The following was posted to the labmembers mailgroup, a discussion forum for League of American Bicyclists members, by John Forester, the author of Effective Cycling and many other works on cycling transportation engineering:
A cyclist who is competent in traffic is one who obeys the five principles of traffic operation, who understands traffic flow so that he or she can detect when some driver is not acting normally, and who has several methods for avoiding the most frequent problems.
The five principles:
1. Drive on the right side of the roadway, never on the left and never on the sidewalk.
2. When you reach a more important or larger road than the one you are on, yield to crossing traffic. Here, yielding means looking to each side and waiting until no traffic is coming.
3. When you intend to change lanes or to move laterally on the roadway, yield to traffic in the new lane or line of travel. Here, yielding means looking forward and backward until you see that no traffic is coming.
4. When approaching an intersection, position yourself with respect to your destination direction -- on the right near the curb if you want to turn right, on the left near the centerline if you want to turn left, and between those positions if you want to go straight.
5. Between intersections, position yourself according to your speed relative to other traffic; slower traffic is nearer the curb and faster traffic is nearer the centerline.
Examples of ways to detect when another driver is failing to operate properly:
The driver who overtakes you as you approach an intersection may be just overtaking you, or he may be intending to turn right. The driver who intends to turn right may well slow down, adopt a more rightward position, and, if he does start to turn, you can see the movement start. Watch actual speed and listen to engine noise for signs of slowing down. Watch the position to see if it looks further right than for going straight. Any rightward steering movement of the right front wheel or any lateral movement of the front of the car is a definite clue. React as early as you have any suspicion and take the appropriate avoidance maneuver.
The driver from the other direction and in the center lane who slows upon approaching an intersection that is close in front of you probably intends to turn left. You have the right of way, so he should wait for you. If the car does not slow sufficiently to indicate coming to a stop, or if it swings to its left more than just to the centerline, watch out. If it crosses the centerline, unless it is going very slowly with obvious intent to wait until you have crossed the intersection, then assume that it will continue its turn and take the appropriate avoidance maneuver.
Three methods of avoiding the common problems:
1. For both the motorist right turn and the motorist left turn, it is frequently necessary to make an instant right turn, moving between the threatening car and the curb in the new direction.
2. If you have sufficient distance, it is better to stop than to turn, so you need to know how to make a maximum deceleration stop. Even if the stop won't stop you in time, it often reduces your speed enough so that once you get to a sufficiently low speed you can release the brakes and turn sharply away from the danger.
3. Always beware of parked cars with people in them, either as seen through the windows or by evidence of recent movement, backup lights, or just parked in a high-turnover location (short parking times). Leave a door's width clearance if at all possible.
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