You can always cross a single broken white or yellow line except under which condition?

Crossing a single broken white or yellow line is permissible under most circumstances, as these lines indicate areas where lane changes are allowed. However, one critical condition that prohibits crossing these lines is when doing so interferes with the flow of traffic. This is essential for maintaining road safety and ensuring smooth transportation. If you attempt to change lanes or cross the line and end up causing disruption or risk an accident, it creates a dangerous situation for all road users. Hence, it’s important to only cross these lines when it's safe to do so without impacting other vehicles.

In contrast, being in a hurry, having no oncoming traffic, or needing to make a turn do not inherently justify disregarding safe driving practices when crossing these lines. Always prioritize safety and traffic regulations over convenience or urgency.