The Formula For Perfect Parallel Parking You finally find a spot along the curb, between two hulking SUVs, and it looks pretty tight. Do you go for it or move on? Not to worry; geometry can save you.
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The Formula For Perfect Parallel Parking

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The Formula For Perfect Parallel Parking

The Formula For Perfect Parallel Parking

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  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
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How many of you absolutely dread parallel parking? A lot I bet. Well, a British mathematician may have an answer, geometry. Simon Blackburn, a professor at the University of London says you can run a simple calculation and, voila, youre in. Here to discuss the theory is Keith Devlin, WEEKEND EDITIONs math guy. Welcome back, Keith.

Dr. KEITH DEVLIN (Co-Founder and Director, H-STAR Institute, Stanford University): Hi, Audie, nice to be back again.

CORNISH: So, whats the basic idea behind Professor Blackburns research?

Dr. DEVLIN: It's actually a very clever use of simple mathematics. In fact, the most complicated bit of mathematics it uses is our good old friend Pythagoras theorem.

CORNISH: That's a2 + b2 = c2, right?

Dr. DEVLIN: Absolutely. And thats really all you need, you just need to use that in a clever way. You put in a few figures about the size of your vehicle and the space that youre trying to get into. And the formula tells you exactly how much extra space you need, beyond the length of your vehicle, in order to park it in a simple, reverse-in, straighten-the-wheels, and switch-the-engine-off move.

CORNISH: So, give us a sense of how detailed the math is. What are the numbers you need to calculate using this system, and is it really practical?

Prof. DEVLIN: Simon Blackburn's formula and these four pieces of information. First of all, you have to tell it the radius of your cars turning cycle. That means if you give it a full lock to the left or right, it will turn in the circle. The radius of that thing is called the turning radius.

It needs the wheel base of your car which is the distance between the center of the front wheel and the rear wheel on either side. It needs the distance from your front wheel from the center of the front wheel to the front bumper. And the one extra piece of information it needs, you know, you pull up next to a car you need the width of that car.

CORNISH: Now I went out and did my parking job, which does involve a certain kind of estimation, where I pull up to the first car. And as Im reversing, I wait until the wheel sort of match up, then I jackknife into the space.

(Soundbite of laughter)

CORNISH: And so Ive got my own sort of estimation and is a lot of this just based on your ability to do that kind of guess work?

Prof. DEVLIN: Yeah, and, you know, there are lots of examples when people look at saw the baseball field and various athletes, and people have put in wonderful shots on the basketball courts. Whats going on is that mathematics gives you a way of understanding in detail what people have learned to do simply by practice and expertise.

In fact, when we practice something, be it on the athletic field or in an automobile, we are becoming very good mathematicians at doing a particular kind of operation. But usually, we don't call it mathematics and we certainly don't give people a pass on the math test because they can park their car.

CORNISH: WEEKEND EDITIONs math guy, Keith Devlin, also a professor at Stanford University. Keith, thanks so much.

Prof. DEVLIN: Okay, my pleasure, Audie.

CORNISH: As a native Bostonian I consider myself a wicked good parker, so I decided to put my skills to the test, right outside NPR headquarters.

(Soundbite of car)

CORNISH: We pull up to the first car, length to length, nose to nose. You essentially want to measure - youre kind of like measuring the space by measuring this car in front of you. And the measure of a perfect parking job according to this mathematician is no back and forth, so thats we are aiming for here. So, now that my front wheel and the back wheel are lined up, Im backing in. Release, release, release of the wheel. Were in the space. Were looking good. Im stopping.

(Soundbite of break)

CORNISH: How far are we from the curb? Okay...

(Soundbite of laughter)

CORNISH: Oh, look at that, thats like nine inches, thats genius.

(Soundbite of music)

CORNISH: Youre listening to WEEKEND EDITION from NPR News.

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