How is riding side by side in a lane dangerous?

When there's a dedicated bike lane or a wide shoulder, riding side by side impedes car traffic unnecessarily. In this situation, when cyclists are riding single file, vehicles can pass without needing to enter the opposing lane. Riding two or three abreast, vehicles cannot pass without needing to enter the opposing lane.

In the absence of a bike lane or wide shoulder, I don't feel that it matters much as it's just an unsafe situation regardless - there's an argument that a large group in a pack is shorter and therefore safer and easier to pass, an argument that having to swing "wide" into the opposing lane is more dangerous, an argument that cyclists in this situation simply should not be passed (in which case IMO they should pull out at the next opportunity, just as a slow motor vehicle would be required to do in many states), and an argument that the situation shouldn't exist to start with.

Is it illegal for cyclists to take the lane where you live? If you're doing that I don't understand why it makes a difference if it's 1 person taking the lane or 2 abreast. Either way the lane is taken. Trying to leave a fraction of a lane open to drivers just seems like a good way to get sideswiped

I'm not sure what the laws are in the rest of the country / world, but at least in California you cannot simply take the full lane as a cyclist at any time. There are specific situations where you can -- such as to avoid a hazard in the bike lane or when turning at an intersection -- but you can't ride in the middle of the lane always.

https://leginfo.legislature.ca.gov/faces/codes_displaySectio.... https://leginfo.legislature.ca.gov/faces/codes_displaySectio....

If I'm parsing that correctly, those limitations on taking the lane are only for roads that have real bicycle lanes. For the vast majority of roads, it's legal to take the full lane.

While not in the same section as posted above, the ~same limitations apply.

Any person operating a bicycle upon a roadway at a speed less than the normal speed of traffic moving in the same direction at that time shall ride as close as practicable to the right-hand curb or edge of the roadway except under any of the following situations:

(1) When overtaking and passing another bicycle or vehicle proceeding in the same direction.

(2) When preparing for a left turn at an intersection or into a private road or driveway.

(3) When reasonably necessary to avoid conditions (including, but not limited to, fixed or moving objects, vehicles, bicycles, pedestrians, animals, surface hazards, or substandard width lanes) that make it unsafe to continue along the right-hand curb or edge, subject to the provisions of Section 21656. For purposes of this section, a “substandard width lane” is a lane that is too narrow for a bicycle and a vehicle to travel safely side by side within the lane.

(4) When approaching a place where a right turn is authorized.

(b) Any person operating a bicycle upon a roadway of a highway, which highway carries traffic in one direction only and has two or more marked traffic lanes, may ride as near the left-hand curb or edge of that roadway as practicable.

https://leginfo.legislature.ca.gov/faces/codes_displaySectio....