h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Although the concept of a roundabout is fiendishly clever, the people who use them often are not. The rules are simple, yet people seem to be confused by them. The two main areas of confusion are Right of Way and Indication.

Right of Way

Disregarding those roundabouts with traffic lights on them, the rule here is "always give way to traffic approaching from your right." Devilishly simple. The problem occurs when people arrive at the roundabout from each of the roads it joins all at once. Since everyone is waiting for the person to their right, a stalemate occurs. This is usually solved when the person driving the vehicle with the highest rate of acceleration decides not to wait any longer. The rate of acceleration of a vehicle has been shown to be directly proportional to the number of car horns sounding behind the vehicle in question.

Indication
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Again, disregarding those roundabouts with traffic lights on them, the rules are very simple. The indication process consists of two phases: the approach phase and the exit phase.

The Approach Phase
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Upon approaching a roundabout, one must use one's indicators (those little flashing lights on the corners of the vehicle) to indicate the direction in which one intends to exit the roundabout. As clever as indicators are, they can still only indicate three intentions:

i) I wish to turn left.
ii) I wish to turn right.
iii) I wish to go straight ahead. This is often confused with "I don't know which way I wish to turn", but indecision is outside the scope of this article.

One should indicate "I wish to turn left" if one intends to exit the roundabout at the first available exit. See The Exit Phase for an explanation of why this is the case.

One should indicate "I wish to turn right" if one intends to travel more than halfway around the roundabout.

One should not indicate for any other option.

The Exit Phase
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The rule here is extremely simple: indicate "I wish to turn left" immediately upon passage of the exit prior to the one you wish to take.

Example
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An example often helps to clear up any confusion, so here it is:

I approach a roundabout which has four exits. I wish to turn right at the roundabout, which is the third exit. Upon my approach, I must indicate "I wish to turn right." I pass the first exit, which I would have taken had I wished to turn left. I am still indicating "I wish to turn right." I pass the second exit, which I would have taken had I wished to go straight on. I now indicate "I wish to turn left." I reach the third exit and exit the roundabout.

There are more complicated examples of this, but these are the basic rules that, if followed, will make roundabouts far less confusing.