Final answer:
When passing another vehicle on a freeway with a posted speed limit of 55 mph, you are not legally allowed to exceed the speed limit. You must pass safely without exceeding the legal threshold. Traffic conditions and common practices do not override the legally posted speed limits.
Step-by-step explanation:
The speed limit is a legal threshold set for road safety and is the maximum speed at which a vehicle can lawfully travel on a particular road. When lawfully passing another vehicle on a freeway where the posted speed limit is 55 miles per hour, most state laws do not authorize exceeding the speed limit. Instead, drivers should pass safely within the designated speed limit. A common misconception is that there is a grace amount by which drivers can exceed the speed limit to pass, but this is generally not the case. Drivers may perceive a de facto speed limit, which refers to the actual speed driven by most motorists, or the threshold above the posted limit before law enforcement is likely to issue a ticket. However, the de jure, or legally enforced limit, is the speed drivers must adhere to.
One should not confuse permissible behaviors while merging onto a freeway or during other driving adjustments with passing on the freeway. When merging onto a freeway, drivers typically accelerate to match the speed of traffic for safety reasons. However, this should not be misinterpreted as license to exceed speed limits during regular travel and passing maneuvers.