When are bicyclists allowed to ride two abreast in a traffic lane?

Bicyclists are allowed to ride two abreast in a traffic lane when they are in a substandard width lane. A substandard width lane is one that is not wide enough for a motor vehicle to safely pass a bicyclist without encroaching into the adjacent lane. In this situation, riding side by side can help to increase visibility and awareness, both for the cyclists and for motorists, thus promoting safer cycling practices.

In most other scenarios, such as in designated bicycle lanes or when following motorists, cyclists are typically encouraged to ride single file to facilitate smoother traffic flow and safer conditions on the roadway. Riding two abreast in those instances can obstruct traffic and create safety issues. Riding two abreast on a one-way street is not inherently a violation, but it does not specifically relate to the conditions of substandard width lanes and might not always be a safe practice depending on traffic density and road conditions.