings.

Bubble size

Illustration. The counts change as cars move between rings, but the total never does.

03Jams are puzzles

Because nothing despawns, a jam is real: a broken-down truck closes a lane, the queue backs up, and if it reaches the junction behind it, cars on the cross street can't get through either. Your factories slow down and your income dips. But a jam is never a ruin. Nothing is damaged or lost, and once you clear it, the city drains back to full speed by itself.

Scrub through it

Ten minutes on Main Street

Seen from above: a delivery truck breaks down in the eastbound lane. Drag the slider to watch the queue grow, spill back across the junction, then drain away after the tow.

Time

One closed lane can stop a whole junction, and clearing it is all it takes to recover. Every car here is moved by a small traffic model, so the queue grows and drains the way a real one does. Illustration

Finding the jam

A jam has to be easy to find, or it's just frustrating. The planner tablet leads you from the symptom to the place in a click or two: a money shortfall or a starved building shows which supply line is short, and the traffic view shows that line's route glowing where its trucks are queuing, drawn thick and with chevrons, so it reads without color too.

The tablet tells you what is wrong and where, never the fix. It names the jammed junction and the starved line, but it won't tell you which junction to rebuild or which lane to repaint. Working that out is the fun part.

A new jam every tier, and the tools to answer it

Traffic tuning is about half the game, so it can't be the same puzzle at a bigger size. Each tier's economy creates a new kind of jam, and the same tier hands you a tool for it. Slide through the tiers to see what turns up.

Tier

04Walkers count too

People on foot are real traffic as well: commuters walking to work, riders walking to the bus stop, shoppers and visitors. Busy sidewalks slow everyone down, and crossings take green time from cars, honestly, by how many people are really waiting. A light only gives a walk signal when someone is waiting, and holds it longer when more people are. At crossings without lights, turning cars wait for walkers.

Walkers use the same trick as cars. Near you, everyone is a person walking on their own. Far away, a group heading the same way is kept as one bunch with a headcount, so the count stays exact but the work stays small.

Try it

A crossing with a walk signal

Add more people and watch the walk step come sooner and last longer, while the cars wait. Switch to the far view to see the same people kept as bunches with a count.

People on foot

Illustration.

05A city that stays smooth

Big city builders tend to bog down as the city grows, because they redo work for everything that exists, every tick. Cloverleaf's rule is the opposite: the work grows with what changes, not with how big the city is. A settled factory or a quiet suburb costs almost nothing. And if a slow PC ever can't keep up, the game slows its clock and tells you, instead of cutting corners: the city plays out the same on every PC.

Two things players do a lot used to cause a stutter in our tests, and now don't: making a lot of edits at once, and jams. A jam now costs about the same to simulate as the same traffic flowing freely.

See the difference

A burst of edits, before and now

Each bar is the simulation's work in one moment of play. Drop a big blueprint, or cause a jam, and see what happens to the line.

Illustration of the effect, not a measurement. The measured numbers are in the next section.

06Measured so far

We test with bench cities: a reference city the size of a finished game, at 20,000 vehicles, a stress city four times bigger, at 80,000, and a stretch city eight times bigger, at 160,000. These numbers come from the simulation alone, run without graphics on our development PC. They are not frame rates in the game, which doesn't draw these cities yet.

160,000vehicles in our biggest bench city, all simulated at once

≈ samea jam costs within 4% of the same traffic flowing, at every city size

> 100×faster to take in a big burst of edits, in the stress city

≈ 60%less time to update the traffic far from you, in both the reference and stress cities

Measured · lower is better

Updating far-off traffic

The traffic far from you now updates in well under half the time it took before, in both cities. Milliseconds per update.

Measured · lower is better

The first moment of a big edit

A big burst of edits in the stress city no longer lands all at once: the first update after it is over 100 times faster. Milliseconds, on a log scale.

07What's next

Working now

The traffic model for the whole city, with real queues and no despawning
Route choice: each truck takes its own quickest way
Cheap edits and cheap jams, measured in the bench cities

Being built

Roads, supply lines and the first jam you can play
The game drawing its first real traffic

Later

Cars that drive themselves around you, in the bubble
The far-off drawing, out to the horizon
Walkers, commuters and the living city

We'll update this page as each piece lands, and we'll keep saying which numbers are measured and which pictures are illustrations.