Final answer:
While the rule can vary, often if five or more vehicles are behind you and you are impeding traffic on a two-lane road, you should pull over when it's safe to do so. Always check local traffic laws for specific regulations.
Step-by-step explanation:
The specific number of vehicles that must be behind you before you are required to pull over on a two-lane road varies by state and local traffic laws. Many states suggest if you are being followed closely by a line of five or more vehicles and you are impeding the flow of traffic, you should find a safe place to pull over and let them pass. However, it is essential to check the specific traffic regulations in your area as this rule can differ. Safety should always be your top priority, so if pulling over can improve traffic flow without putting yourself or others in danger, it is generally considered a courteous and sometimes required action.