How to play Gridlock

Gridlock looks like a traffic puzzle and is really a reading puzzle. One rule governs everything, and one guarantee changes how you should play it.

The rule

Each vehicle points at exactly one of the four walls. Between it and that wall lies a lane of squares. A vehicle can leave when two conditions hold together:

1. Every square in that lane is empty. 2. The wall has a **gap** where the vehicle would pass through.

The second condition is the one newcomers miss. The perimeter is mostly solid; the gaps are the breaks in it, each marked with hazard dashes just outside. A car with a completely clear lane that points at solid concrete is going nowhere, and it will brake and honk if you ask it to.

Cars occupy two squares, trucks three. A vehicle is either parked where it started or gone — nothing shuffles forward, nothing rotates.

The guarantee

**You cannot get stuck.** Not by choosing badly, not by clearing in a foolish order.

Driving a vehicle out only ever empties squares — it can never fill one. So a lane that was clear before your move is still clear after it, and a lot that could be emptied before your move can still be emptied after it. Every legal tap is safe, permanently.

The lots are built to match. Each is generated backwards: a vehicle is only ever parked on a spot whose lane and gap were already open at that moment. Play the parking order in reverse and you have a complete solution — so the lot you are handed was solved before it was drawn. The same construction is why you will never find a car nose-up against a solid wall with no way out: one could never have been parked there.

The practical upshot: if you can see a car that is free, sending it is never a mistake. There is no need to plan a sequence, hold a line in your head, or undo. There is no lose condition because there mathematically cannot be one.

So what is actually hard

If every legal move is safe, the skill is reading rather than ordering. Two things genuinely take effort:

**Checking a lane and its gap together.** A long lane across a busy lot is easy to misjudge, and it is easier still to trace a clear lane and forget to check whether the wall opens at the end of it.

**Choosing among the many cars that are free.** On a full lot a good fraction of the vehicles can leave at any moment. They are not worth the same.

Convoys, and why they block

Vehicles come in four colours. Send one, then send another of the same colour, and you have a convoy. The second is worth double the first, the third triple, and so on — a run of five is worth fifteen times a single car, not five.

That is where the decision lives. Any free car is safe, but only some keep the run going, and taking a free car of the wrong colour ends a convoy you were building. Sending a car out also frees others behind it — the game rings those the moment it happens — so the strongest play is reading one step ahead for the colour the lot is about to open up.

Convoys are harder to sustain here than in a puzzle with many small pieces: a lot holds roughly fifteen vehicles across four colours, so long runs are genuinely scarce and worth planning around.

Blocked cars

Tapping a boxed-in car costs nothing but your convoy, which resets. The car brakes and the vehicle in its way flares up, which is real information — it names precisely what to clear to open that lane. Using a deliberate blocked tap as a probe is a fair trade, and the game does not punish it further.

The daily lot

Every day brings one seven-by-seven lot, the same for everybody, generated from the date — cars, trucks, colours and wall gaps all included. Clearing it extends your streak. Since a lot cannot be failed, the daily is a run for time and score rather than a survival test, and the share text carries your time, longest convoy and score without giving away the lot itself.