Keep The Traffic Moving!

The scenario

In this competition, you are the traffic engineer. You control the timings of the lights at the six intersections shown in the picture below. Each road has two lanes, one in each direction. The lanes are each 4 metres wide (so each road is 8 metres wide), and the spacing between the roads is as shown. For convenience we've numbered the lanes from 1 to 10, indicated their directions, and labelled the lights A through F.

You can control these lights yourself through a computer simulation available on our web site.

What You (the Traffic Engineer) Already Know

You have also found that the traffic behaviour (the way a car speeds up or slows down when faced with an obstacle in front, such as a red light or another car) follows a certain mathematical model governed by three numbers c, l, and L (the model is described in the section Details on the Mathematical Model Used).

What You Need to Figure Out

To get the full details on each part you can use the "I", "II", "III" icons at the top and bottom of each page. Here's a brief description of them:

1. How can you use the information you have (the thirteen numbers d[1], . . . , d[10], c, l, and L) to decide whether traffic lights are even feasible, or whether a more drastic solution is required, such as widening the roads or building overpasses?

   In the detailed discussion of this part, we'll give you hints on how basic algebra can be used to come up with a simple set of inequalities that tells whether or not traffic lights would be capable of handling the traffic flow. See if you can figure out this formula. You can test your answer on the computer simulation.

2. What happens when a long light of cars is waiting at a red light, and the line turns green? If you've ever been near the back of such a line, you've probably sat in frustration wishing the cars in front would get a move on! But is it only their slowness in reaction?

   In the detailed discussion of this part, we'll explain how ideas of calculus and " differential equations" can be used to answer the question, and challenge you to find out how long it takes for the line to get moving even if everybody's reaction time is instantaneous and there's no limit on the cars' acceleration power. You may be surprised at the answer, and less inclined to blame the cars in front of you next time you're kept waiting! Note: the mathematics in this part is quite challenging and requires a knowledge of calculus. But you can still watch what happens on the computer simulation even if you can't solve the problem mathematically.

3. Find the best light timings for three specific situations. In the detailed discussion of this part, we give you three different situations (three different sets of numbers for d[1], . . . , d[10], c, l, and L). Your job: time the traffic lights in a way that causes the least amount of delay. This part of the competition is a free-for-all: you can use any combination of mathematical reasoning or pure experimentation. The computer simulation lets you enter timing values, watch what happens, and get a score for how well your timings did. It keeps track of the high score, so see if you can beat it and get a new high score!

Use the links above or below to get more information on each of these three competition questions and on the mathematical model used, or to access the computer simulation.

Good luck!