Gridlock
Also known as Traffic Jam, Car Park Puzzle, Parking Puzzle and Sliding Block Puzzle
A jam of cars and lorries, and yours has to get off the right-hand edge. Every vehicle slides only along its own length, so clearing a path means working out what has to move before what. Every board shows the fewest moves it can be solved in, measured rather than guessed.
How it works
- Drive the marked car off the right-hand edge.
- Drag a vehicle to slide it. Each one only moves along its own length — cars never turn.
- Vehicles cannot pass through each other, and only your car may leave the grid.
- Undo takes a slide back, and Reset returns the jam to how it was dealt.
- Pip's best is the fewest moves this exact board can be solved in — measured, not estimated.
- One free hint plays a move on the shortest route from your current position.
- Match Pip's best without hints for a Perfect result. Perfect it lets you replay the same jam to improve your route.
- Every jam has a solution.
Good if you want…
- Finding the fewest moves possible
- No reading, no arithmetic
- Working out the order things have to happen in
How to solve Gridlock
Work backwards from the exit
Start with what is directly between your car and the right-hand edge. For each vehicle in the way, ask where it would have to go to clear the path. Then ask what is stopping it from going there. A solution is a chain of these answers, and it is much easier to build from the exit backwards than from the starting jam forwards.
Up or down?
A lorry blocking your row can often move either up or down to get out of the way, and one of those directions is usually far cheaper than the other. Before committing, look at what each direction needs to clear. The wrong choice is where most extra moves come from.
Count moves, not squares
Sliding a vehicle any distance along its lane counts as one move. So when you move something, move it as far as it will need to go, not one square at a time. That is the difference between matching Pip's best and missing it.
Use Reset without shame
Once you have worked out the order things must happen in, it is often quicker to reset the jam and play the solution cleanly than to undo your way back. Pip's best is the true fewest for that exact board, measured by a solver, so beating it is impossible — matching it is the goal.
Common mistakes
- Moving vehicles that are not in the chain. Every move should be clearing space for something that is.
- Moving a vehicle one square at a time. Each slide is a move, whatever its length.
Where Gridlock comes from
Sliding-block traffic puzzles grew out of older sliding-block puzzles in the twentieth century and became popular as boxed games with plastic cars and lorries. Their appeal is that the rules take one sentence and the solutions can run to dozens of moves.
Gridlock questions
What is Pip's best?
The fewest moves that exact board can be solved in, measured rather than estimated, and named for Pip, the Winters Puzzles penguin. Every jam has a solution.
Can vehicles turn?
No. Each vehicle only slides back and forth along its own length.
Gridlock in Winters Puzzles
Gridlock is one of 40 puzzles in Winters Puzzles, so it sits alongside Tessera, Ripple, Flow and everything else in the app rather than being a download of its own. It counts towards your stats and streak like any other puzzle. It is not one of the puzzle types included in Pip’s dailies.
Play Gridlock.
Free on iPhone and iPad, with 39 other puzzles alongside it. Or play it in your browser — no download, nothing to sign up for.
