Final answer:
The number of vehicles you should allow to accumulate behind you before pulling over varies by location, but commonly, after being followed by two or more vehicles, it's advisable to pull over and let them pass when safe. Always check local traffic laws for the specific requirements.
Step-by-step explanation:
If you're driving a slow moving vehicle and see two or more vehicles following you, many regions require that you must pull over and allow them to pass when it is safe to do so. The exact number can vary, however, depending on specific local traffic laws and rules. As such, it is recommended that drivers familiarize themselves with the traffic regulations applicable to their location.
For example, some jurisdictions state that if you're driving slower than the normal speed of traffic at the time and place and under the conditions then existing, and if you're being followed by a queue of two or more vehicles, a driver must usually endeavor to ease the flow by pulling over when safe and practicable to let the vehicles pass. This prevents traffic build-up and promotes overall safety and efficiency on the roads.