How to play Traffic Jam
A 6 × 6 car park, packed. Cars take two bays and vans three, and each one can only roll forwards or backwards along its own lane. Your red car is on the third row, and the exit is a gap in the wall at the right-hand end of that row. Slide the others out of the way and drive it out.
It is the sliding-block puzzle best known as Rush Hour. There are three difficulties and 160 car parks, from six moves to more than forty, and every one comes with its par: the fewest moves out, worked out by a solver.
Rules
- Drag a car or van along its lane. Nothing turns or changes lanes, and nothing passes through another vehicle or the wall.
- A move is one slide of one vehicle, however far it goes. Nudging the same vehicle several times in a row still counts as one move, and nudging it back to where it started takes the move back.
- The puzzle is solved when the red car reaches the exit: the barrier lifts and it drives off.
- Par is the fewest moves that get the red car out, found by trying every position the car park can reach. Your time goes on the boards; your moves and the par are shown beside it.
- The clock starts with your first move and pauses while the tab is hidden. Each difficulty keeps its own car park, so you can switch and come back.
Controls
- Drag (mouse or finger)
- Slide a car or van along its lane
- Tab / Shift+Tab
- Select the next or previous vehicle
- Arrows along its lane
- Slide the selected vehicle one bay
- Arrows across its lane
- Select the nearest vehicle that way
- Z / Ctrl+Z
- Undo the last move
- R
- Back to the start
- P
- Pause
Tips
- Work backwards from the exit. Find what blocks the red car, then what blocks that, and so on: the chain tells you which vehicle has to move first.
- A van standing upright across the exit row can only clear it by going all the way down, so the bottom three bays of its column have to be empty first.
- Don’t tidy up. Moving a car that isn’t in the chain costs a move and often closes a lane you need later.
- In the hard car parks the red car often has to back away from the exit first. If you are stuck, try the move that looks like the wrong direction.
Traffic Jam strategy
Read the chain back from the exit
Before you move anything, list what stands between the red car and the gap, then for each of those what stops it from leaving row 3, and so on. The first vehicle to move is usually at the far end of that chain, often nowhere near the red car. A vehicle blocks the exit row for good only if it can’t clear it in either direction.
Vans across the exit row go down
A van standing upright covers three of the six rows. Rows 1 to 3 include the exit row, so the only way out of it is all the way down to rows 4 to 6. Whatever sits in the bottom three bays of its column has to go first. An upright car has two ways out: up to rows 1 and 2, or down below row 3.
Count slides, not bays
Par counts slides, not distance, so a long slide costs no more than a short one. When a vehicle has to move, ask how far it must go to open everything you will need next, and send it all the way at once. Coming back to the same vehicle later costs another move.
When the obvious move fails
In the hard car parks the red car often has to back off from the exit, a van has to go up before it can come down, or a car must make room in a lane that seems unrelated. If the chain from the exit leads nowhere, look for the move that frees two vehicles at once. Undo costs nothing but time.
About Traffic Jam
The puzzle is the work of Nob Yoshigahara, the Japanese puzzle inventor and collector, who came up with it in the 1970s. Binary Arts, now ThinkFun, first sold it in the United States in 1996 as Rush Hour: a 6 × 6 grid with grooves for the cars, an exit and 40 challenge cards. It has sold more than a million copies. On boards of any size, deciding whether a jam can be cleared is PSPACE-complete, as Gary Flake and Eric Baum showed in 2002; on the 6 × 6 board the hardest possible start takes 51 moves.
Every car park here was found by a generator. It parks cars and vans at random, walks every position the lot can reach and keeps the one farthest from any way out, then keeps changing one vehicle at a time while that gets harder. Each car park is filed under Easy (6 to 10 moves), Medium (15 to 24) or Hard (30 or more) by its par, and a separate solver checks every par.
Questions
Is this Rush Hour?
It is the same kind of puzzle: a 6 × 6 lot, cars and trucks that slide only along their lanes, and a red car to get out. Rush Hour is ThinkFun’s boxed version of Nob Yoshigahara’s puzzle. The car parks here are our own, made by a generator, and none is copied from its cards.
How are moves counted?
As in the original: one slide of one vehicle is one move, however many bays it travels. Several nudges of the same vehicle in a row count as one, so dragging and the arrow keys score alike.
Can I beat par?
No, only match it. Par is the exact minimum, found by a solver that tries every position the car park can reach. Getting out at par is the challenge; your time is what goes on the boards.
Is my car park saved if I leave?
Yes, in your browser, one per difficulty. The clock pauses while the tab is hidden, and new car parks favour the ones you haven’t solved yet.
