Start with the trunk

Four ideas hold this book up.

Remember these and the rest is detail.

1. A traffic signal is a computer standing on a street corner.

2. Whoever can reach the controller can run the intersection.

3. Flashing red is safe. The street still has to move.

4. Close the path. Keep the street moving.

Chapters 1 and 2 prove the first idea. Chapters 3 and 4 prove the second. Chapters 5 to 9 show the third and fourth at work.