When traversing an intersection, you should be in the correct lane as for any vehicle. For example, if you're going straight through and the right lane has turned into a right-turn only lane, you need to shift to a middle lane. If you're turning left, and there's a left-turn lane, you need to get into it.
Maintaining a straight line while looking behind
To shift lanes or turn safely, you need to check behind and make sure it's safe to turn, and you need to be able to do so without swerving. This is not difficult, but it may take some practice.
Find a placeâno traffic and plenty of roomâwhere you can ride safely while looking behind you for some time. The key is to keep your shoulders and body square to the front and turn only your head and neck. Riders who are leaning forward will sometimes look under an arm rather than over the shoulder. Practice both sides. Find or make some kind of line on the ground so that you can detect if you are swerving.
How to shift lanes
Shifting lanes on a bicycle is no different than shifting lanes in a motor vehicle. You must look back and you must signal. You must not change lanes unless there is an opening for you to do so. If there's a vehicle approaching, wait until you are certain the driver is yielding to you (they may not). If crossing multiple lanes, change one lane at a time. Sometimes, hand signals will be difficult because of high speed or riding position; in such cases you can often make your intention clear by looking behind you.
Lane position during turns
Proper lane position during turns is important to avoid being squeezed by vehicles that are turning at the same time.
When making a right turn, take the middle of the lane to prevent being squeezed to the right and possibly into the curb or street corner. Vehicles making the same turn in the same lane should be in front of or behind you.
When making a left turn, take the center-right of the lane to prevent being squeezed to the left into a center or wrong-way lane. If you are turning onto a high-speed road, it's okay for vehicles to turn with you to your left, but not to your right.
Sometimes you miss your turn
Sometimes you can't make your lane shift in time. Sometimes you don't know the route well enough to anticipate your lane shift in time. Don't force it. If you miss your turn, find a safe, legal way to turn around and come back the other way. Or, simply (and safely) stop at the other side of the intersection and walk your bike through the turn as a pedestrian.