This information is reprinted with permision from Michael Bluejay and his site Bike Safe
It's often safer to take the whole lane, or at least ride a little bit to the left, rather than hug the right curb. Here's why:
Cars at intersections ahead of you can see you better if you're squarely in the road rather than on the extreme edge where you're easily overlooked.
Taking the lane prevents cars from passing you too closely on narrow roadways.
Riding a bit to the left prevents you from being a victim of the door prize.
You might worry about slowing down the traffic behind you if you take the lane. But if you're on the kind of street where you've got cars blocked up behind you or constantly changing lanes to get around you, you're probably on the wrong street and should find a quieter neighborhood street.
Taking the lane works especially well in most traffic circles. The traffic generally moves slower so it's easy to keep up, riding in the lane makes you more visible to motorists, and taking the lane prevents motorists from right hooking you as they exit the circle.
It's perfectly legal for you to take the lane when appropriate. State Law says you have to ride as far to the right as is "practicable". Here are some things that make it impracticable to ride to the extreme right:
You're in a heavy traffic area with lots of side streets, parking lots, or driveways ahead and to your right. Cars turning left won't see you because they're looking for traffic in the middle of the road, not on the extreme edge of the road. Move left.
Cars are passing you too closely. If the lane is too narrow for cars to pass you safely, then move left and take the whole lane. Getting buzzed by cars is dangerous.
Cars are parked on the right-hand side of the road. If you ride too close to these you're gonna get doored when someone gets out of their car. Move left.
There are risks to both riding to the extreme right as well as taking the lane. Whether you ride to the right or take the lane depends on the conditions of the roadway you're on. On wide roadways with few intersections/driveways, right further right. On narrow roads with lots of intersections, ride farther to the left. It's not always better to take the lane or to hug the curb; it depends on the roadway you're on.