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What is the shortest space a parked car can get out of? Or a parking car can get into?

Hillary Shaw
Newport, Shropshire, UK

Since cars are essentially rectangular, the very shortest space a car can theoretically enter or exit, by 笔测迟丑补驳辞谤补蝉鈥檚 theorem, is the diagonal from one front corner to the back corner on the opposite side, so 4.47 metres for an average car of 2 脳 4 metres.

However, at this diagonal point, the (for example) left rear corner of the car is touching the kerb, the right rear corner is touching the car behind, the front left corner is touching the car in front and you have no space to manoeuvre to get fully in. Geometrically, if the car could rotate, you would need the same 0.47 metres at the front to swing the car fully in, total space required 4.94 metres. However, car wheels on an axle cannot physically turn by 90 degrees, so even this 4.94-metre space would require an approaching-infinite-point turn to enter. You can spend approaching eternity to get in that space, or look for another space of maybe 5.5 metres.

It is also possible to shift an adjacent car either by shunting or simply by nudging up and using your engine to overcome the other car鈥檚 brakes. But I don鈥檛 think this parking method is approved in the UK Highway Code.

Chris Maynard
London, UK

Assertion: the smallest space a parking car can get into is 8 centimetres less than its length. Evidence: my wife and I were in a bar in Paris, sat facing the street. A woman pulled up to a space shorter than her Renault and backed into it. As her bumper touched the car behind, she accelerated until the parked car鈥檚 bumper crumpled 鈥� as did hers. She then drove forward and did the same again, got out, locked the car doors and disappeared into an apartment block. Finishing our negronis, we walked along counting crumpled bumpers. None was untouched.

Jeff Stanton
Sydney, Australia

To park a car requires a series of 鈥渟鈥�-shaped mirror image movements of the front wheels while moving backwards and forwards to manoeuvre the rear wheels near the kerb. With patience, this can probably be done with 50 millimetres or less of spare space. But in practice, things like the road鈥檚 camber, the steepness of a hill, manual transmission, no power steering, an unseen towing ball on the car in front and the patience of the traffic held up behind the parking car will add degrees of difficulty to the task.

On the other hand, performing the manoeuvre in front of a shop with a plate glass window will let you watch the reflection and make the best use of the space.

In practical terms, a space about 300 mm longer than the diagonal of the car seems about the limit.

Eric Kvaalen
Les Essarts-le-Roi, France

Mathematically speaking, there is no shortest space. As long as the space is longer than the car, it is theoretically possible to get in or out of it by doing a large number of back-and-forth movements. Provided the difference between the length of the space and the length of the car is positive, it is possible. If the difference is zero, it is impossible. So, the question is like asking what the smallest positive number is, and the answer is that there is no smallest positive number.

Tony Durham
Brighton, UK

The shortest space you could drive straight into or out of would have to be at least the diagonal dimension of the car. How closely this limit can be approached may depend on how tightly the vehicle can steer.

To escape from shorter spaces, you have to drive forwards and backwards repeatedly, while applying out-of-phase wiggles to the steering. Those lucky enough to understand alternating current circuit theory may see analogies here. Unparking is a lot like getting electrons to do useful work while they shuttle back and forth within the same piece of wire.

In shorter spaces, the required number of iterations tends to infinity and the margin of error tends to zero. But, in theory, you can escape from any space longer than the vehicle.

By performing the same actions backwards, in principle, you could park in a space barely longer than your car. But most drivers try to avoid having to do that. You can鈥檛 choose the new configuration of cars in the place you parked 4 hours ago, but you can choose where you will park right now. My rule of thumb is to find a space at least 50 per cent longer than the car.

David Pitcher
Auckland, New Zealand

I have always found that if I want to parallel park in one move, the length of the vehicle plus its width is the smallest space I can get in. If I am boxed in, having half the width free is a minimum, but it takes three or four tries (and a reversing camera) to extricate myself without hitting the vehicles in front or behind me.

Patrick Forsyth
Maldon, Essex, UK

Many years ago, when I was at school, a favourite trick was to get a gang of pupils together and lift a master鈥檚 Mini, wedging it between two trees. You only needed a couple of centimetres each end to get it in, but it could only be got out by more lifting. I think cars are heavier these days.

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